dear list, i am a new kayaker (i've started a couple of months ago and gone out about 10---12 times). i have a question about chine and stability. i know chine affects how the boat reads the waves, but how does it affect primary and secondary stability? i'm particularly interested in this from a "how does it feel" rather than a physics standpoint, as i've read about the physics. actually let's make that a "how does it feel to a beginner" standpoint. i'm not afraid to edge, but the boat i'm getting has a very soft chine and i'm curious about other boats with a hard, or hard multi-chine, and what their advantages are. tia for any info. kcd kathleen comalli dillon~friend, mom, wife, musician, violinist, writer, ailurophile extraordinaire ~~~~~~~~~~~~~~ "We can do no great things; we can only do small things with great love."-Mother Teresa~~"I find a lot of people like chubby 67-year-old girls."-Beverly Sills~~"I care not for a man's religion whose dog and cat are not the better for it."-Abraham Lincoln~~"Prepare to be assimila-----OOOOOoooooo, jelly donuts!"-Homer of Borg~~"I am Boris of Borg. Moose and Squirrel are irrelevant."~~ *************************************************************************** PaddleWise Paddling Mailing List - All postings copyright the author and not to be reproduced/forwarded outside PaddleWise without author's permission Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
I guess I'll take an early morning stab since I don't see anyone else answering. A fully rounded hull has no chine, no corners, and being round has no real surprises to feel when hitting the chine or corner. the other extreme would be a flat bottomed boat with a definate corner or chine which when leaned/tipped/edged suddenly gives way. The unsuspecting beginner might lose balance while the experienced person might welcome the additional stability the "side" gives. My boat as an extreme v keel, with chine, and to turn it sharply I have to put it on it's side (which I like). To get the feel, take the boat to a pool and play with the edges. It's better once you can roll, or if you have a friend to give you a bow rescue/hands rescue to that you don't have to spend all the time wet-exiting and re-entering. Do you have a boat in mind? Being a feeling sort, I'll expect some more technical explanations from the rest.. Andree Online Editor Canoe and Kayak Magazine - December Issue Live http://www.canoekayak.com/ Kayak Instruction Excellence http://www.onwatersports.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
I would appreciate any thoughts from those who have paddled Anas Acutas. You can reply directly to me at tfj_at_interaccess.com or generally to the list. 1. How important is a skeg, if one is not paddling in currents, tides, or out of sight of land? My concerns: sand, etc., on beach launches and landings, could eventually foul the mechanism; no matter how good the fittings, there may be some leakage in the long run; and I just don't like the idea of assisted steering. On the other hand, is tracking a little iffy without a skeg? 2. My local dealer said the Anas normally is shipped without footpegs. Did you add footpegs (same concern about compromise of hull integity . . .), or is it just necessary to adapt one's habits slightly to do without them? Tom Joyce *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
>I would appreciate any thoughts from those who have paddled Anas Acutas. You >can reply directly to me at tfj_at_interaccess.com or generally to the list. > >1. How important is a skeg, if one is not paddling in currents, tides, or >out >of sight of land? My concerns: sand, etc., on beach launches and landings, >could >eventually foul the mechanism; no matter how good the fittings, there may be >some >leakage in the long run; and I just don't like the idea of assisted steering. >On >the other hand, is tracking a little iffy without a skeg? > >2. My local dealer said the Anas normally is shipped without footpegs. Did >you >add footpegs (same concern about compromise of hull integity . . .), or is it >just >necessary to adapt one's habits slightly to do without them? > >Tom Joyce > I'm not an Anas Acuta owner, but I've test-paddled one. ;-) Skegs have nothing to do with currents. They are used to counter the tendency of most sea kayaks to turn into the wind, otherwise known as "weather helm." Basically, dropping the skeg keeps the stern from being blown downwind. (You could think of it as a kind of trim tab.) If you ever paddle a boat with weather helm (some have a fairly neutral helm) several miles in a strong quartering or beam wind, you will appreciate how much extra work and fatique a skeg can save you. Whether the Anas Acuta really needs a skeg is a question an Anas Acuta owner will have to answer. It is true that skegs can be jammed by sand and small pebbles, but usually this can be cleared by reaching under the hull and manually moving the skeg up and down a few times. I make it a practice to test the skeg before putting in, if I can enter the boat while it is floating, or right after I put in. In the latter case, I ask a fellow paddler to unjam the skeg for me, if it is jammed. As for leakage, I haven't experienced any in my Romany's skeg after five seasons. Most, if not all, imported kayaks are shipped without footpegs installed. The Anas acuta is not unique in this regard. The footpegs are installed by the retailer as part of the package. Some people prefer to eliminate the footpegs, and install stiff foam against the forward bulkhead for bracing, but that's a matter of personal preference. Chuck Holst *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
At 11:22 AM 11/15/00 -0600, Chuck Holst wrote: > >Most, if not all, imported kayaks are shipped without footpegs installed. >The Anas acuta is not unique in this regard. The footpegs are installed by >the retailer as part of the package. Some people prefer to eliminate the >footpegs, and install stiff foam against the forward bulkhead for bracing, >but that's a matter of personal preference. I've seen a few Romany's outfitted with foam against the bulkhead rather than footpegs but I don't know about "all" imported kayaks coming without the pegs installed. All of the Seaward kayaks my friend has received at his shop have had the footpegs installed, rudder cables hooked up (where applicable) and are ready to paddle right out of the shrink wrap. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
>> I've seen a few Romany's outfitted with foam against the bulkhead rather than footpegs but I don't know about "all" imported kayaks coming without the pegs installed. All of the Seaward kayaks my friend has received at his shop have had the footpegs installed, rudder cables hooked up (where applicable) and are ready to paddle right out of the shrink wrap. >> I guess I should amend my statement to say that *Nigel Dennis* and *VCP* kayaks come with the footpegs uninstalled. :-) Chuck Holst *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Hi Kathleen, Normally when a non-engineer responds to posts like yours they usually end-up having the hats handed to them. But since no engineering types have responded, I'll offer a nontechnical response to tie you over. The cross-section of the hull determines how the boat responds to a lean by displacing water this effect is further modified by volume displacement along the length of the hull. Flatter bottomed or harder chined boats seem to have a very clear righting effect as they are leaned slightly. The force to lean them further rises sharply as the angle of lean increases. All this boils down to the perception of stability for most novices. Also most people understand this as primary or initial stability. Softer chined hulls tend to lack this strong initial stability but instead offer a smoother transition as you move from an even keel to tilting the boat. Past 10°'s or so of lean takes us into the realm of secondary stability. This is where the major differences lie. A softer chined boat may seem to have less initial stability but the secondary stability will rise smoothly up the point of capsize. Secondary stability is usually agreed to mean stability between 10° of list and the point of capsize. A hard chined boat will seem to have greater initial stability but reaches it's point of capsize more abruptly and with little notice. Hard chined boats have great appeal for many people. No doubt Melissa could be persuaded to share with you the gospel according to 'bou. Other's are equally convinced that their particular boat is, by far the best design. I am no exception, by boat is without doubt the best designed hull in all of kayakdom, and by the way it has medium chines. I do however lust after other softer chined craft from time to time. But then, after all is said and done, I'm may be a kayaker but I'm not dead so it's only natural for me to want to expand the harem, er I mean fleet. Try every boat that strikes your fancy. Let your senses and the artiste in you make the decision. Paddling is an experience for the soul, not an exercise in logical thinking. For ever point I've made someone will take issue with the science, but no-one will tell you that one and only one design is best for all people. (Except maybe Melissa, ....just kidding!) Good luck and have fun! Jed *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Speed Lump wrote: >>For ever point I've made someone will take issue with the science, but no-one will tell you that one and only one design is best for all people. (Except maybe Melissa, ....just kidding!) Good luck and have fun! Jed<< um... just for the record - I think there are many lovely boaties, and I've even paddled some of them. Of course, none of the loveliest of them have silly contraptions dangling off their sterns, etc... <melissa digs in her gear bag, looking for that flameproof wetsuit> ;-) Melissa *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Jed <LedJube_at_aol.com> wrote >>>>Normally when a non-engineer responds to posts like yours they usually end-up having the hats handed to them. But since no engineering types have responded, I'll offer a nontechnical response to tie you over. The cross-section of the hull determines how the boat responds to a lean by displacing water this effect is further modified by volume displacement along the length of the hull. So far so good Flatter bottomed or harder chined boats seem to have a very clear righting effect as they are leaned slightly. The force to lean them further rises sharply as the angle of lean increases. All this boils down to the perception of stability for most novices. Also most people understand this as primary or initial stability. Here you are confusing width below the waterline with chine. Chine is the turn of the bilge and a harder chine has the transition from bottom to side around a smaller radius. soft is more rounded. Both underwater shapes below are the same width. \ / | | \ / | | \________/ |_____________| Both are hard chined when compared to a hull more like the second one but with rounded corners. The rounded cornered hull with vertical sides will be between the first and second hulls in initial stability. This contradicts Jed's assertion that hard chines are more initially stable. Secondary stability consists of many things and I also don't have any exact definition of it, and don't believe any exact meaning of the term has been agreed upon as yet. Some FAQ's on our website http://www.marinerkayaks.com discuss one way for a kayaker to look at it. If the sides of the two hulls above (and #3 with the rounded corners) with the same waterline width continue up above the waterline at the same angle as below the waterlines the first hull with the flared sides will have the greatest secondary stability by just about anybody's perception or "feel". This contradicts what Jed just said about the more rounded hull having the better secondary stability. As far as dynamic stability (or ease of staying upright in waves) goes I'll put my money on the first shape rather than the other two. This is in fact the shape of a river dory. I want to be clear here that I'm not trying to claim the opposite of what Jed wrote just pointing out that the chine is not the determining factor in primary or secondary stability (but it can sure help dynamic stability compared to a rounded hull by decreasing the sideways skid on the face of a steep wave--as can a V-bottomed shape). >>>>>Softer chined hulls tend to lack this strong initial stability but instead offer a smoother transition as you move from an even keel to tilting the boat.<<<<< How would one show or detect a smoother transition? What should I look for on a static stability graph? All the graphs I've looked at seem to be relatively smooth. >>>>Past 10°'s or so of lean takes us into the realm of secondary stability.<<<< Has this been agreed upon somewhere and I've missed it all these years? Please let me know your source or sources for this. >>>This is where the major differences lie. A softer chined boat may seem to have less initial stability but the secondary stability will rise smoothly up the point of capsize. Secondary stability is usually agreed to mean stability between 10° of list and the point of capsize. A hard chined boat will seem to have greater initial stability but reaches it's point of capsize more abruptly and with little notice.<<<< Why do you think that? What notice does the rounder hull give you before the capsize point? They all seem quite capable of catching me by surprise. although the expectation of stability of a wide flat initially stable kayak is most likely to fake me into trusting it and not paying as much attention as I should. <SNIP> >>>>Try every boat that strikes your fancy. Let your senses and the artiste in you make the decision. Paddling is an experience for the soul, not an exercise in logical thinking. For ever point I've made someone will take issue with the science, but no-one will tell you that one and only one design is best for all people! <<<< I'll certainly agree with this (and have just stepped forward to take issue), although I was hoping someone else would save me the work. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
So far so good Matt wrote: >Here you are confusing width below the waterline with chine. Chine is the >turn of the bilge and a harder chine has the transition from bottom to side >around a smaller radius. soft is more rounded. Both underwater shapes below >are the same width. \ / | | \ / | | \________/ |_____________| >Both are hard chined when compared to a hull more like the second one but >with rounded corners. The rounded cornered hull with vertical sides will be >between the first and second hulls in initial stability. This contradicts >Jed's assertion that hard chines are more initially stable. Dead on. The same stability and stability curve can result from a chined or round bilge boat. One should not generalize from limited experience. Chines do reduce rolling periods if everything else reminas equal. >Secondary >stability consists of many things and I also don't have any exact definition >of it, and don't believe any exact meaning of the term has been agreed upon > as yet. Perhaps Jed had in mind the classic naval architecure definition of initial stability which refers to the stability range in which the metacentric height can reliably predict stability and is represented by the slope of the righting curve. "Secondary stability" for sea kayakers and canoeists seems to correspond to what naval architects sometimes call "Overall stability". I had never heard the term secondary stability until I started paddling in Canada. >>>>>Softer chined hulls tend to lack this strong initial stability but instead offer a smoother transition as you move from an even keel to tilting the boat.<<<<< >How would one show or detect a smoother transition? What should I look for >on a static stability graph? All the graphs I've looked at seem to be >relatively smooth. True enough. Some hard chined boats have very high section coefficients (i.e more boxy). They have a lot of initial stability and then the stability drops like a rock at a certain point of heel. I would sayt this kind of boat has a small "range of stability". >>>>Past 10°'s or so of lean takes us into the realm of secondary stability.<<<< >Has this been agreed upon somewhere and I've missed it all these years? >Please let me know your source or sources for this. See above on this. Some good sources for this "angle" would come from most naval architecture books (some listed in my web site). >>>>Try every boat that strikes your fancy. Let your senses and the artiste in you make the decision. Paddling is an experience for the soul, not an exercise in logical thinking. For ever point I've made someone will take issue with the science, but no-one will tell you that one and only one design is best for all people! <<<< Ahh, but one sp*ns*n fits all. :-) In any case, how a boat feels or performs does not depend upon one characteristic. Cheers, John Winters Web site address http://home.ican.net/~735769 *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Jed wrote: << Flatter bottomed or harder chined boats seem to have a very clear righting effect as they are leaned slightly. The force to lean them further rises sharply as the angle of lean increases. All this boils down to the perception of stability for most novices. Also most people understand this as primary or initial stability. >> Matt responded: <<Here you are confusing width below the waterline with chine. Chine is the snip This contradicts Jed's assertion that hard chines are more initially stable. Jed's response: Matt, I made an observation based on personal experience relative to the "feel" of one design feature versus another. Although I will never know as much about boat design as you have already forgotten, I do understand the definition of chine. My reference was to "harder chined boats" as if comparing two boats of similar design but with different chine features. I don't know if the chine is responsible for my perceptions or if it was other design issues that were packaged along with the hard chines, but my perceptions are what they are just the same. In my limited experience, harder chined boats exhibit stronger initial stability than similarly designed and dimensioned boats with softer chines. All things being equal, which of course they never can be. Matt wrote: << snip . . . . . flared sides will have the greatest secondary stability by just about anybody's perception or "feel". This contradicts what Jed just said about the more rounded hull having the better secondary stability. >> Jed's response: I certainly agree with your statement regarding the relative secondary stability of a flared hull, but that was not the issue. The original poster asked about chines only. My actual statement regarding secondary stability follows: "snip . . . . A softer chined boat may seem to have less initial stability but the secondary stability will rise smoothly up the point of capsize. . . . . snip . . . . . A hard chined boat will seem to have greater initial stability but reaches it's point of capsize more abruptly and with little notice." Again I do not attribute the effects relative to stability to the chines alone but rather to the boats that have hard chines versus boats that have softer chines. Certainly I see now, thanks to you post, that the degree of flare has the greatest effect on secondary stability. I do however maintain my perception that boats with harder chines tend to have a "notchy" feel when they are leaned aggressively. And that boats with softer chines tend to feel less "notchy". Matt wrote: <<I want to be clear here that I'm not trying to claim the opposite of what Jed wrote just pointing out that the chine is not the determining factor in primary or secondary stability (but it can sure help dynamic stability compared to a rounded hull by decreasing the sideways skid on the face of a steep wave--as can a V-bottomed shape). >> Jed asks: Matt, is it not possible to back away from the forest a bit and make some generalizations about the current commercial offerings of boats with hard chines versus boats with softer chines? Given that we are addressing this to a novice curious about researching her first boat. I understand that your post seeks to correct inaccuracies from my post, and I welcome the correction. But please remember that I was referring to complete boats not the chines themselves. Jed wrote: << Softer chined hulls tend to lack this strong initial stability but instead offer a smoother transition as you move from an even keel to tilting the boat.>> Matt wrote: << How would one show or detect a smoother transition? What should I look for on a static stability graph? All the graphs I've looked at seem to be relatively smooth. >> Jed responds: One could easily determine the rate of change of the righting force relative to the change in attitude. This then could be compared relative to similar stability data from other designs. The combined data then would allow a reasonable person to make a judgment about one design having a relatively smooth or less smooth transition of forces as the boat is tilted off an even keel. Smooth or less smooth in this case would refer to the relative steepness of the stability curves. Jed wrote: << Past 10°'s or so of lean takes us into the realm of secondary stability >> Matt wrote: << Has this been agreed upon somewhere and I've missed it all these years? Please let me know your source or sources for this. >> Jed responds: John Winters, in his essay on "Stability and Seaworthiness" offer a definition for a metacentric height. As part of that definition he refers to initial stability as stability at small angles of heel. He later refers to a small angle of heel as usually less than ten degrees. I used tranductive reasoning to (incorrectly) arrive at the definition of Initial stability as being limited to angles of heel less than 10°. I apologize to all involved for my incorrect interpretation of Mr Winter's writings. Certainly there is some range of heel that we can agree to refer to as the realm of initial stability and another range that we can agree to refer to as in the realm of secondary stability. Please tell me what these ranges are so I will not misspeak in the future. Jed *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Pardon me for stepping in here - But as a rank newbie in the ranks of kayaks - What in the heck are you all talking about? Wayne ----------- LedJube_at_aol.com wrote: > Jed wrote: > << Flatter bottomed or harder chined boats seem to > have a very clear righting effect as they are leaned slightly. The force to > lean them further rises sharply as the angle of lean increases. All this > boils down to the perception of stability for most novices. Also most people > understand this as primary or initial stability. >> > > Matt responded: > <<Here you are confusing width below the waterline with chine. Chine is the > snip This contradicts Jed's assertion that hard chines are more > initially stable. > > Jed's response: > Matt, I made an observation based on personal experience relative to the > "feel" of one design feature versus another. Although I will never know as > much about boat design as you have already forgotten, I do understand the > definition of chine. My reference was to "harder chined boats" as if > comparing two boats of similar design but with different chine features. I > don't know if the chine is responsible for my perceptions or if it was other > design issues that were packaged along with the hard chines, but my > perceptions are what they are just the same. > In my limited experience, harder chined boats exhibit stronger initial > stability than similarly designed and dimensioned boats with softer chines. > All things being equal, which of course they never can be. > > Matt wrote: > << snip . . . . . flared sides will have the greatest secondary stability by > just about > anybody's perception or "feel". This contradicts what Jed just said about > the more rounded hull having the better secondary stability. >> > > Jed's response: > I certainly agree with your statement regarding the relative secondary > stability of a flared hull, but that was not the issue. The original poster > asked about chines only. My actual statement regarding secondary stability > follows: > "snip . . . . A softer chined boat may seem to > > have less initial stability but the secondary stability will rise smoothly up > > the point of capsize. . . . . snip . . . . . A hard chined boat will seem > > to have greater initial stability but reaches it's point of capsize more > > abruptly and with little notice." > > Again I do not attribute the effects relative to stability to the chines > alone but rather to the boats that have hard chines versus boats that have > softer chines. Certainly I see now, thanks to you post, that the degree of > flare has the greatest effect on secondary stability. I do however maintain > my perception that boats with harder chines tend to have a "notchy" feel when > they are leaned aggressively. And that boats with softer chines tend to feel > less "notchy". > > Matt wrote: > <<I want to be clear here that I'm not trying to claim > the opposite of what Jed wrote just pointing out that the chine is not the > determining factor in primary or secondary stability (but it can sure help > dynamic stability compared to a rounded hull by decreasing the sideways skid > on the face of a steep wave--as can a V-bottomed shape). >> > > Jed asks: > Matt, is it not possible to back away from the forest a bit and make some > generalizations about the current commercial offerings of boats with hard > chines versus boats with softer chines? Given that we are addressing this to > a novice curious about researching her first boat. > I understand that your post seeks to correct inaccuracies from my post, > and I welcome the correction. But please remember that I was referring to > complete boats not the chines themselves. > > Jed wrote: > << Softer chined hulls tend to lack this strong initial stability but > instead offer a smoother transition as you move from an even keel to tilting > the boat.>> > > Matt wrote: > << How would one show or detect a smoother transition? What should I look for > on a static stability graph? All the graphs I've looked at seem to be > relatively smooth. >> > > Jed responds: > One could easily determine the rate of change of the righting force > relative to the change in attitude. This then could be compared relative to > similar stability data from other designs. The combined data then would allow > a reasonable person to make a judgment about one design having a relatively > smooth or less smooth transition of forces as the boat is tilted off an even > keel. Smooth or less smooth in this case would refer to the relative > steepness of the stability curves. > > Jed wrote: > << Past 10°'s or so of lean takes us into the realm of secondary stability >> > > Matt wrote: > << Has this been agreed upon somewhere and I've missed it all these years? > Please let me know your source or sources for this. >> > > Jed responds: > John Winters, in his essay on "Stability and Seaworthiness" offer a > definition for a metacentric height. As part of that definition he refers to > initial stability as stability at small angles of heel. He later refers to a > small angle of heel as usually less than ten degrees. > I used tranductive reasoning to (incorrectly) arrive at the definition of > Initial stability as being limited to angles of heel less than 10°. I > apologize to all involved for my incorrect interpretation of Mr Winter's > writings. Certainly there is some range of heel that we can agree to refer to > as the realm of initial stability and another range that we can agree to > refer to as in the realm of secondary stability. Please tell me what these > ranges are so I will not misspeak in the future. > > Jed > > *************************************************************************** > PaddleWise Paddling Mailing List - Any opinions or suggestions expressed > here are solely those of the writer(s). You must assume the entire > responsibility for reliance upon them. All postings copyright the author. > Submissions: PaddleWise_at_PaddleWise.net > Subscriptions: PaddleWise-request_at_PaddleWise.net > Website: http://www.paddlewise.net/ > *************************************************************************** -- Wayne Smith http://www.waynesmith.net/weight 07 October 1999 - 315 lb. - Dr Rumbaut - Monterrey, Mexico --------------------------------------------------- Tag Line for Today: ERROR: Are you *really* trying 9600bps? Tsk, tsk... --------------------------------------------------- *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. 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Oh my, there are two of us with the same name here! Less confusing than at work, where there are 5 Wayne Smiths, I guess. But to answer your question, they're talking about hull shapes --- a more "boxy" shape being classified as "Hard Chined" and a more rounded shape being classified as "Soft Chined". Regards, The other Wayne Smith Wayne Smith wrote: > Pardon me for stepping in here - But as a rank newbie in the ranks of kayaks - > What in the heck are you all talking about? > > Wayne > ----------- -- -------------------------------------------------------------------------------- Wayne Smith wsmith16_at_snet.net Check out my sea kayaking & homebrewing page: http://pages.cthome.net/wsmith16/home.html *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Jed wrote; Jed wrote: << Past 10°'s or so of lean takes us into the realm of secondary stability >> Matt wrote: << Has this been agreed upon somewhere and I've missed it all these years? Please let me know your source or sources for this. >> >Jed responds: > John Winters, in his essay on "Stability and Seaworthiness" offer a >definition for a metacentric height. As part of that definition he refers to >initial stability as stability at small angles of heel. He later refers to a >small angle of heel as usually less than ten degrees. > I used tranductive reasoning to (incorrectly) arrive at the definition of >Initial stability as being limited to angles of heel less than 10°. I >apologize to all involved for my incorrect interpretation of Mr Winter's >writings. Certainly there is some range of heel that we can agree to refer to >as the realm of initial stability and another range that we can agree to >refer to as in the realm of secondary stability. Please tell me what these >ranges are so I will not misspeak in the future. Jed, you got it right enough if the naval architecture books I studied and the naval architects I worked with over the years know anything at all. In the past people have asked for a list of my sources assuming, I suppose, that I make this stuff up as I go. To head this off at the pass try the following; Principles of Naval Architecture" by the Society of Naval Architects and Marine Engineers ( I have some partiality to this one since I belong to this august body. Hey, don't ask why they would want me, it still amazes me.) Introduction to Naval Architecture by Thomas Gilmer (text book used by the U.S. Naval Academy) Basic Ship Theory byRawson and Tupper Seaworthiness: The Forgotten Factor by C. J. Marchaj Cheers, John Winters Web site address http://home.ican.net/~735769 *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
In a message dated 11/11/00 1:25:51 AM !!!First Boot!!!, wsmith16_at_snet.net writes: << But to answer your question, they're talking about hull shapes --- a more "boxy" shape being classified as "Hard Chined" and a more rounded shape being classified as "Soft Chined". >> And just to add a little more ink to the water, let us not forget the trihedral which would fall under the category of multi-chined(?). Bruce McC WEO *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Will the real Wayne Smith stand up? One Wayne Smith wrote: > Oh my, there are two of us with the same name here! Less confusing than at work, > where there are 5 Wayne Smiths, I guess. > > But to answer your question, they're talking about hull shapes --- a more "boxy" > shape being classified as "Hard Chined" and a more rounded shape being classified > as "Soft Chined". > Bring out the nit pickers and strike a blow for pedantry. Not really. Hard chine boats have a distinct intersection between sides and hull bottom that meets with a "sharp" edge. A "soft" chine boat has a rounded intersection and a round bilge boat has no clearly defined transition from bottom to side the most extreme example being a perfectly round section. Gilmer defines it this way: "A more or less sharp corner or knuckle in the hull form, continuous over a significant length of the ship, as in the junction of side and bottom of a planing craft. The chine is known as soft when the corner is rounded, and hard otherwise" Who is Gilmer? The past head of the school of Naval Architecture at the U.S. Naval Academy. Some time back we had a discussion about sheer lines. Where is the sheer on a boat with a rounded edge? This problem has plagued yacht racing rule writers and well as those who measure and license ships. The method they use is to define the sheer as a line formed by a forty-five degree tangent to the hull/deck surface. Wish I had thought of it as it rather elegantly lends clarity to something boat designers have puzzled over. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Jed wrote: >>>>I do however maintain my perception that boats with harder chines tend to have a "notchy" feel when they are leaned aggressively. And that boats with softer chines tend to feel less "notchy".<<<<< Please define "notchy". I've seen at least one hundred stability graphs (for both round and hard chine kayaks) and have yet to see one that isn't a fairly continuous curve without sudden changes except sometimes near the "peak" (the point of maximum righting moment). Which boats are you comparing? Which ones) feel "notchy"? I'm much more comfortable comparing specific trees than trying to make sense of the forest. Jed asks: >>>>>>Matt, is it not possible to back away from the forest a bit and make some generalizations about the current commercial offerings of boats with hard chines versus boats with softer chines? Given that we are addressing this to a novice curious about researching her first boat. I understand that your post seeks to correct inaccuracies from my post, and I welcome the correction. But please remember that I was referring to complete boats not the chines themselves.<<<<< Since there are hundreds of current offerings covering a wide range of the possible spectrum in cross sectional shape limiting the discussion to current offerings doesn't get nearly specific enough. If you would like to get real specific and tell us the kayaks you find these differences in I might be able to account for them because of other reasons besides the differences in hardness of the chine. You can't make generalizations that would be helpful to a novice here (if one ever can) because, as I tried to point out, other variables overwhelm the one you want to generalize about. Even trying to say "if everything else is equal" won't work here because everything else can't be equal here and whichever characteristics you make equal will both effect the outcome and still probably allow exceptions to the generalization. Therefore a generalization here will only lead a novice astray, and in the worst possible way, by believing something that is not true. Much better to know you are ignorant and try the kayaks for yourself. >>>>>>>Matt wrote: <<<<<<< How would one show or detect a smoother transition? What should I look for on a static stability graph? All the graphs I've looked at seem to be relatively smooth. >> >>>>Jed responds: >>>>One could easily determine the rate of change of the righting force relative to the change in attitude. This then could be compared relative to similar stability data from other designs. The combined data then would allow a reasonable person to make a judgment about one design having a relatively smooth or less smooth transition of forces as the boat is tilted off an even keel. Smooth or less smooth in this case would refer to the relative steepness of the stability curves.<<<<<<<< This is what is done. It is known as the "static stability curve" and you can see the results for many kayaks in Sea Kayaker magazine's kayak reviews. Hard chine or soft chine, the curves look very similar to me. I don't think, even after studying them closely, I could pick out a hard chine boat from a soft chine one based only on looking at the static stability curves unless I also had more data on the kayaks. John Winters wrote: >>>>>Perhaps Jed had in mind the classic naval architecure definition of initial stability which refers to the stability range in which the metacentric height can reliably predict stability and is represented by the slope of the righting curve. "Secondary stability" for sea kayakers and canoeists seems to correspond to what naval architects sometimes call "Overall stability". I had never heard the term secondary stability until I started paddling in Canada.<<<<< I am in full agreement with the definitions of initial stability made by John and the naval architecture texts. A good definition of secondary stability is what has eluded me. It appears to be a paddlers term not a Naval Architects term. However, good paddlers know it when they feel it. It is my experience that what the paddler senses doesn't correlate at all well with "overall stability". I think I can spot it on a static stability curve by looking at the lean angle at the peak of the curve or the point where it breaks most sharply near the peak (see curve for the Pisces in the XL review for an example of what I mean). The larger the lean angle is at the peak of the curve (or the break point) the more likely that kayak will be described as having good secondary stability by a kayaker willing to test the limits of stability to the point of capsize. The amount of righting force at the peak does not correlate well with subjective reports and, in fact, too high a righting force can work against the feeling of good secondary stability. Ever try to open a stuck door or drawer gently, without going too far once it finally comes unstuck. Similar kind of thing. John wrote: >>>>>True enough. Some hard chine boats have very high section coefficients (i.e more boxy). They have a lot of initial stability and then the stability drops like a rock at a certain point of heel. I would sayt this kind of boat has a small "range of stability".<<<<< I think this "drops like a rock" point may have more to do with the height of the deck than the shape of the bottom. The stability curve generally peaks about the time the deck starts to submerge during a lean. This makes sense because the buoyancy most helping support the lean (at the widest point) is then fully under the water with no reserve left to counteract more lean. A higher hull will be able to lean further than a lower hull before this happens. Of course if the low hull also has hard chines one might think the chines were responsible for reaching the point of maximum stability at a lesser angle. Alternately if both kayaks were wide enough then the increased initial stability resulting from a more box like hull (higher midship section coefficient) may be enough extra stability to make the lean difficult and result in your drawers suddenly coming unstuck (as you fill them with lubrication and capsize;-). Note: taken to the extreme a boxier shape will result in a harder chine but a hard chine can also exist on a low midship sectional coefficient hull as well if it is combined with something like flare to the sides of the hull). (2nd note: the midship section coefficient is the ratio of area of the shape of the boat underwater at the cross-sectional plane at the widest waterline beam with the area of a rectangle as wide as the waterline beam and as deep as the draft. For a rectangular box it would be 1/1=1.00, a V bottom triangular hull would be .50, a semicircular hull would be pi/4=.7865). The capsize point is defined as where the righting moment drops to zero but if one leans beyond the point of maximum stability ones momentum can also quickly take one past the capsize point (as if the rug of increasing stability with further lean has been suddenly pulled out from under you, or the stability drawer came unstuck). The Sea Kayaker Magazine Review of the Mariner XL on our website http://www.marinerkayaks.com has a very good discussion at the end to help the reader determine the significance of the stability graphs. A strictly personal interpretation of "kayaker perceived secondary stability" exists in the FAQ's of our website. Sorry about the messed up diagrams in the last post. All I can say is they looked okay when I pushed the send button. Jackie how do you get your drawings to hang together? I'm definitely a newby at drawing using keyboard characters. Do you have any generalizations that could help me next time I try? Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. 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Matt wrote - >I think I can spot it on a static stability curve >by looking at the lean angle at the peak of the curve or the point where it >breaks most sharply near the peak (see curve for the Pisces in the XL review >for an example of what I mean). The larger the lean angle is at the peak of >the curve (or the break point) the more likely that kayak will be described >as having good secondary stability by a kayaker willing to test the limits >of stability to the point of capsize. By that do you mean the flatter the peak the more "secondary stability" (not having the Pices curve handy at present)? I suppose one point to really emphasis to everyone is steepness (or not) of curve, not total height that we're talking about. Alex . . Alex (Sandy) Ferguson Chemistry Department University of Canterbury New Zealand *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Alex wrote: > By that do you mean the flatter the peak the more "secondary stability" > (not having the Pices curve handy at present)? > > I suppose one point to really emphasis to everyone is steepness (or not) of > curve, not total height that we're talking about. Secondary stability has to do with both the range of stability (how far the boat can heel before it reaches vanishing righting moment, the total area under the righting moment or righting arm curve, the maximum righting moment, the slope(s) of the curve and the location of the maximum righting moment (or arm). The greater the range of stability the more heel one can experience and still have some righting force. The greater the total area under the curve the greater the righting force sensed over the full range of heel. The higher the maximum righting moment (or arm) the greater the sensation of righting force at that particular point. The location of the maximum tells when (at what heel) you will feel that maximum force. The slope of the curve at any point tells how rapidly the righting force changes with a change in heel. If one paddles a number of boats and compares their curves and how the boats feel then it becomes possible to look at a curve and get a mental picture of its stability characteristics. No one type of stability will suit all paddling needs or preferences although (from my experience) a large range of stability, a smooth parabolic stability curve, with its maximum roughly at or just past the angle that one can easily lean the body seems to appeal to most people. Clearly because people differ, no one curve shape will fit all. The thing that I find most objectionable (once again in my experience) has to do with the sensation of rapidly changing stability revealed by steep curve slopes on either side of the stability curve. Cheers, John Winters Web site address http://home.ican.net/~735769 *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Alex Ferguson <a.ferguson_at_chem.canterbury.ac.nz> wrote: >>>>Matt wrote - >I think I can spot it on a static stability curve >by looking at the lean angle at the peak of the curve or the point where it >breaks most sharply near the peak (see curve for the Pisces in the XL review >for an example of what I mean). The larger the lean angle is at the peak of >the curve (or the break point) the more likely that kayak will be described >as having good secondary stability by a kayaker willing to test the limits >of stability to the point of capsize. By that do you mean the flatter the peak the more "secondary stability" (not having the Pices curve handy at present)? I suppose one point to really emphasis to everyone is steepness (or not) of curve, not total height that we're talking about.<<<<<<< You won't get high on this curve without also going steeply up. I didn't word that quoted passage very well. What I meant to get across was that the further the kayak could be leaned before reaching maximum stability the more likely an expert kayaker would say it had good secondary stability. By my definition even a very unstable kayak can have good secondary stability as long as the point of maximum stability is shifted enough to the right that a kayaker can't easily lean the kayak beyond it. This is far different than the "overall stability" (the total energy required to cause a capsize) which can be measured by measuring the area under the curve. This feeling of secondary or final stability to a kayaker takes in to consideration that the kayaker wants to intentionally lean her craft. Low initial stability allows this to be done easily so there is no big hump that has to be overcome to get the kayak leaned to there but an even further lean would be resisted by a still increasing righting force. Once beyond the peak righting force it is hard to stop a capsize because each degree further you lean the less the stability becomes. The original stability curves Sea Kayaker's John Dawson did back in 1986 were done with a torque wrench (now sea Kayaker models this with a computer program). Interestingly the testers quickly learned that the only way they could measure the righting force on the downhill or "backside" of the curve was by starting at the capsize point and working backwards up the curve taking measurements as the kayak came more upright. If they moved from left to right along the curve (closer to capsize) just the slight added force moving the kayak closer to the capsize point once it reached the peak would throw the boat over into an immediate capsize This happened even when they were trying to be as gentle as possible with the torque wrench. For that reason I think one can pretty much ignore the shape of the curve past its peak (for any feeling of static stability anyhow). Of course a kayaker/kayak combo isn't static and by shifting the center of gravity (by bending at the waist) a greater angle of lean can be achieved in the kayak before reaching the maximum righting moment. To adequately discover how a kayak will react to this common situation we would probably need to shift the center of gravity over (to where a good kayaker could shift it) in our "model" and look at the new curve that results then. Maybe I'll suggest this to Sea Kayaker it might be informative to do this with the test kayaks. John has the same program Sea Kayaker uses maybe he can try it out for us with some of the kayaks he has gotten measurements for. The Pisces curve can be found on the XL review from Sea Kayaker (that I got permission to put on my website www.marinerkayaks.com). What is interesting about the Pisces curve is that it climbs fairly steeply, has a break but then still climbs at a much more gradual angle for awhile before reaching its peak. It isn't entirely clear to me but that break might actually be the real beginning of the unstable "backside" range because the rate of increase drops off so suddenly after the break. That was why I was using the stuck drawer analogy earlier (and the bump on the rockers of a rocking chair in the FAQ's about stability on our website. Imagine someone trying to roll a ball bearing up ramp the shape of that curve. I think they would find that if the ball bearing made it up the steep slope and over the break that more likely than not it would also continue on all the way over the shallow peak and that it would be very difficult to give the ball bearing just the right momentum to get it over the transition but not also over the top. The marble would be much easier to get over the top of the shallower curve from a tippy kayak but it could also be much more likely to get further to the right (more tilt) and return back down the front again (more predictably) than it would with the steeper ramp with an earlier rapid change in angle in it (like the Pisces). Maybe this sudden transition from hard to lean to easy to lean further is what Jed means by "notchy". I do not think any sudden changes on the back side of the curve would contribute to notchiness though, as John postulates, because once you have forced yourself over the peak (of a steep high curve anyhow) the recently unstuck drawer is probably going to fall out of the chest and spill all your clean underwear onto that floor you didn't clean because you went kayaking instead. Of course if the static curves "backside" notch is no longer over the top because the kayaker has bent at the waist and shifts his center of gravity then a quick transition that had been on the "backside" could be shifted forward to suddenly withdraw the support you needed. There, in trying to explain what I really meant I have probably confused things even more. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Matt Broze wrote: > I didn't word that quoted passage very well. What I meant to get across was > that the further the kayak could be leaned before reaching maximum stability > the more likely an expert kayaker would say it had good secondary stability. > By my definition even a very unstable kayak can have good secondary > stability as long as the point of maximum stability is shifted enough to the > right that a kayaker can't easily lean the kayak beyond it. This is far > different than the "overall stability" (the total energy required to cause a > capsize) which can be measured by measuring the area under the curve. This > feeling of secondary or final stability to a kayaker takes in to > consideration that the kayaker wants to intentionally lean her craft. Low > initial stability allows this to be done easily so there is no big hump that > has to be overcome to get the kayak leaned to there but an even further lean > would be resisted by a still increasing righting force. > > Once beyond the peak righting force it is hard to stop a capsize because > each degree further you lean the less the stability becomes. Secondary stability means different things to different paddlers and, Matt, your description really sheds a lot of light on this. As far as I can tell, secondary stability is something that a better paddler can take advantage of for sculling, leaned turns etc. But it would be a mistake for a less able paddler to think he or she has some level of stability that will kick in to keep them upright after they move from initial stability to this "secondary" stage. It really is only there if you have the abilities. In a part that I snipped from your writeup, you wondered out loud whether Sea Kayaker might want to add a component to the stability curves that reflects what a more expert paddler would do with his or her body to control the boat at this secondary stability stage. Your thought on that underlines how closely related the "stability" of the secondary stage is to the actions/skills of the paddler. ralph diaz -- ----------------------------------------------------------------------- Ralph Diaz . . . Folding Kayaker newsletter PO Box 0754, New York, NY 10024 Tel: 212-724-5069; E-mail: rdiaz_at_ix.netcom.com "Where's your sea kayak?"----"It's in the bag." ----------------------------------------------------------------------- *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Matt wrote in response to Alex: > > You won't get high on this curve without also going steeply up. > I didn't word that quoted passage very well. What I meant to get across was > that the further the kayak could be leaned before reaching maximum stability > the more likely an expert kayaker would say it had good secondary stability. > By my definition even a very unstable kayak can have good secondary > stability as long as the point of maximum stability is shifted enough to the > right that a kayaker can't easily lean the kayak beyond it. This is far > different than the "overall stability" (the total energy required to cause a > capsize) which can be measured by measuring the area under the curve. Maybe I should help clear this up. The area under the curve does not constitute the totality of "overall stability". As I mentioned in an earlier post overall stability includes the area under the curve, the slopes of the curve, the range of stability and the location of maximum righting force or moment. All combine to provide what we sense as overall stability or secondary stability. Naval architects do not have a single measure of overall stability but utilize all factors. >This > feeling of secondary or final stability to a kayaker takes in to > consideration that the kayaker wants to intentionally lean her craft. Low > initial stability allows this to be done easily so there is no big hump that > has to be overcome to get the kayak leaned to there but an even further lean > would be resisted by a still increasing righting force. I would not include the kayaker's objectives as a measure or yardstick of secondary stability. If we do then secondary stability becomes "what we say it is" and has no meaning. (SNIP) >To adequately discover how a kayak will react to > this common situation we would probably need to shift the center of gravity > over (to where a good kayaker could shift it) in our "model" and look at the > new curve that results then. Maybe I'll suggest this to Sea Kayaker it might > be informative to do this with the test kayaks. John has the same program > Sea Kayaker uses maybe he can try it out for us with some of the kayaks he > has gotten measurements for. This is precisely what happens when the person leans to resist heel. I discussed this in my article in Sea Kayaker to explain why a boat with negative static stability could remain upright. By plotting the stability curve for shifts in weight (commonly done for ships) on finds out how the boat will react to a wide range of conditions. Fortunately the shape of the stability curve does not change radically on kayaks and one can simply raise and shift the curve to the right to see what happens. This reveals why a shallow slope on the "back" side of the curve can impart a greater sense of security to some paddlers since it provides more righting force to slow the capsize. >I think they would find that > if the ball bearing made it up the steep slope and over the break that more > likely than not it would also continue on all the way over the shallow peak > and that it would be very difficult to give the ball bearing just the right > momentum to get it over the transition but not also over the top. The marble > would be much easier to get over the top of the shallower curve from a tippy > kayak but it could also be much more likely to get further to the right > (more tilt) and return back down the front again (more predictably) than it > would with the steeper ramp with an earlier rapid change in angle in it > (like the Pisces). Maybe this sudden transition from hard to lean to easy to > lean further is what Jed means by "notchy". We could also apply the ball bearing analogy to the speed of capsize by comparing the velocity of the ball bearing rolling down the gradual slope of the backside of the curve with the more rapid acceleration of the bearing rolling down a steep slope. One way of looking at it that may help is to ask how much righting force do you have to provide to keep the boat upright at each angle of heel. If the slope drops rather steeply you have to provide more for every additional degree of heel than for a boat with a shallow slope. One might not notice it when up to the armpits in water but it still applies. > I do not think any sudden changes on the back side of the curve would > contribute to notchiness though, as John postulates, because once you have > forced yourself over the peak (of a steep high curve anyhow) the recently > unstuck drawer is probably going to fall out of the chest and spill all your > clean underwear onto that floor you didn't clean because you went kayaking > instead. Of course if the static curves "backside" notch is no longer over > the top because the kayaker has bent at the waist and shifts his center of > gravity then a quick transition that had been on the "backside" could be > shifted forward to suddenly withdraw the support you needed. True if you "force yourself" over the maximum righting arm because you are trying to attain a capsize by forcing yourself past the maximum righting arm. However, most people will try to resist the capsize and the righting force obtained from a brace or body shift combines with the righting arm of the hull to act towards righting the boat. The greater the righting force past the maximum righting moment the less force one needs to exert to return the boat to an upright position. Because the righting force involves both the boat and paddler we need to look at the system rather than the individual components. One of the most challenging aspects of discussing stability comes from trying to verbalize perceptions. We "feel" stability and unless one has experienced a lot of boats and related that experience to the static stability curves they (the curves) make little sense or have little value. In looking back over the related posts I feel like everyone has it "right" within the context of their experience. Few of us have the luxury of matching that experience to a full range of stability studies and we draw our conclusions on the information we have. Cheers, John Winters *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
On Wed 15 Nov 2000, 735769 wrote: snip > However, most people will try to resist the capsize and the righting force > obtained from a brace or body shift combines with the righting arm of the > hull to act towards righting the boat. The greater the righting force past > the maximum > righting moment the less force one needs to exert to return the boat to an > upright position. Because the righting force involves both the boat and > paddler we need to look at the system rather than the individual components. So if I'm designing a boat for an individual that is going to definately expect to catch most instability events with a strong brace (even at extreme angles), then I want to design in a smoother roll off of the righting force, so as to provide an easier catch for this specific set of individuals. I have always been a little shy of understanding why an expert paddler wants such a damn tippy boat. Now I think I understand, or at least I've found another piece of the puzzle. The best explaination of "why a tippy boat?", has always been that they are actually less tippy when negotiating step waves. But I never completed believed this, and presumed even with solid athleticism you would be better off with (given relatively the same shape) a 22in+ boat than a 20-21.5in 18ft boat. Now I see an important part of the trade-off is easier catch versus less stability. So if I'm right about this the chine discussion has helped to identify some of the strengths of the "tippy boat" for me, but I'm still at quite a loss for understanding why you would want a hard chined boat. It has been said that the hard chines do a better job of resisting skid. I would add that for this skid resistance there is a price paid in reduced stability. As a hard chined boat like the looksha (only hard chined boat I've paddled), is leaned, you reach something of a discontinuity in the righting force curve and at that point you sort of flop on to a side plane of the boat. So if a missed stroke and blast of wind or water combine to cause a rotational moment towards capsize, in the critical first few hundred milliseconds of time (and before you execute your brace), a smooth chined boat will be steadily applying more righting force which will serve to decelerate the rotational velocity and reduce rotational momentum... ...whereas a hard chined boat would hit that discontinuity in stability which I spoke of. At that point the righting force would more or less vanish and the decelerating force would vanish along with it. Since in a soft chined boat the decelerating force would not vanish, it can be said, that relatively speaking, the hard chined boat will act to apply an accelerating force towards, you guessed it, capsize. That doesn't sound like a good trade-off to me. Even those damn tippy boats wouldn't do that. This is all arm chair postulating from a nonexpert, so take it with a grain of salt. But for now, this is my perspective. -- Mike McNally mmcnally3_at_prodigy.net *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
John Winters wrote: >>>>>No one type of stability will suit all paddling needs or preferences although (from my experience) a large range of stability, a smooth parabolic stability curve, with its maximum roughly at or just past the angle that one can easily lean the body seems to appeal to most people.<<<< I like this better than what I just wrote. It even leaves room for individuals varying preferences. I especially like the part about the preference for maximum being just beyond the angle that the paddler feels comfortable (I might add--leaning without a bracing stroke). If that maximum point were to be moved too far to the right one would just be losing a steeper angle (better stability) to the curve to increase the angle of leaning the kayak at the maximum righting moment (putting the maximum in a range where few folks will ever use it and making the kayak less stable for no good reason). At least with relatively shallow stability curves, it's better to increase the rate of picking up the stability as much as can be done without making it too easy for an expert to go beyond the maximum righting moment. If however the stability curves are relatively steep on the front face it would be better to shallow that curve out by moving the maximum righting moment to a greater angle of lean, reducing initial stability. That way the kayak won't be too hard to lean when you want too (and possibly causing you to drop your drawers while trying to lean;-). Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
John Winters wrote: <SNIP> >>>>Maybe I should help clear this up. The area under the curve does not constitute the totality of "overall stability". As I mentioned in an earlier post overall stability includes the area under the curve, the slopes of the curve, the range of stability and the location of maximum righting force or moment. All combine to provide what we sense as overall stability or secondary stability. Naval architects do not have a single measure of overall stability but utilize all factors.<<< Just how much weight do they assign to each of these factors (and are these factors all that need to be included in "overall stability") or is this overall also somewhat subjective? Where is "overall stability" also called "secondary stability" in Naval Architecture literature? I've not seen this before now (and if I remember correctly earlier in this thread you wrote you hadn't encountered the term "secondary stability" until you had became a paddler in Canada--or something like that). If they aren't defined as the same thing somewhere (that we can agree is the last word on the subject) then why not use the term "overall stability" as defined and forget trying to make "secondary stability" also have the same (apparently vague) meaning. Isn't one word enough? I wrote: >This feeling of secondary or final stability to a kayaker takes in to > consideration that the kayaker wants to intentionally lean her craft. Low > initial stability allows this to be done easily so there is no big hump that > has to be overcome to get the kayak leaned to there but an even further lean > would be resisted by a still increasing righting force. John responded: >>>I would not include the kayaker's objectives as a measure or yardstick of secondary stability. If we do then secondary stability becomes "what we say it is" and has no meaning.<<< That may well be why the term "secondary stability" apparently isn't defined in Naval Architecture. It seems to be subjective and relates to a feeling of security one has while leaned (not necessarily an easily measured thing). We all have our own feel for it and it has meaning for us but for lack of a clear definition it has no universal or agreed on precise meaning. I'm trying to apply what I feel with what I see on the stability curves so I might interpret them better. (SNIP) John wrote: >>>True if you "force yourself" over the maximum righting arm because you are trying to attain a capsize by forcing yourself past the maximum righting arm. <<< One need not be trying to capsize to accidentally force oneself beyond the point where the righting force is suddenly disappearing so fast in front of the lean angle that there isn't time to recover. Too much initial stability makes it hard to get the kayak to lean and once leaned much past the point of maximum stability it becomes a balancing act to ride the fine edge between the point where you don't have to work too hard to keep the kayak leaned and where you have gone over to the "Backside" and might be baptized before you can return. Using the analogy of the standard chair vs. the rocking chair that I used on the stability FAQ's on our website. Here I'll save myself rewriting it and just copy the relevant part for you: I'll make an analogy with rocking back in a rocking chair (low initial stability/higher secondary stability) and compare that to rocking back in a regular four legged chair (high initial stability/high total stability/low feeling of security as you teeter at the balance point). It is hard to lean back on a standard chair (most of my teachers frowned on my practice of balancing my desks on the back legs when I was bored, especially when I would draw their attention to what I was doing when I would almost lose my balance backwards and --in a desperate attempt to recover--crash back down loudly to the "initially" stable position. I don't remember ever going over backwards but that was always the risk I flirted with--a capsize to the rear). Looking at the static stability graphs I would define a kayak with good secondary stability as one whose stability curves show a relatively shallow angle off of zero (so you don't have to put a lot of energy into leaning it) but which has the point of maximum stability (the top of the curve) at a greater angle of lean (and maybe, but not necessarily, at a higher maximum point) than a kayak with less "secondary" stability. (See the Mariner XL, Arluk III, and Solander stability comparisons in the XL review in the Spring 1987 issue of Sea Kayaker magazine). [note: this comparison can be seen in the "reviews" section of www.marinerkayaks.com] Even this doesn't totally account for the difference in "feel". A smooth progressive increase in stability out to near the maximum allows a trustworthy "feel". Any abrupt changes would be like putting a speed bump or flat spot on the rocking chair rockers. The above definition is from my own observations and guesses regarding secondary stability in kayaks. I make no claim to scientific validity or even at a valid definition of the term (which may exist somewhere in Naval Architecture). I and most experienced paddlers prefer lower initial and good "secondary" stability. Easy to lean yet secure while leaned. End of FAQ from website-------------- John continued: >>>However, most people will try to resist the capsize and the righting force obtained from a brace or body shift combines with the righting arm of the hull to act towards righting the boat. The greater the righting force past the maximum righting moment the less force one needs to exert to return the boat to an upright position. Because the righting force involves both the boat and paddler we need to look at the system rather than the individual components.<<< While what you say is true, I think it gives a wrong impression about what we need to look at here since the power of a brace can be so much stronger than the righting force it combines with that it renders the righting force part of the system almost meaningless in comparison. This also doesn't take into account our nervous system's feedback delay that slows the paddlers reaction time. I think the effort it takes to get a very stable kayak up to the point where that leaning effort can be somewhat relaxed (now on the "backs(l)ide") leaves the paddler in a precarious position, hanging out over the water as a counterbalance to the kayaks stability and dependent on his paddle and the security of the kneebrace to prevent a capsize that is only a few degrees, a moment on inattention, and a little momentum away. Imagine you are arm wrestling with an opponent you only want to tie (like your strong child maybe) and he suddenly relaxes. The delay in your nervous system will not allow you to slack off at exactly the same time as your opponents relaxation so you are going to move his hand further than you had intended (and also further than if you had been pushing a lot less hard to begin with--an analogy for initially less stable). This nervous system delay and the suddenness with which a capsize can occur when the resisting force drops away in front of the lean means the paddler either can't lean that wide gear laden kayak much at all or if he does, he risks going too far over before his reaction time forces him to need a quick brace to prevent a capsize. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Matt wrote: (SNIP) > > Just how much weight do they assign to each of these factors (and are these > factors all that need to be included in "overall stability") or is this > overall also somewhat subjective? Don't know of anything else. > Where is "overall stability" also called "secondary stability" in Naval > Architecture literature? I've not seen this before now (and if I remember > correctly earlier in this thread you wrote you hadn't encountered the term > "secondary stability" until you had became a paddler in Canada--or something > like that). I believe Steven Killing refers to it a secondary stability (I will check on that) but he is a Canadian designer so what doe she know. :-) Other than that i know of no other place where it is called "secondary stability". Since what people call "secondary stability" seems to correspond to what naval architects call "Overall stability" it seems like one and the same thing. > If they aren't defined as the same thing somewhere (that we can agree is the > last word on the subject) then why not use the term "overall stability" as > defined and forget trying to make "secondary stability" also have the same > (apparently vague) meaning. Isn't one word enough? You bet. (SNIP) > > John responded: > >>>I would not include the kayaker's objectives as a measure or yardstick of > secondary stability. If we do then secondary stability becomes "what we say > it is" and has no meaning.<<< > > That may well be why the term "secondary stability" apparently isn't defined > in Naval Architecture. It seems to be subjective and relates to a feeling of > security one has while leaned (not necessarily an easily measured thing). We > all have our own feel for it and it has meaning for us but for lack of a > clear definition it has no universal or agreed on precise meaning. I'm > trying to apply what I feel with what I see on the stability curves so I > might interpret them better. That indeed seems to form the crux of the problem. I encourage people to paddle a numbe of different boats and compare the satbility curves. This helps me get a better idea of what they mean when they say "good" or "bad" overall stability. (From this day forward I shall not use the "S" word stability) (SNIP) > > While what you say is true, I think it gives a wrong impression about what > we need to look at here since the power of a brace can be so much stronger > than the righting force it combines with that it renders the righting force > part of the system almost meaningless in comparison. This also doesn't take > into account our nervous system's feedback delay that slows the paddlers > reaction time. I don't have any data to support "meaningless" and would suggest that if peope can sense the stability of the boat then it probably exceeds "meaningless". What do they sense if not the boat? > > I think the effort it takes to get a very stable kayak up to the point where > that leaning effort can be somewhat relaxed (now on the "backs(l)ide") > leaves the paddler in a precarious position, hanging out over the water as a > counterbalance to the kayaks stability and dependent on his paddle and the > security of the kneebrace to prevent a capsize that is only a few degrees, a > moment on inattention, and a little momentum away. True and I think this is what Alex tried to say when he mentioned the slope of the stability curve. Correct me if I got that wrong, Alex. I don't know what the paddler senses other than the physical forces of stability acting on the boat. We can quantify those forces and while they don't come in a nice neat single number we can look at the package and relate that to what we sense. Maybe this will help. The righting moment includes both he paddler's body weight shift, the effect of the boat's shape, and the forces generated by the paddle(if any). The righting force after the hull's maximum is additive. That is, boat righting arm plus weight shift plus paddle forces. The greater the righting moment contributed by the boat after the maximum the less on needs of the other two to right the boat. Clearly the less one needs to do to keep the boat upright the more stable it seems. So, if one righting moment curve is higher after the maximum than another (shallower slope) then the paddler will perceive it as having more stability. Using Matt's arm wrestling analogy one could say that it is a bit like the opponent slowly reducing his effort rather than relaxing completely. Cheers, John Winters *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Dear Matt, John and all, It might be that Navel Architecture does not consider and define "secondary stability", as John points out, because it is not relevant to the vast majority of vessels. Only in kayaks and perhaps smaller canoes can one even perceive such a phenomena since you more or less wear the kayak and control it by twists and shifts of your body. In an ocean liner or freighter no one can feel secondary stability, it is a meaningless concept to the designer and the crew. The same is true of sail boats, catamarans, fishing boats, etc. Why would an industry attempt to define an undetectable, meaningless phenomena with no commercial application? It is only kayakers that perceive it, and they are unique. And since it appears to be largely a perceived phenomenon not apparently detectable on the stability curves, hence the difficulty in measuring it. It had not even occurred to me until Matt mentioned that it does not show up on the stability curves. One would think that in a kayak with good secondary stability, the curves would get steeper toward the top, and ones with low secondary stability would have more rounded, flatter stability curves. But this is not the case so it must largely be based on perception of the kayaker. Following the thread I was thinking back of all of the other types of water craft and vessels I have been in (or piloted), from my limited experience, this notion and terminology does not even exist. Even on something as sensitive to body movement and weight shifting as a surf board, there is no concept of secondary stability. Curious. Must be because it is irrelevant to most water craft. It looks like if there is some measurable difference in secondary stability in hull designs it is up to the kayaking community (designers, manufactures, etc.) to figure out how to define and measure it. Apparently no one else is interested or even cares. You may even have to measure the kayaker's skill and coordination, and factor that into the physical parameters of the hull. Peter *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Peter wrote: , > > It might be that Navel Architecture does not consider and define "secondary > stability", as John points out, because it is not relevant to the vast > majority of vessels. Only in kayaks and perhaps smaller canoes can one > even perceive such a phenomena since you more or less wear the kayak and > control it by twists and shifts of your body. In an ocean liner or > freighter no one can feel secondary stability, it is a meaningless concept > to the designer and the crew. The same is true of sail boats, catamarans, > fishing boats, etc. First, I referred to the use of the term "secondary stability" and pointed out that naval archirtects refer to the phenomenon as "overall stability". Oveall stabilty applies to all boats. > > Why would an industry attempt to define an undetectable, meaningless > phenomena with no commercial application? It is only kayakers that > perceive it, and they are unique. And since it appears to be largely a > perceived phenomenon not apparently detectable on the stability curves, > hence the difficulty in measuring it. It is neither undectable or meaningless and does have a commecial application. > > It had not even occurred to me until Matt mentioned that it does not show > up on the stability curves. It does show up in the stabilty curves if you know what to look for. >One would think that in a kayak with good > secondary stability, the curves would get steeper toward the top, and ones > with low secondary stability would have more rounded, flatter stability > curves. But this is not the case so it must largely be based on perception > of the kayaker. Tell me what you perceive if not the forces acting on the boat. (SNIP) > It looks like if there is some measurable difference in secondary stability > in hull designs it is up to the kayaking community (designers, > manufactures, etc.) to figure out how to define and measure it. Apparently > no one else is interested or even cares. You may even have to measure the > kayaker's skill and coordination, and factor that into the physical > parameters of the hull. People do care, C.J. Marchaj wrote an entire book on it. The IMO has done extensive studies on it. Cheers, John Winters *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
<lots of snipping and sequence reordering follow> John wrote: >>>Clearly the less one needs to do to keep the boat upright the more stable it seems. So, if one righting moment curve is higher after the maximum than another (shallower slope) then the paddler will perceive it as having more stability. Using Matt's arm wrestling analogy one could say that it is a bit like the opponent slowly reducing his effort rather than relaxing completely.<<<< This seems to get to our major point of contention. John, have you read John Dawson's piece on what the stability curves shown in the Spring 1987 edition of Sea Kayaker? I'd love to quote it here but it is copyrighted material so I will point to the location where it can be found on the web www.marinerkayaks.com (in the reviews section at the end of the Mariner XL review). John Dawson reported to me personally that they had to measure the backside of the curves from the capsize point back up to the point of maximum stability because (going the other direction) once the kayak was angled past that point the stiffness becomes negative and any motion towards leaning the kayak further (anywhere on the backside of the curve) resulted in an immediate full capsize of the kayak as the righting moment was further reduced the more the kayak was tilted and they were unable to release the pressure fast enough to prevent the capsize. So, what was to stop it from continuing to tilt further against a continually reducing righting moment? Sure, if you can arrest the fall with a paddle brace you may be able to hold a tenuous balance on the "backside" of the curve but you had better be ready to brace immediately because the kayak's stability won't help much here (like the still positive "static" righting moment makes it look like it should). Perhaps another analogy will be revealing. Well on second though perhaps it isn't totally apt and might just be confusing. Heck I worked on it long enough I hate to just throw it away so I'll make the those poor readers who haven't skipped right by this discussion (that maybe should be taken completely back channel) already and are still curious enough suffer through it too see if they think the analogy is somewhat comparable. Imagine we make two ramps in the shape of a stability curve to roll a ball bearing up and over. The front side of the curves are identical but one then drops straight down to zero at its peak and the other falls away like most static stability curves do. Question: Which ball will reach the (ground) zero point on the back side the quickest (if you were to roll it over both ramps equally hard and with plenty of momentum to easily make it over the hump)? I don't believe the path (through space) the two balls would take would be any different with these two ramps. Both balls would be in free fall the whole way down, one would just have gotten further away from its ramp because its ramp dropped away more suddenly. You might not notice the other was not quite touching its ramp on the backside. Sort of like an orbiting satellite continuing to fall past the earth due to its speed. Of course if you could get the force just right so the ball barely clears the peak the backside ramp would slow the fall a bit. Leaning your body will also shift the maximum point of the curve (but the equal and opposite reaction, if that were done too late, (that would further tilt the kayak) also might push the system into the ......"wetside" of the stability curve. John wrote: >>>I don't have any data to support "meaningless" and would suggest that if peope can sense the stability of the boat then it probably exceeds "meaningless". What do they sense if not the boat?<<<< That's my point, how many of us can sense the stability of the backside once our momentum has put us there and into the virtual freefall we call a capsize. John wrote: >>>>>That is, boat righting arm plus weight shift plus paddle forces. The greater the righting moment contributed by the boat after the maximum the less on needs of the other two to right the boat.<<<< While I can't disagree with anything you say here it is essentially irrelevant because that little righting component is so small compared with the righting moment that you can generate with your paddle blade that it would be inconsequential. In other words, it won't make the difference (whether you capsize or not) once in a thousand times. John Winters wrote earlier: <SNIP> >>>>Maybe I should help clear this up. The area under the curve does not constitute the totality of "overall stability". As I mentioned in an earlier post overall stability includes the area under the curve, the slopes of the curve, the range of stability and the location of maximum righting force or moment. All combine to provide what we sense as overall stability or secondary stability. Naval architects do not have a single measure of overall stability but utilize all factors.<<< As best as I can figure this out then "Overall stability" includes initial stability ("the slopes of the curve") and secondary stability (and apparently everything else about a hull's stability). Since it includes initial stability I don't see how it can also be equated with secondary stability unless secondary stability also includes initial stability. I have been unable to find a text at hand that includes this term so I am relying on the definition of overall stability John gave. This seems to be a very vague definition that essentially includes everything (and I was hoping to define out the various parts of "Stability" and understand how they differ from the other parts). Can somebody find a textbook quote for "overall stability". I assumed it was a term used to refer to the total energy required to capsize a static hull which I believe is a number that can be determined by the area under the curve. Would that area under the curve be called "total stability" or is there some other term that refers to the total energy expended to cause a capsize? Searching with Google I found what appears to be a US military website (thus not copyrighted) at http://www.fas.org/man/dod-101/navy/docs/swos/dca/index.html that says this: "FUNDAMENTALS OF STABILITY Stability is the tendency of a vessel to rotate one way or the other when forcibly inclined. Stability can be broken down into several categories, each of which are alternatively emphasized in designing and operating Navy and Coast Guard ships. STABILITY INITIAL STABILITY - The stability of a ship in the range from 0° to 7°/10° of inclination. OVERALL STABILITY - A general measure of a ship's ability to resist capsizing in a given condition of loading. DYNAMIC STABILITY - The work done in heeling a ship to a given angle of heel." It does say "overall stability" is a measure so it must somehow be quantifiable. Area under the curve? John seems to say it is much more than that but also includes that. Anybody know how it is measured? Well, that's certainly not how I've been using the term "dynamic stability". I've been using it more as a component of "Seakindliness" in rapidly changing (rough) wave slopes, wave angles, wave peaks and troughs. Maybe I'll have to make up my own word;-) Any suggestions. Maybe "Lateral Seakindliness" (as opposed to "Pitch Seakindliness" and Yaw Seakindliness") which all blend together into, you guessed it, "OVERALL SEAKINDLINESS".:-) Further on in the lesson on stability the text describes what info can be gotten from a Static Stability Graph: "Much information can be obtained from this curve, including: Range of Stability: This ship will generate Righting Arms when inclined from 0o to approximately 74o. (This curve usually assumes that the entire superstructure is watertight.) Maximum Righting Arm: The largest separation between the forces of buoyancy and gravity. This is where the ship exerts the most energy to right itself. Angle of Maximum Righting Arm: The angle of inclination where the maximum Righting Arm occurs. Danger Angle: One half the angle of the maximum Righting Arm. This "Danger Angle" sure sounds interesting I wonder why it is defined as 1/2 the angle of the maximum righting arm. Anybody out there understand "Danger Angle"? I couldn't find much on Google. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Matt wrote: >Imagine we make two ramps in the shape of a stability curve to roll a ball bearing up and over. The front side of the curves are identical but one then drops straight down to zero at its peak and the other falls away like most static stability curves do. Question: Which ball will reach the (ground) zero point on the back side the quickest (if you were to roll it over both ramps equally hard and with plenty of momentum to easily make it over the hump)? If the velocity of the ball were sufficiently high so that the ball would lose contact with the curve after reaching the maximu then you are absolutely right. Are you saying that all capsizes result from this kind of rotational velocity? (SNIP) John wrote: >>>I don't have any data to support "meaningless" and would suggest that if peope can sense the stability of the boat then it probably exceeds "meaningless". What do they sense if not the boat?<<<< >That's my point, how many of us can sense the stability of the backside once our momentum has put us there and into the virtual freefall we call a capsize. Are you saying that if you can't sense the righting force it doesn't exist? John wrote: >>>>>That is, boat righting arm plus weight shift plus paddle forces. The greater the righting moment contributed by the boat after the maximum the less on needs of the other two to right the boat.<<<< >While I can't disagree with anything you say here it is essentially irrelevant because that little righting component is so small compared with the righting moment that you can generate with your paddle blade that it would be inconsequential. In other words, it won't make the difference (whether you capsize or not) once in a thousand times. What science do you have to support "irrelevant"? Thanks to Matt for all the information he dug up that supports my arguments by providing the various aspects of stability and how one quantifies them. Unfortunately none of them relate to a measure of how one "feels" about stability. Cheers, John Winters *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
At 11:37 PM -0800 11/16/00, Matt Broze wrote: > >Imagine we make two ramps in the shape of a stability curve to roll a ball >bearing up and over. The front side of the curves are identical but one then >drops straight down to zero at its peak and the other falls away like most >static stability curves do. Question: Which ball will reach the (ground) >zero point on the back side the quickest (if you were to roll it over both >ramps equally hard and with plenty of momentum to easily make it over the >hump)? > >I don't believe the path (through space) the two balls would take would be >any different with these two ramps. Both balls would be in free fall the >whole way down, one would just have gotten further away from its ramp >because its ramp dropped away more suddenly. You might not notice the other >was not quite touching its ramp on the backside. Sort of like an orbiting >satellite continuing to fall past the earth due to its speed. Of course if >you could get the force just right so the ball barely clears the peak the >backside ramp would slow the fall a bit. I don't see how the analogy of a ball flying through the air is a good analogy for stability. A ball is free to fly so the shape of the ramp may not effect it's travel, but a boat must stick to it's curve. There seems to be a growing consensus that because we are having difficulty defining "secondary" stability that it must be meaningless and if it means anything, it is the same as "overall" stability. I think many kayakers would dispute that. They can feel a secondary stability and know a boat that has it. Take an extreme example of a boat with a distinct "V" bottom and low flat deck (almost diamond shaped in section). This boat could have low "initial" but high "secondary". With the low deck, it may also be quite easy to turn completely over in which case the "overall" stability may not be great. In this case there is something between "initial" and "overall" which is significant. This is what people call "secondary". Instead of throwing the baby out with the bath water, why don't we try to define what "secondary" is and how it differs from "overall". If the stability curve crosses zero at 60 degrees, a paddler sitting bolt upright and doing nothing to recover at 59 degrees of lean will return to the upright position. The recovery might be slow, but if no other forces are applied, recovery is inevitable. This does not seem to me to be related to "secondary", but must somehow belong in the "overall" camp. Previously John has suggested the area under the curve as being indicative of overall stability. The area indicates the amount of work or energy required to capsize the boat until the point of no return, with an inert passenger. An inactive paddler is not realistic, but people are hard to predict, so we are stuck with it. By using area a boat with a high narrow stability curve and one with a wide flat curve are both shown to be hard to tip upside down. This seems to be what we want to know about "overall" stability. Secondary is a little harder to pin down. I think what people call "secondary" is the feel that it is taking progressively more effort to effect a change in the lean. Some boats, you lean a little bit, the boat responds, you lean a little be more, it responds about the same, more lean, similar response. Some boats, you lean, it responds a bit, lean a little more and it responds more than before, more lean and an accelerated response. Other boats, you start leaning and the boat responds, you lean more, and the boat doesn't respond quite as much, more lean, even less response. These last boats tend to be characterized as having good secondary stability. The boat "stiffens" as it is leaned. This tendency can be seen in the stability curve by analyzing the slope of the curve. The rate of change of the stability indicates whether it is going to take progressively more effort to create a given change or progressively less. Mathematical types will look at the derivative of the stability curve. Some curves start out steep and bend continuously downward. Others start out relatively flat, then curve upwards before straightening out and starting to bend down. These are the boats which "stiffen". The inflection point, where the curve changes from upwards tending to downwards tending will probably tell us something about "secondary" stability. (for those mathematicians still following, the inflection point is the maximum of the derivative, or the zero crossing of the second derivative) The possible characteristics to look at for this form of "secondary" stability are: the slope of the curve at the inflection, the height of the curve at the inflection, the angle of lean at the inflection or the area of under the curve until the inflection point. After a little thought, I am going to say a boat with "good" secondary stability will be one where the angle of the inflection point is the highest. This will be the boat where you can lean the boat the most before the ability to recover starts to fall apart. Beyond the inflection point, less and less effort will be required to create the same effect on the boat until you reach the top of the stability curve where the slightest increase in effort will cause a capsize. I am certain, that a lot of people won't agree with this definition, but I think it does address some of the concerns. Nick -- Nick Schade Guillemot Kayaks 824 Thompson St, Suite I Glastonbury, CT 06033 (860) 659-8847 Schade_at_guillemot-kayaks.com http://www.guillemot-kayaks.com/ >>>>"It's not just Art, It's a Craft!"<<<< *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). 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Nick Schade wrote: [snip] > Secondary is a little harder to pin down. I think what people call > "secondary" is the feel that it is taking progressively more effort > to effect a change in the lean. Some boats, you lean a little bit, > the boat responds, you lean a little be more, it responds about the > same, more lean, similar response. Some boats, you lean, it responds > a bit, lean a little more and it responds more than before, more lean > and an accelerated response. Other boats, you start leaning and the > boat responds, you lean more, and the boat doesn't respond quite as > much, more lean, even less response. These last boats tend to be > characterized as having good secondary stability. The boat "stiffens" > as it is leaned. > > This tendency can be seen in the stability curve by analyzing the > slope of the curve. The rate of change of the stability indicates > whether it is going to take progressively more effort to create a > given change or progressively less. Mathematical types will look at > the derivative of the stability curve. > > Some curves start out steep and bend continuously downward. Others > start out relatively flat, then curve upwards before straightening > out and starting to bend down. These are the boats which "stiffen". > The inflection point, where the curve changes from upwards tending to > downwards tending will probably tell us something about "secondary" > stability. (for those mathematicians still following, the inflection > point is the maximum of the derivative, or the zero crossing of the > second derivative) > > The possible characteristics to look at for this form of "secondary" > stability are: the slope of the curve at the inflection, the height > of the curve at the inflection, the angle of lean at the inflection > or the area of under the curve until the inflection point. > > After a little thought, I am going to say a boat with "good" > secondary stability will be one where the angle of the inflection > point is the highest. This will be the boat where you can lean the > boat the most before the ability to recover starts to fall apart. > Beyond the inflection point, less and less effort will be required to > create the same effect on the boat until you reach the top of the > stability curve where the slightest increase in effort will cause a > capsize. > > I am certain, that a lot of people won't agree with this definition, > but I think it does address some of the concerns. Comment from the peanut gallery: keep it up, you three (four?). I'm learning stuff here. My (very small) two cents: Nick's definition is an easy to measure and quantify one, and seems to have a basis in physics. However, perhaps a shot of empiricism might be in order: 1. gather up half a dozen competent paddlers and half a dozen (varied) boats. (The paddlers have to be folks who regularly test the secondary stability of their boats, not placid paddlers like me.) 2. put them into each of the boats and ask them to "test" each one for its secondary stability. 3. have them tell an observer at which angle they begin to "feel" the secondary stability, and have them rank each boat for its "secondary stability." Then compare their results with Nick's criteria to see if experience (with all the limitations Winters has delineated) jives with Nick's stab at a definition. I think we need data to test Nick's suggestion, though the debate has been interesting. We might also find that the data show us nature has whacked us upside our heads with the "real" answer while we were trying to test the one we thought was correct. -- Dave Kruger Astoria, OR *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Nick wrote; (SNIP) > > There seems to be a growing consensus that because we are having > difficulty defining "secondary" stability that it must be meaningless > and if it means anything, it is the same as "overall" stability. I hope not. :-0 I may have failed to make myself clear but I thought I said that the term "secondary stability" seemed to be a canoe and kayak word that corresponded to what naval architects call "overall stability". I hope no one got the idea that I thought it meaningless. >They can feel a secondary > stability and know a boat that has it. Take an extreme example of a > boat with a distinct "V" bottom and low flat deck (almost diamond > shaped in section). This boat could have low "initial" but high > "secondary". With the low deck, it may also be quite easy to turn > completely over in which case the "overall" stability may not be > great. In this case there is something between "initial" and > "overall" which is significant. This is what people call "secondary". Overall stability as I understand it does not refer to any specific point but to stability as a whole. This is why one has to look at the slopes, area under the curve and range of stability to get a feel for how the curves relate to what we feel. Imagine a boat that had a concave stability curve that steeply rose to a maximum and then fell as steeply to the limit of its range. Such a boat would probably have a strange and unstable feel at all but a couple of degrees of heel and yet it would have a high maximum and a high range. Now imagine a boat with a lot of area under the curve but one that goes up nearly vertically at say 5 degrees and drops quickly at 10 degrees. Lots of area maybe but low overall stability. Now imagine a boat with a range of stability 40 degrees with a maximum at 40 degrees but only 1 pound of righting moment. Once again it has two of the conditions for "good" overall stability but not the third. Defining stability by a "point" or single factor only seems to work with initial stability . > If the stability curve crosses zero at 60 degrees, a paddler sitting > bolt upright and doing nothing to recover at 59 degrees of lean will > return to the upright position. The recovery might be slow, but if no > other forces are applied, recovery is inevitable. This does not seem > to me to be related to "secondary", but must somehow belong in the > "overall" camp. Previously John has suggested the area under the > curve as being indicative of overall stability. I suggested it as part of overall stability (see above). I hope no one got the idea that I said it formed the only part. > the amount of work or energy required to capsize the boat until the > point of no return, with an inert passenger. An inactive paddler is > not realistic, but people are hard to predict, so we are stuck with > it. By using area a boat with a high narrow stability curve and one > with a wide flat curve are both shown to be hard to tip upside down. > This seems to be what we want to know about "overall" stability. (SNIP) > The possible characteristics to look at for this form of "secondary" > stability are: the slope of the curve at the inflection, the height > of the curve at the inflection, the angle of lean at the inflection > or the area of under the curve until the inflection point. YEA TEAM! I would like to say that my arguments persuaded Nick but I know better. He certainly phrased it better than I. > > After a little thought, I am going to say a boat with "good" > secondary stability will be one where the angle of the inflection > point is the highest. This will be the boat where you can lean the > boat the most before the ability to recover starts to fall apart. > Beyond the inflection point, less and less effort will be required to > create the same effect on the boat until you reach the top of the > stability curve where the slightest increase in effort will cause a > capsize. > I would like to add to this. Once past the maximum the shallower the slope the lower the effort required to restore positive righting. For example, suppose a boat had 20 lbs maximum righting moment at 20 degrees of heel as shown by the static curve. At 21 pounds of heeling moment the boat begins to capsize. But if the paddler applies some righting force either with a brace or by shifting weight she can restore positive righting moment. If the curve just dropped vertically (not likely but what the heck) she would have to apply 21 pounds (or more) of righting force instantaneously to effect righting. If the curve continued on at such a slope that at 25 degrees of heel the static curve showed 10 pounds of righting moment then she would only have to supply 11 pounds of righting force at 25 degrees of heel to prevent a capsize. The more the boat does the less the paddler has to do. Now, the paddler may not take time to "measure" the forces and probably overreacts a bit but in any case if she has derived more help in keeping the boat upright she will perceive the boat as having more stability at that point. (Choose the name you like :-0 ) Passing the peak of the static curve does not mean inevitable capsize and the boat's contribution after that point makes it easier to avoid capsize. In any case, defining what a person feels seems a tough one since few of us feel the same thing in the same way. The stability curve and its magnitudes provide a visual way to relate our perceptions to quantifiable forces. Cheers, JW *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Dave Kruger wrote: > > I think we need data to test Nick's suggestion, though the debate has been > interesting. We might also find that the data show us nature has whacked us > upside our heads with the "real" answer while we were trying to test the one we > thought was correct. As I read the very interesting dialogue in which chines are taking it on the chin, I recall a story supposedly true: When Thomas Edison and his laboratory associates were working on the light bulb they ran across a problem: how to measure the volume of the light bulb area which would be filled with gases. His associates went into elaborate caliberations of the cylinder portion and the globe portion, etc. to figure out the estimated volume. Edison, busily working away at some other aspect of the project, looked over and saw his colleagues mathematical machinations struggle. He went over, grabbed the light bulb, took it to a lab faucet, filled it with water and then poured the water into a measuring beaker. "Gentlemen, here is your volume!" While the story is not exactly applicable to the current debate, it does say something about how a more direct approach can prove helpful. best, ralph -- ----------------------------------------------------------------------- Ralph Diaz . . . Folding Kayaker newsletter PO Box 0754, New York, NY 10024 Tel: 212-724-5069; E-mail: rdiaz_at_ix.netcom.com "Where's your sea kayak?"----"It's in the bag." ----------------------------------------------------------------------- *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
And I would imagine (note: strictly conjecture) that differing body types, length of torso above the cockpit, torso weight distribution, and, of course, head mass would contribute to widely differing perceptions as to the amount of heel a kayak is capable of before capsize. Could be risky kayaking with a swelled head... > In any case, defining what a person feels seems a tough one since few of us > feel the same thing in the same way. The stability curve and its magnitudes > provide a visual way to relate our perceptions to quantifiable forces. > > Cheers, > > JW -- : : Gabriel L Romeu : http://studiofurniture.com furniture from the workshop : http://members.xoom.com/gabrielR life as a tourist, daily journal : http://studiofurniture.com/paint paintings, photographs, etchings, objects *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Gabriel wrote; > And I would imagine (note: strictly conjecture) that differing body > types, length of torso above the cockpit, torso weight distribution, > and, of course, head mass would contribute to widely differing > perceptions as to the amount of heel a kayak is capable of before > capsize. > > Could be risky kayaking with a swelled head... > You bet, although if the head swells enough it serves as a righting device sort of like one of those Backups or maybe a cranial sp*s*n. The differences in people make it difficult to apply individual perceptions across the range of paddlers. John Winters Waveform Plastics Technologies Ltd. 15 Ena Ave. South River, Ontario P0A 1X0 *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Ralph wrote: > > When Thomas Edison and his laboratory associates were working on the > light bulb they ran across a problem: how to measure the volume of the > light bulb area which would be filled with gases. His associates went > into elaborate caliberations of the cylinder portion and the globe > portion, etc. to figure out the estimated volume. Edison, busily > working away at some other aspect of the project, looked over and saw > his colleagues mathematical machinations struggle. He went over, > grabbed the light bulb, took it to a lab faucet, filled it with water > and then poured the water into a measuring beaker. "Gentlemen, here is > your volume!" > > While the story is not exactly applicable to the current debate, it does > say something about how a more direct approach can prove helpful. So, if we fill a paddle with water we will know how stable he is? :-) Cheers, John Winters Waveform Plastics Technologies Ltd. 15 Ena Ave. South River, Ontario P0A 1X0 *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
On Thu 16 Nov 2000, Matt Broze wrote: > Imagine we make two ramps in the shape of a stability curve to roll a ball > bearing up and over. The front side of the curves are identical but one then > drops straight down to zero at its peak and the other falls away like most > static stability curves do. Question: Which ball will reach the (ground) > zero point on the back side the quickest (if you were to roll it over both > ramps equally hard and with plenty of momentum to easily make it over the > hump)? > > I don't believe the path (through space) the two balls would take would be > any different with these two ramps. Let's imagine me running down the stairs of a twelve story building and somebody else simply stepping of the edge from the roof. Your right. The path would not be that different. But what's your point? > That's my point, how many of us can sense the stability of the backside once > our momentum has put us there and into the virtual freefall we call a > capsize. Let's say I take a tippy boat and lean my torso out close to the going over pt and snap my head and shoulders to create a capsize, and then catch it with a high brace. Now I do the same with a very stable boat. Which is more likely to cause a shoulder injury? I'm guessing the more stable boat would be more likely to cause an injury because of the hull righting force being all used up on the front side of the curve. I would have to add that while the discussion on this thread (at least to my mind) tends to indicate that tippier boats would have less violent and more frequent instability events it's impossible to say that shoulder injury would be more likely as a result of the force or the frequency of events (ie I am not saying stable boats cause injuries). This would depend on the paddler and the waters paddled. I probably should have left injury out of the discussion, but thought it might serve to add meaning to the stability forces. There are no meaningless or insignificant stability forces, there are only trade-offs. I could be wrong about all this as I am not a boat designer. I do have an engineering degree so I feel qualified to discuss design criterion, but I'm not real certain about my theories right now as I am new to the discussion of boat design. Oh, and I didn't mean to be rude about the jumping off a bld thing... I just thought that was a humorous way of pointing out that every little bit of supportive resistance is important. -- Mike McNally mmcnally3_at_prodigy.net *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
Mike wrote: (SNIP) > > So if I'm right about this the chine discussion has helped to identify some > of the strengths of the "tippy boat" for me, but I'm still at quite a loss for > understanding why you would want a hard chined boat. It has been said that > the hard chines do a better job of resisting skid. I would add that for this > skid resistance there is a price paid in reduced stability. I don't know that the question is "to chine" or "not to chine" but whether the boat does what you want it to do regardless of shape. Cheers, John Winters Waveform Plastics Technologies Ltd. 15 Ena Ave. South River, Ontario P0A 1X0 *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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