I am perplexed by the variety of sea kayaks and the use of rocker. Once you decide on total load and your level of skill (stability), it seems to me that the intended use dictates the rest of the design. Yet every manufacturer seems to offer several boats with variation in rocker being one of the principal differences. What am I missing? Assumptions: (1) The boat should be usable in rough conditions without its rudder. (2) Leaning the boat a little causes it to turn away from the lean because the low side is longer on the water than the high side, causing lift aft. Thus lean can be used to steer in open water. (3) Leaning the boat a lot increases rocker and shortens the waterline, making the boat easier to turn with the paddle, but decreases tracking ability. (4) Increasing base rocker makes the boat more maneuverable with the paddle, but decreases tracking ability. Based on the foregoing, it seems to me that a sea kayak should have little if any base rocker; otherwise it will be difficult to paddle in windy conditions without a rudder. It should also be designed so that at high lean, it has abundant rocker and a shorter waterline. This will permit maneuvering in tight quarters. The rudder is only used to help a bit in windy conditions and when surfing. If the foregoing is true, why would anyone choose say a Seawards Vision over a Seawards Navigator for sea kayaking? These boats are identical except for rocker. Similarly, why do many people like the Looksha IV? Without its rudder, it is hard to paddle in strong wind. Ken Cooperstein *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
> Based on the foregoing, it seems to me that a sea kayak should have > little if any base rocker I am not a designer, but we have a couple of excellent ones on this list. Maybe we will hear from them. I do have a comment as a paddler. I have a 17 foot cedar strip Guillemot, designed by Nick Schade. It does not track as straight as some other boats, but since I do most of my paddling in areas with lots of small bays and island shores to explore, as well as currents, I really like its turning ability. I have no problems keeping it going straight when I want to go that way, but it turns so easily and even more when leaned, that it is a delight to use in my home conditions. I sometimes paddle with a friend in a Seda Glider,which he likes for racing. I can be in and out of a small bay in the time that it takes him to turn in. He likes his ability to track straight, I like my ability to turn and paddle straight both. I have another kayak that tracks as if it was on rails (except in cross winds), but I much prefer the Guillemot. Not to start anything again, but I did not put a rudder on the Guillemot when I made it and don't feel that it needs it. On the other hand, a friend's daughter tried it for her first experience in a kayak, and spent the first 10 minutes paddling in circles. If I was going on a long crossing trip, or was racing, I might want something that tracks very straight, but I don't feel that that is always the most desireable feature. There is a trade off in every design. John *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
|If the foregoing is true, why would anyone choose say a Seawards Vision |over a Seawards Navigator for sea kayaking? These boats are identical |except for rocker. Similarly, why do many people like the Looksha IV? |Without its rudder, it is hard to paddle in strong wind. What is "strong wind?" I have paddled my Looksha IV in 30+mph winds. Not that I wanted to but that is what happened. I think that is a strong wind. The normal wind I paddle in is 10-15 mph. I don't have a problem paddling the Looksha in wind at all. What is a problem are following or stern quartering seas. Then a rudder helps control broaching. At first I thought I was going to get an Arluk III. But after paddling the Arluk, Looksha and a bunch of other boats at a symposium, I got the IV. Its ability to turn is outstanding and I have used it in very tight turning channels in marshes and rivers. Most of my paddling is done on large local lakes where wind is an issue. If the wind is effecting the course I want, I can easily lean the Looksha and away we go. Shortening up on the paddle so that your paddle stroke is shorter on the upwind side of the boat also helps. After I had the Looksha for a few months I had the opportunity to paddle an Arluk III again in 5-10 mph winds. I really disliked the Arluk because I was so used to paddling the Looksha that keeping on course was so much easier in the IV than the III. Just a movement of my fanny would keep the course I wanted. I very seldom use my rudder. A thread running a few weeks ago was talking about tracking, loading of the boat, etc. A new person to the thread said something that reminded me to try to put more wieght in the forward part of the yak. I finally remembered that I had a dive belt and I'm going to start using it to see what effect it has on putting some weight forward. Hope this helps... Dan McCarty *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Ken; Most paddlers don't have any idea about what their skill level is. Also it is the exceptional paddler who learns how to handle their boat using varying strokes, edging, ruddering, weight shifting etc. Add to this the fact that loads tend to vary depending on equipment and days on the water etc and it is not surprising that there are many different hull shapes and varying rocker on different boats. I suspect that first boat purchases have more to do with the emotional experience of how the day went when a particular boat was tried or boat easthetics than anything else. Additionally, my experience is that boats which track very straight and have little or no rocker are still a pain in the neck to turn even when put on edge. Having no rocker can also be a real hassle in following seas. John Winskill ----- Original Message ----- From: Kenneth Cooperstein <cprstnc1_at_optonline.net> To: paddlewise, paddlewise <PaddleWise_at_lists.intelenet.net> Sent: Wednesday, September 29, 1999 6:34 AM Subject: [Paddlewise] Rocker: too many sea kayaks > I am perplexed by the variety of sea kayaks and the use of rocker. Once > you decide on total load and your level of skill (stability), it seems > to me that the intended use dictates the rest of the design. Yet every > manufacturer seems to offer several boats with variation in rocker being > one of the principal differences. What am I missing? > > Assumptions: > > (1) The boat should be usable in rough conditions without its rudder. > > (2) Leaning the boat a little causes it to turn away from the lean > because the low side is longer on the water than the high side, causing > lift aft. Thus lean can be used to steer in open water. > > (3) Leaning the boat a lot increases rocker and shortens the waterline, > making the boat easier to turn with the paddle, but decreases tracking > ability. > > (4) Increasing base rocker makes the boat more maneuverable with the > paddle, but decreases tracking ability. > > Based on the foregoing, it seems to me that a sea kayak should have > little if any base rocker; otherwise it will be difficult to paddle in > windy conditions without a rudder. It should also be designed so that > at high lean, it has abundant rocker and a shorter waterline. This will > permit maneuvering in tight quarters. The rudder is only used to help a > bit in windy conditions and when surfing. > > If the foregoing is true, why would anyone choose say a Seawards Vision > over a Seawards Navigator for sea kayaking? These boats are identical > except for rocker. Similarly, why do many people like the Looksha IV? > Without its rudder, it is hard to paddle in strong wind. > > Ken Cooperstein > > > > *************************************************************************** > PaddleWise Paddling Mailing List > Submissions: paddlewise_at_lists.intelenet.net > Subscriptions: paddlewise-request_at_lists.intelenet.net > Website: http://www.paddlewise.net/ > *************************************************************************** *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
On Wed, 29 Sep 1999, Kenneth Cooperstein wrote: [snip] > Assumptions: > [snip] > (2) Leaning the boat a little causes it to turn away from the lean > because the low side is longer on the water than the high side, causing > lift aft. Thus lean can be used to steer in open water. leaning the boat will not cause the boat to turn. this is one of the things we stress teaching canoeing. if the boat is going in a straight line, and you lean left, you keep going in a straight line. if the boat is turning left, and you lean left, you turn a bit faster. if the boat is turning left, and you lean right, you turn left FAST, this is called a "jam turn" [snip] > If the foregoing is true, why would anyone choose say a Seawards Vision > over a Seawards Navigator for sea kayaking? These boats are identical > except for rocker. Similarly, why do many people like the Looksha IV? > Without its rudder, it is hard to paddle in strong wind. > > Ken Cooperstein personal preference & skill level. a toyota camry & honda accord are nearly identical, and both sell a buttload of them... mark -- #------canoeist[at]netbox[dot]com----http://www.diac.com/~zen/mark ---- # mark zen o, o__ o_/| o_. po box 474 </ [\/ [_| [_\ ft. lupton, co 80621-0474 (`-/-------/----') (`----|-------\-') #~~~~~~~~~~~~~~~~~~~~~~~~~~~_at_~~~~~~~_at_~~~~~~~~~~~~~~~~~~~_at_~~~~~~~~_at_~~~~~ http://www.diac.com/~zen/paddler [index to club websites i administer] Rocky Mtn Sea Kayak Club, Colorado River Flows, Poudre Paddlers The Colorado Paddlers' Resource, Rocky Mtn Canoe Club Trip Page -- Fortune: One kind word can warm three winter months. --Japanese Proverb *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Mark Zen wrote: > On Wed, 29 Sep 1999, Kenneth Cooperstein wrote: > [snip] > > Assumptions: > > > [snip] > > (2) Leaning the boat a little causes it to turn away from the lean > > because the low side is longer on the water than the high side, causing > > lift aft. Thus lean can be used to steer in open water. > > leaning the boat will not cause the boat to turn. I beg to differ. This is one of the tests I conduct on a kayak when I paddle it. I get up to speed, stop paddling and drift a bit. Then, _without_ a sweep stroke, I lean the kayak. Good ones turn opposite the lean. Mike *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
At 20:09 9/29/99 -0400, Michael Daly wrote: >Mark Zen wrote: >> On Wed, 29 Sep 1999, Kenneth Cooperstein wrote: >> [snip] >> > Assumptions: >> > >> [snip] >> > (2) Leaning the boat a little causes it to turn away from the lean >> > because the low side is longer on the water than the high side, causing >> > lift aft. Thus lean can be used to steer in open water. >> >> leaning the boat will not cause the boat to turn. > >I beg to differ. This is one of the tests I conduct on a kayak when I paddle >it. I get up to speed, stop paddling and drift a bit. Then, _without_ a sweep >stroke, I lean the kayak. Good ones turn opposite the lean. > >Mike mike, you snipped: ==== if the boat is going in a straight line, and you lean left, you keep going in a straight line. if the boat is turning left, and you lean left, you turn a bit faster. if the boat is turning left, and you lean right, you turn left FAST, this is called a "jam turn" ==== i am fairly willing to bet the boat has started a turn before you lean, and you were performing a jam turn... to become certified as a _canoe_ instructor, we had to demonstrate this principle to the instructor trainer... from what i know of hull shapes, the same _should_ be true of sea kayaks as well... whitewater kayaks probably fit that catagory, but i'm sure some of the play boats do strange things... mark #------canoeist[at]netbox[dot]com-------------------------------------- mark zen o, o__ o_/| o_. po box 474 </ [\/ [\_| [\_\ ft. lupton, co 80621-0474 (`-/-------/----') (`----|-------\-') #~~~~~~~~~~~~~~~~~~~~~~~~~~~_at_~~~~~~~_at_~~~~~~~~~~~~~~~~~~~_at_~~~~~~~~_at_~~~~~ http://www.diac.com/~zen/paddler [index of Paddling websites I manage] Rocky Mtn Sea Kayak Club, Colorado River Flows, Poudre Paddlers The Colorado Paddlers' Resource, Rocky Mtn Canoe Club Trip Page -- Computers are useless. They can only give you answers. --Pablo Picasso *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Mark Zen wrote: > At 20:09 9/29/99 -0400, Michael Daly wrote: > [...] > i am fairly willing to bet the boat has started a turn before you lean, > and you were performing a jam turn... No, I make sure I'm going straight- I check a spot on the horizon to ensure that I have no turning moments active. As well, if what you say is true, then I shouldn't be able to do a slalom just by leaning, but I can do that with some boats as well. The Swift North Sea (J. Winters design) does this nicely. Lean one way, then the other and the boat will turn one way, then the other - all without paddle strokes. In fact, when I took my first kayak lesson, the instructor told me to work on leaning the kayak and keeping the kayak _straight_ as an exercise in boat control and balance in heeling. What's true of a canoe isn't necessarily true of sea kayaks. I've solo paddled canoes often enough to know that they don't automatically turn on edge. Note as well, in WW kayaks, you lean the opposite way that you do in sea kayaks to turn. Mike *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
-----Original Message----- From: Kenneth Cooperstein <cprstnc1_at_optonline.net> >I am perplexed by the variety of sea kayaks and the use of rocker. Once >you decide on total load and your level of skill (stability), it seems >to me that the intended use dictates the rest of the design. Yet every >manufacturer seems to offer several boats with variation in rocker being >one of the principal differences. What am I missing? Lots. A little knowledge can be a dangerous thing. As I have said before, I'd suggest as a buyer you judge a kayak by how it feels to you under a variety of conditions when you paddle it and quit trying to analyze what you think it should do based on a little information (or misinformation) you have gathered. > >Assumptions: > >(1) The boat should be usable in rough conditions without its rudder. I agree > >(2) Leaning the boat a little causes it to turn away from the lean >because the low side is longer on the water than the high side, causing >lift aft. Thus lean can be used to steer in open water. No, this would cause lift sideways unless the hull is also asymetrical (then the widest part will lift more). If the maximum width is behind center you will be right then. > >(3) Leaning the boat a lot increases rocker and shortens the waterline, >making the boat easier to turn with the paddle, but decreases tracking >ability. Yes and it also angles the stern keel allowing it to slide easier. > >(4) Increasing base rocker makes the boat more maneuverable with the >paddle, but decreases tracking ability. Maybe if all other things are equal, but since they rarely are and so many other factors are involved here I wouldn't make this a general assumption. > >Based on the foregoing, it seems to me that a sea kayak should have >little if any base rocker; otherwise it will be difficult to paddle in >windy conditions without a rudder. You're way off base here. Much depends where the rocker is. Also a more manueverable kayak is often easier to keep on course because you can use that manueverability to more easily compensate for the kayaks less desireable tendencies. >It should also be designed so that >at high lean, it has abundant rocker and a shorter waterline. This will >permit maneuvering in tight quarters. Unfortunately you might not want a big wide kayak like this and even if you do it is now harder to lean it to take advantage of this ability. >The rudder is only used to help a >bit in windy conditions and when surfing. If it is needed at all then. > >If the foregoing is true, why would anyone choose say a Seawards Vision >over a Seawards Navigator for sea kayaking? These boats are identical >except for rocker. Yes that is the difference. The Navigator was critizied in its Sea Kayker review because it was so hard to turn, turning into strong winds was nearly impossible. The Vision was Seawards answer (but to my tastes it was an improvement but not nearly enough). >Similarly, why do many people like the Looksha IV? >Without its rudder, it is hard to paddle in strong wind. I'd guess they like its sporty manueverability. If by hard to handleyou mean its tendency to weathercock in sidewinds you can either choose to use the rudder then or learn the skills let you use that kayaks extra manueverability to help make the necessary corrections. A long list of weatherhelm compensating skills is in Manuals/Paddling Skills at www.marinerkayaks.com. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
-----Original Message----- From: Mark Zen <canoeist_at_netbox.com> To: paddlewise_at_lists.intelenet.net <paddlewise_at_lists.intelenet.net> Date: Wednesday, September 29, 1999 12:03 PM Subject: Re: [Paddlewise] Rocker: too many sea kayaks >On Wed, 29 Sep 1999, Kenneth Cooperstein wrote: >[snip] >> Assumptions: >> >[snip] >> (2) Leaning the boat a little causes it to turn away from the lean >> because the low side is longer on the water than the high side, causing >> lift aft. Thus lean can be used to steer in open water. > >leaning the boat will not cause the boat to turn. this is one of the >things we stress teaching canoeing. if the boat is going in a straight >line, and you lean left, you keep going in a straight line. if the boat is >turning left, and you lean left, you turn a bit faster. if the boat is >turning left, and you lean right, you turn left FAST, this is called a >"jam turn" >[snip] This is true for most standard "canoe" shapes, but not for radically asymmetrical or very hard chine shapes. For example Sea Kayaker's review of our Max said: "The Max tracked well for all of our reviewers, while still being very responsive to leaned turns. DL reported that he could "easily glide through an S [turn] with no paddle strokes at all." The full review is at http://www.marinerkayaks.com/mkhtml/MAXRVTXT.html. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
-----Original Message----- From: Mark Zen <canoeist_at_netbox.com> >At 20:09 9/29/99 -0400, Michael Daly wrote: >>Mark Zen wrote: >>> On Wed, 29 Sep 1999, Kenneth Cooperstein wrote: >>> [snip] >>> > Assumptions: >>> > >>> [snip] >>> > (2) Leaning the boat a little causes it to turn away from the lean >>> > because the low side is longer on the water than the high side, causing >>> > lift aft. Thus lean can be used to steer in open water. >>> >>> leaning the boat will not cause the boat to turn. >> >>I beg to differ. This is one of the tests I conduct on a kayak when I paddle >>it. I get up to speed, stop paddling and drift a bit. Then, _without_ a sweep >>stroke, I lean the kayak. Good ones turn opposite the lean. >> >>Mike > >mike, >you snipped: >==== >if the boat is going in a straight line, and you lean left, you keep going >in a straight line. if the boat is turning left, and you lean left, you turn >a bit faster. if the boat is turning left, and you lean right, you turn left FAST, >this is called a "jam turn" >==== >i am fairly willing to bet the boat has started a turn before you lean, >and you were performing a jam turn... >to become certified as a _canoe_ instructor, we had to demonstrate this >principle to the instructor trainer... Do you have this somewhere in writing. I'd like to add it to my "misinformation from the ACA" file but first I must see the original source to understand if they are operating from a limited perspective or you have broadened their meaning into area it was not meant to cover. Did they use any qualifiers? >from what i know of hull shapes, >the same _should_ be true of sea kayaks as well... whitewater kayaks probably >fit that catagory, but i'm sure some of the play boats do strange things... Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
-----Original Message----- From: Michael Daly <michaeldaly_at_home.com> >Mark Zen wrote: > >> On Wed, 29 Sep 1999, Kenneth Cooperstein wrote: >> [snip] >> > Assumptions: >> > >> [snip] >> > (2) Leaning the boat a little causes it to turn away from the lean >> > because the low side is longer on the water than the high side, causing >> > lift aft. Thus lean can be used to steer in open water. >> >> leaning the boat will not cause the boat to turn. > >I beg to differ. This is one of the tests I conduct on a kayak when I paddle >it. I get up to speed, stop paddling and drift a bit. Then, _without_ a sweep >stroke, I lean the kayak. Good ones turn opposite the lean. > >Mike Me too! I judge skis this way too. Some skis must be first be put into a turn to initiate a carved turn, but a really good pair only take a subtle edge change to do the job. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Putting weight forward will tend to aggravate the most common difficult handling situations. It may help some in headwinds but that is not a condition people generally have difficulty with. Be sure to try the dive belt in the stern though, it should reduce weatherhelm and broaching tendencies.. Matt Broze http://www.marinerkayaks.com -----Original Message----- From: dmccarty_at_us.ibm.com <dmccarty_at_us.ibm.com> >|If the foregoing is true, why would anyone choose say a Seawards Vision >|over a Seawards Navigator for sea kayaking? These boats are identical >|except for rocker. Similarly, why do many people like the Looksha IV? >|Without its rudder, it is hard to paddle in strong wind. > >What is "strong wind?" I have paddled my Looksha IV in 30+mph winds. Not that >I wanted to but that is what happened. I think that is a strong wind. The >normal wind I paddle in is 10-15 mph. > >I don't have a problem paddling the Looksha in wind at all. What is a problem >are following or stern quartering seas. Then a rudder helps control broaching. > >At first I thought I was going to get an Arluk III. But after paddling the >Arluk, Looksha and a bunch of other boats at a symposium, I got the IV. Its >ability to turn is outstanding and I have used it in very tight turning channels >in marshes and rivers. > >Most of my paddling is done on large local lakes where wind is an issue. If the >wind is effecting the course I want, I can easily lean the Looksha and away we >go. Shortening up on the paddle so that your paddle stroke is shorter on the >upwind side of the boat also helps. > >After I had the Looksha for a few months I had the opportunity to paddle an >Arluk III again in 5-10 mph winds. I really disliked the Arluk because I was so >used to paddling the Looksha that keeping on course was so much easier in the IV >than the III. Just a movement of my fanny would keep the course I wanted. > >I very seldom use my rudder. > >A thread running a few weeks ago was talking about tracking, loading of the >boat, etc. A new person to the thread said something that reminded me to try to >put more wieght in the forward part of the yak. I finally remembered that I had >a dive belt and I'm going to start using it to see what effect it has on putting >some weight forward. > > >Hope this helps... >Dan McCarty > > > > >*************************************************************************** >PaddleWise Paddling Mailing List >Submissions: paddlewise_at_lists.intelenet.net >Subscriptions: paddlewise-request_at_lists.intelenet.net >Website: http://www.paddlewise.net/ >*************************************************************************** *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
On Thu, 30 Sep 1999, Matt Broze wrote: > From: Mark Zen <canoeist_at_netbox.com> > >if the boat is going in a straight line, and you lean left, you keep going > >in a straight line. if the boat is turning left, and you lean left, you > turn > >a bit faster. if the boat is turning left, and you lean right, you turn > left FAST, > >this is called a "jam turn" > >==== > >i am fairly willing to bet the boat has started a turn before you lean, > >and you were performing a jam turn... > >to become certified as a _canoe_ instructor, we had to demonstrate this > >principle to the instructor trainer... > > Do you have this somewhere in writing. I'd like to add it to my > "misinformation from the ACA" file but first I must see the original source > to understand if they are operating from a limited perspective or you have > broadened their meaning into area it was not meant to cover. Did they use > any qualifiers? no, i was hoping to back this up with a reference page, since i am 100% tired of flame wars... but notice _i_ made the disclaimer below. the instructor trainer i was refering to was the head of the ACA's WW canoe instructors program, and is also a boat designer. i have witnessed this precise thing more times than i can count in a canoe, it is NOT mis information. _I_ applied the knowledge i have and wrote very distinctly SHOULD... it DOES apply to canoes. i don't profess to know much about sea kayaks. all my "big boat" experience was on an aircraft carrier, working as an aircrew survival equipment specialist... mark > >from what i know of hull shapes, > >the same _should_ be true of sea kayaks as well... whitewater kayaks > probably > >fit that catagory, but i'm sure some of the play boats do strange things... > > Matt Broze > http://www.marinerkayaks.com -- #------canoeist[at]netbox[dot]com----http://www.diac.com/~zen/mark ---- # mark zen o, o__ o_/| o_. po box 474 </ [\/ [_| [_\ ft. lupton, co 80621-0474 (`-/-------/----') (`----|-------\-') #~~~~~~~~~~~~~~~~~~~~~~~~~~~_at_~~~~~~~_at_~~~~~~~~~~~~~~~~~~~_at_~~~~~~~~_at_~~~~~ http://www.diac.com/~zen/paddler [index to club websites i administer] Rocky Mtn Sea Kayak Club, Colorado River Flows, Poudre Paddlers The Colorado Paddlers' Resource, Rocky Mtn Canoe Club Trip Page -- Fortune: One kind word can warm three winter months. --Japanese Proverb *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Probably that was Tom Foster, who came up with, and is enamored of, "Paddling the Inner Circle". It's in one of his books, and there have been some articles in recent years in Canoe & Kayak. I was unaware of his being a boat designer... If so, maybe it was Bob Foote you're referring to... >> Do you have this somewhere in writing. I'd like to add it to my >> "misinformation from the ACA" file but first I must see the original source >> to understand if they are operating from a limited perspective or you have >> broadened their meaning into area it was not meant to cover. Did they use >> any qualifiers? > > the >instructor trainer i was refering to was the head of the ACA's WW canoe >instructors program, and is also a boat designer. i have witnessed this >precise thing more times than i can count in a canoe, it is NOT mis >information.................. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
|Putting weight forward will tend to aggravate the most common difficult |handling situations. It may help some in headwinds but that is not a |condition people generally have difficulty with. Be sure to try the dive |belt in the stern though, it should reduce weatherhelm and broaching |tendencies.. Hmmm. I thought I already had enough weight in my stern! 8-) The reason I was thinking putting the dive belt forward was to balance the load in the kayak. Lately I've been carrying a heavy load of camera equipment in the stern. So I figured the belt might help up front. I guess I"ll find out. I just want to see if I can ease any tendency for the Looksha to turn into the wind. Thanks... Dan McCarty *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
>I am perplexed by the variety of sea kayaks and the use of rocker. Does get confusing especially since the sectional shape also influences how a boat turns (or doesn't turn). For example, "U" shaped sections can have less resistance to lateral motion than "V'd" sections. Attributing how a boat handles just to rocker probably simplifies things too much. A boat with "U" sections aft and a straight keel could have less controllability than a boat with some rocker and "V'd" sections aft. >you decide on total load and your level of skill (stability), it seems >to me that the intended use dictates the rest of the design. Yet every >manufacturer seems to offer several boats with variation in rocker being >one of the principal differences. What am I missing? People differ, paddling objectives differ, conditions differ and designers differ so I suppose it only reasonable that boats differ. >Assumptions: > >(1) The boat should be usable in rough conditions without its rudder. So long as you have an ARPEE it won't matter much. :-) I guess it would help to know what "useable" means and at what point "rough" becomes "who cares how well it handles I just hope it blows over soon". :-) >(2) Leaning the boat a little causes it to turn away from the lean >because the low side is longer on the water than the high side, causing >lift aft. Thus lean can be used to steer in open water. Not always or for all boats. Once a turn gets initiated lean can accelerate the turn in either direction. I don't think that "lift" occurs aft (At least not on the hull. Different matter with a rudder) . I think heel just reduces the lateral resistance aft. If lift did get generated it does not appear that it would act aft of the center of gravity given the forward motion of the boat. Some boats also trim down by the bow when heeled and that reduces lateral area aft. Some trim down by the stern and that increases lateral area aft. ETC. I have met a fair number of paddlers who don't want to lean their boat to control it. In fact, some prefer that the boat have insensitivity to heel so that a bit of a mistake in balance won't cause an undesired turn. All part of the "different strokes for different folks". (SNIP) > >(4) Increasing base rocker makes the boat more maneuverable with the >paddle, but decreases tracking ability. Perhaps, with all other things equal and assuming no other shape effects. One could offset the effect of rocker by decreasing beam, decreasing the block coefficient (ratio of the boat's volume to the volume of a cube having the same length, beam, and draft), deploying the skeg or using a fixed skeg or deploying the rudder. Adding rocker when one has a rudder increases the rudder's effectiveness in turning the boat. In experiments with sprint boats we found that a rudder improved performance over boats with straight keel lines aft. I believe the primary advantage had to do with the reduced wetted surface due to rocker offsetting the area of the rudder plus the rudder seemed to give the paddlers better control for wake riding etc. without upsetting their stroke cadence. Not everyone involved with the project agreed with me, however. >Based on the foregoing, it seems to me that a sea kayak should have >little if any base rocker; otherwise it will be difficult to paddle in >windy conditions without a rudder. It should also be designed so that >at high lean, it has abundant rocker and a shorter waterline. This will >permit maneuvering in tight quarters. The rudder is only used to help a >bit in windy conditions and when surfing. Not sure how much "abundant" comes to nor am I convinced that rocker means poor handling in windy conditions. Not even sure that one needs to design around the absence of a rudder. I don't feel that all the evidence has had proper evaluation yet. So many variables in this. >If the foregoing is true, why would anyone choose say a Seawards Vision >over a Seawards Navigator for sea kayaking? Ask the people who bought them. >Similarly, why do many people like the Looksha IV? >Without its rudder, it is hard to paddle in strong wind. They may have their reasons. I used to believe that no boat should need a rudder but the more I paddle and the more people I meet the more it becomes apparent to me that "no boat I paddle should need a rudder". I consider that difference significant. Cheers, John Winters Redwing Designs Web site address, http://home.ican.net/~735769 *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
part of the original email read >The rudder is only used to help a >bit in windy conditions and when surfing. maybe someone addressed this but here's my bit; windy conditions maybe depending on which quarter etc, but not in the surf. One of our big jobs here is to convince people being taught how to handle/have fun in the surf is to keep their rudder up You can't turn fast enought with a rudder in the surf, you need to be able to turn fast with a lean turn to cope with various situations. This is especially in bigger surf where it becomes a key skill to handle it safely eg in break zone to deal with rapidly steepening waves that may present a danger to you. Not only is turning with a rudder too slow, a rudder (or skeg) slows lean/paddle turns. Also a rudder can 'catch', facilitating a flip and a dunking. They can also be dangerous for fellow surfers and can be damaged in surf if you bottom the rear of your boat on the sand. As you come into shallower water of course this problem is accentuated especially if broaching - bent rudders, tipped paddlers etc. Before a surf session many in our club/group remove their rudders for these reasons. better to develop and rely on leaning and paddle skills in the surf zone. nick *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
-----Original Message----- From: dmccarty_at_us.ibm.com <dmccarty_at_us.ibm.com> I wrote: >|Putting weight forward will tend to aggravate the most common difficult >|handling situations. It may help some in headwinds but that is not a >|condition people generally have difficulty with. Be sure to try the dive >|belt in the stern though, it should reduce weatherhelm and broaching >|tendencies.. > >Hmmm. I thought I already had enough weight in my stern! 8-) > >The reason I was thinking putting the dive belt forward was to balance the load >in the kayak. Lately I've been carrying a heavy load of camera equipment in the >stern. So I figured the belt might help up front. I guess I"ll find out. I >just want to see if I can ease any tendency for the Looksha to turn into the >wind. It might help top speed to keep a level trim but more weight forward will agravate an already existing weatherhelm. If you want to cut weatherhelm put more weight in the back and less in the front. Even to keep a level (usually the fastest) trim you must be careful to not put too much weight forward. Imagine you're balancing a teeter-toter with your center of gravity (groin) over the axis (while facing one end). Any weight you put in front of your feet is a much further from the axis than what you put right behind you, so you must put a lot more weight behind you to compensate for the length of your legs to remain in balance. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
|It might help top speed to keep a level trim but more weight forward will |agravate an already existing weatherhelm. If you want to cut weatherhelm put |more weight in the back and less in the front. This explains the trip my wife and I took where we had to cross an open stretch of water, 90% of the trip was in a marsh. The trip was only a couple of miles to an island where we were setting up camp so we weren't to concerned with trim and such. But in crossing the open stretch of water a big gust caught my wifes boat and it turned like a weather cock into the wind. The problem was all the boat traffic that we were trying to avoid and the new wind generated course was not a good thing! 8-) |Even to keep a level (usually |the fastest) trim you must be careful to not put too much weight forward. |Imagine you're balancing a teeter-toter with your center of gravity (groin) |over the axis (while facing one end). Any weight you put in front of your |feet is a much further from the axis than what you put right behind you, so |you must put a lot more weight behind you to compensate for the length of |your legs to remain in balance. Ok. Makes sense to me but it never occured to me! 8-) I always have assumed that I had to much wieght toward the stern. I'll give this a try. Thanks for the help... Dan McCarty *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Hi guys, Re correcting for weathercocking, anybody ever put a continuous loop from the cockpit to the bow, and fasten a windcatching gadget (such as a small balloon) to it so that it could be run out as far forward as necessary to balance the stern's turning moment? e Elaine Harmon - eilidh_at_dc.seflin.org - eharmon_at_cs.miami.edu *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
> Hi guys, > > Re correcting for weathercocking, anybody ever put a continuous loop from > the cockpit to the bow, and fasten a windcatching gadget (such as a small > balloon) to it so that it could be run out as far forward as necessary to > balance the stern's turning moment? e > > Elaine Harmon - eilidh_at_dc.seflin.org - eharmon_at_cs.miami.edu WOW!! what a thought. a re-freshing idea, for which, i hope to read, some technical comments, from experts and folks who try strange stuff. me, i just wish i could have such ideas. b bye bye bliven - larry at foxhill_at_shore.intercom.net - not allowed to use my work _at_ *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
What people will go through to avoid using a rudder... ;) (Just kidding! The last thing I want to do is to start that discussion again) -----Original Message----- From: Elaine Harmon [mailto:eharmon_at_cs.miami.edu] Sent: Friday, October 01, 1999 10:42 AM To: dmccarty_at_us.ibm.com Cc: paddlewise_at_lists.intelenet.net Subject: Re: [Paddlewise] Rocker: too many sea kayaks Hi guys, Re correcting for weathercocking, anybody ever put a continuous loop from the cockpit to the bow, and fasten a windcatching gadget (such as a small balloon) to it so that it could be run out as far forward as necessary to balance the stern's turning moment? e Elaine Harmon - eilidh_at_dc.seflin.org - eharmon_at_cs.miami.edu *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ *************************************************************************** *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Well, my first thoughts on reading Elaine's note was..... AIR SPONSxxNS!!!!! 8-) Its Friday.... Dan McCarty What people will go through to avoid using a rudder... ;) (Just kidding! The last thing I want to do is to start that discussion again) -----Original Message----- From: Elaine Harmon [mailto:eharmon_at_cs.miami.edu] Sent: Friday, October 01, 1999 10:42 AM To: dmccarty_at_us.ibm.com Cc: paddlewise_at_lists.intelenet.net Subject: Re: [Paddlewise] Rocker: too many sea kayaks Hi guys, Re correcting for weathercocking, anybody ever put a continuous loop from the cockpit to the bow, and fasten a windcatching gadget (such as a small balloon) to it so that it could be run out as far forward as necessary to balance the stern's turning moment? e Elaine Harmon - eilidh_at_dc.seflin.org - eharmon_at_cs.miami.edu *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ *************************************************************************** *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ *************************************************************************** *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
-----Original Message----- From: Elaine Harmon <eharmon_at_cs.miami.edu> >Hi guys, > >Re correcting for weathercocking, anybody ever put a continuous loop from >the cockpit to the bow, and fasten a windcatching gadget (such as a small >balloon) to it so that it could be run out as far forward as necessary to >balance the stern's turning moment? e > We have a rotating bow line on the front of our boats and I have thought about trying that but never actually have. Also thought of a little pendant on a spring loaded bow stanchon that you could pull down with a line back to the cockpit might work. Also a litte low sail you could set up by lifting a line and having an inverted Y that hung below the line until you set it on the V of the deck. Haven't tried that either. Some have suggested attaching a weight on a rotating line inside the kayak but that would interfere with floatation and wouldn't work at all with a gear load. One popular option on our Mariner kayaks is a trim adjusting seat you can move about 6 inches fore or aft of trim. It is set up so you can move it at any time you feel the need. The foot pedals are attached to the seat so they slide as well to maintain leg length when the seat moves. There are alot of ways to skin this cat. Rudders and drop skegs are two others. We also compensate for this weathercocking effect in advance using the hull profile. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Elaine wrote; >Re correcting for weathercocking, anybody ever put a continuous loop from >the cockpit to the bow, and fasten a windcatching gadget (such as a small >balloon) to it so that it could be run out as far forward as necessary to >balance the stern's turning moment? e You might correct for the weathercocking but may do more harm than good. Weathercocking results from a combination of aerodynamic and hydrodynamic forces. As you paddle across the wind the boat gets blown sideways (called leeway) so if you kept your boat always pointing at your destination you will travel a curved course of greater distance than if you made no leeway. How much leeway you make will depend upon the windage and the lateral resistance of the boat. If you do nothing to increase the lateral resistance, adding anything above the water will increase the wind resistance and cause greater leeway. So, even though you will not turn into the wind you will have to paddle further due to the greater leeway. Even if you head above the direct course the added leeway will cause more resistance since the boat is traveling kind of crab like rather than straight through the water. Somewhere I have a report of a study of an International sailing canoe that showed a considerable increase in resistance at relatively small leeway angles of about 5 degrees. If I recall correctly it was something in the order of 40% for a boat with a centerboard down. I will dig around and see if I can find more somewhere in my stack of papers. Rudders and skegs with good airfoil shapes can help reduce leeway and weathercocking by providing some lift. Narrow deep draft hulls have greater lateral resistance and that helps too. Keels can help although the long full length keels have less effect than a short deeper keel. I have had good results with centerboards although they do take up a bit of room. The hydrodynamic aspect of weathercocking (and turning) are explained in my completely non-commercial web page at http://home.ican.net/~735769/control.htm with no advertising. Cheers, John Winters Redwing Designs Web site address, http://home.ican.net/~735769 *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
John Winters wrote: > >...<snip>... How much > leeway you make will depend upon the windage and the lateral resistance of > the boat. ...<snip>... > > ... the added leeway will cause more > resistance since the boat is traveling kind of crab like rather than > straight through the water. ...<snip>... > Narrow deep draft hulls have greater > lateral resistance and that helps too. ... All of this certainly makes sense (at least to my feeble mind). Doesn't this also imply that hulls with a single hard chine may have an advantage in such circumstances, since they tend to be more resistant to "side-slipping", thereby reducing leeway? Has anyone tested the resistance of different hull designs to slide-slipping? It would seem as though this may an important factor in "real-world" performance. As someone who paddles frequently in the wind, I do not spend much time traveling in the direction my boat is pointed. And yet the standard resistance formulas measure (or seek to measure) the resistance of a boat that is traveling straight ahead. It would be useful to know more about these other factors. Dan Hagen *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Hi guys, here's another one: with all these complicating factors of wind, current, boat design... can we always say that the most energy-efficient route from one point to another (assuming homogeneous conditions, of course) is in a straight over-the-ground course between the 2 points? It seems intuitively that it should be so, but on further thought not obvious. How about it, you physicists out there? e Elaine Harmon - eilidh_at_dc.seflin.org - eharmon_at_cs.miami.edu *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Elaine Harmon wrote: > > Hi guys, here's another one: with all these complicating factors of wind, > current, boat design... can we always say that the most energy-efficient > route from one point to another (assuming homogeneous conditions, of > course) is in a straight over-the-ground course between the 2 points? ... I have worked this out for a current (using some simplifying assumptions), but not for a side wind. The latter is more complicated, due to the slide slipping. (The current moves you sideways with the water, but not sideways relative to the water. The wind blows you sideways relative to the water, in addition to the former.) In the simpler case of a current, there are some circumstances where you are better off if you do not ferry across, but instead paddle with your boat pointed straight across and then paddle forward along the bank into the current to recover from your sideways drift. When would this be true? The following draws from my earlier posting on this subject: For the case of a current with uniform strength, my very rough model suggests that the break-even point is for a ferry angle of about 57 degrees, which occurs when the ratio of paddling speed to current speed is approximately 1.19. In other words, if you can paddle more than 19 percent faster than the current, your ferry angle will be less than 57 degrees, and it will take less time to ferry across than to paddle at a straight-across heading (with zero ferry angle, followed by a paddle up current). On the other hand, if your paddling speed is less than 19 percent faster than the current, your ferry angle would have to exceed 57 percent, in which case it will take you less time if you paddle a straight-across heading (zero angle), even though you have to paddle up current once you reach the other side. Now for the math! Using some fairly straightforward trigonometry, it can be shown (if I haven't made an error) that the ratio of the straight-angle time (including the up-current paddle) to the ferry-angle time, st/ft, equals (1+c/p)cos(a), where "c" is the speed of the current, "p" is the paddling speed, and "a" is the ferry angle (in degrees) which itself is a function of c/p. The necessary ferry angle "a" equals the inverse sine of c/p. In other words, the time ratio st/ft is a function only of c/p. This ratio equals one when c/p is approximately equal to .83867, which corresponds to a ferry angle of 57 degrees. If the ratio c/p exceeds .83867 (i.e., if p/c is less than 1.1924), then st/ft is less than one and ferrying will actually take more time than paddling at a straight-across heading, even though you have to paddle up current. (I have checked this against a few simulations, and this seems to work, but as always someone should check the math...) Next time you have to cross a current, ask yourself if you can paddle more than 19 percent faster than the current. If so, then you MIGHT save time by ferrying. I say that you might save time, because the above analysis assumes a current of constant strength. But I have never seen such a current. It is typically slower near shore, even in the absence of eddies. And with eddies it is, of course, a whole new ballgame. So actually, it is quite a bit more complicated than in the simple model above (it always is). Add your own fudge factor to the 19 percent rule. But perhaps the above "rule" provides a crude staring point. I would certainly welcome a more complex model, if someone knows of one or has the desire to develop one. Again, the case of a side wind would be more complicated. But given that ferrying is not always faster for a side current, the same may be true in the case of a side wind--but the parameters would certainly change. Dan Hagen *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Elaine Harmon wrote: > Hi guys, here's another one: with all these complicating factors of wind, > current, boat design... can we always say that the most energy-efficient > route from one point to another (assuming homogeneous conditions, of > course) is in a straight over-the-ground course between the 2 points? It > seems intuitively that it should be so, but on further thought not > obvious. How about it, you physicists out there? e Oh-oh!! Sounds like another brachistochrone problem! Can this result in the invention of a form of mathematics more intimidating than the calculus of variations? Where are the Newtons, Liebnitzs, Bernoullis? Gak, where is Inverbon? Mike Actually, David Burch's book on kayak navigation covers wind and current effects on the paddler and how to "best" handle them. However, I don't think it's worked out on the basis of a minimum energy path. Note that minimum energy path isn't necessarily the same as minimum time or minimum paddle force, so it may not always be appropriate for all paddlers. For example, minimum energy requiring a really high stroke force for a short period (i.e. a _hard_ sprint) may be outside the abilities of all but an Olympic class paddler. Energy is always harder to work with than force or momentum. Too many sources of energy loss to mess up the calculations. My years of engineering etc tells me not to touch this one and just enjoy the paddling. *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
-----Original Message----- From: 735769 <735769_at_ican.net> John Winters wrote <SNIP> >Somewhere I have a report of a study of an >International sailing canoe that showed a considerable increase in >resistance at relatively small leeway angles of about 5 degrees. If I recall >correctly it was something in the order of 40% for a boat with a centerboard >down. I will dig around and see if I can find more somewhere in my stack of >papers. > >Rudders and skegs with good airfoil shapes can help reduce leeway and >weathercocking by providing some lift. Easy to see a rudder reducing weathercocking. Its harder to see how it reduces leeway if it is way back on the stern. I can see a rudder might help reduce leeway a little on a boat that weatherhelms but it would seem to add leeway to a boat with a lee helm (to correct you would swing the stern further downwind). Since your point seems to be that a kayak may have considerable added drag due to the somewhat crablike motion of leeway (at least a sailboat with a centerboard may exhibit this) and that a rudder can reduce the leeway it appears you are implying there will be less drag in a side wind if you have a rudder. I think finding an example from canoes, kayaks or even ships would be more relevant here since most kayaks don't have a large centerboard to confound things. It seems to me that the rudder will create more drag for several reasons. It is adding wetted surface just by being there (Sea Kayaker Magazines 1986 towing tank tests showed 10% more drag at 3 knots--going in a straight line). If the rudder was fixed (like a skeg) the kayak's leeway will mean the rudder/skeg is moving at an angle and therefore sweeping out a wider chunk of water than its thickness (this is probably also the reason the centerboarded sailing canoe might--if you are correct--add so much drag due to 5 degrees of leeway). If the rudder is angled to correct for weatherhelm then it is now sweeping out an even wider swath through the water adding even more drag (if correcting for lee helm the angle would be less than that just due to leeway on a skeg and that should reduce drag). In "Ships in Rough Water" Kent says that the rudder becomes the major retarding force on a merchant ship when it is angled enough to correct for weatherhelm in gale force sidewinds. More drag due to the rudder than all other forms of resistance combined. WOW! Somehow I don't think the rudder reducing leeway a bit has helped much here. More subjectively, the other day I was paddling a kayak that tended to yaw but the center of gravity kept going in the direction it had been going in originally so the kayak kind of skidded sideways at a noticeable angle (maybe 10 to 15 degrees). It seemed to do this without slowing down very much so I don't think there was much added drag due to crabbing to the side a little bit, certainly not anywhere near 40%. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Matt Broze http://www.marinerkayaks.com -----Original Message----- From: Dan Hagen <dan_at_hagen.net> SNIP> >All of this certainly makes sense (at least to my feeble mind). Doesn't >this also imply that hulls with a single hard chine may have an >advantage in such circumstances, since they tend to be more resistant to >"side-slipping", thereby reducing leeway? Has anyone tested the >resistance of different hull designs to slide-slipping? I timed myself over a short distance while skulling various kayaks sideways as fast as I could (for 20 to 30 seconds). I think your guess is correct about hard chines, the sides are more vertical and if you lean the kayak you dig the chine in deeper increasing the size of the underwater profile. I tried long boats and short boats, hard chined and round bilge boats, narrow and wide boats. My goal was to beat Olympic gold medalist Greg Barton in a short fun race at the Port Townsend symposium that had a backwards and sideways leg. If you want to go sideways faster go with round bilges and a wider kayak. Length didn't seem to make much difference. The added length may be being made up for the by the shallower draft at the same dispalcement. Most important though is to find a kayak with the center of lateral resistance at your side so the kayak will go straight sideways rather than yaw (so the bow or stern takes the lead). Yawing in this situation is very hard to correct for. It would seem as >though this may an important factor in "real-world" performance. As >someone who paddles frequently in the wind, I do not spend much time >traveling in the direction my boat is pointed. And yet the standard >resistance formulas measure (or seek to measure) the resistance of a >boat that is traveling straight ahead. It would be useful to know more >about these other factors. > >Dan Hagen >*************************************************************************** >PaddleWise Paddling Mailing List >Submissions: paddlewise_at_lists.intelenet.net >Subscriptions: paddlewise-request_at_lists.intelenet.net >Website: http://www.paddlewise.net/ >*************************************************************************** *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Dan wrote; (SNIP) >All of this certainly makes sense (at least to my feeble mind). Doesn't >this also imply that hulls with a single hard chine may have an >advantage in such circumstances, since they tend to be more resistant to >"side-slipping", thereby reducing leeway? Off the cuff I would think, yes. However, (ain't there always a "however"?), it would depend upon chine height, chine depth at the ends, flare of sides, and maybe a lot of ETC's. If I use my program for controllability I can get the same lateral resistance in both round bilge and hard chine configurations. Of course, stability, resistance ETC. vary so you have to decide what characteristics you want to hold constant. For example, a wide shallow hard chine boat might not have as much lateral resistance as a narrow deep round bilge boat. But at that point you have to ask if the comparison makes sense. In one of my curious modes I created a generic boat with hard chines. I then created a similar boat with a round bilge but same beam, length displacement etc. The round bilge boat had one square foot less wetted surface than the hard chine boat so one could easily add more lateral plane area to achieve more lateral resistance while maintaining similar resistance to forward motion. Then I increased the draft of the round bilge boat until it had the same wetted surface as the hard chine boat (length etc. remaining equal) and was able to increase the lateral plane by 0.35 sq.. ft. No telling how this deep boat would handle but it serves to show how complex things can get. >Has anyone tested the >resistance of different hull designs to slide-slipping? Not me. At least not in a way that I would publish as gospel. Nevertheless, one might apply data from sailboats and see what happens. >It would seem as >though this may an important factor in "real-world" performance. As >someone who paddles frequently in the wind, I do not spend much time >traveling in the direction my boat is pointed. And yet the standard >resistance formulas measure (or seek to measure) the resistance of a >boat that is traveling straight ahead. It would be useful to know more >about these other factors. Absolutely. I have read some information on added resistance due to leeway but nothing I felt I could apply to canoes or sea kayaks with any reliability. I have tried measuring leeway with poor success because I cannot separate paddling influences from wind and boat influences. Some of the most informative stuff I have read and heard comes from windsurfers who use different skegs for different conditions. (would sea kayakers would balk at buying a selection of skegs at about $100.00 a pop). Cheers, John Winters Redwing Designs Web site address, http://home.ican.net/~735769 *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
I have a "correction" to the math that I posted below. Dave Kruger (bless his heart) decided to take me up on my request that someone check my math. He could not get my result, for the very good reason that there is an "inconsistency" between my description of the problem and my result. (How's that for spin? My answer was correct, but only if I redefine the problem a bit. :-)) I stated before that my result was for the case where there is no shoreline eddy protecting you from the current when paddling along the bank. But in trying to determine why Dave got a different answer, I discovered that my earlier formula is for the case where there *is* protection along shore from the current, allowing you to paddle forward along the bank at your paddling speed of "p" (as opposed to p-c, where c is the speed of the current in the channel). So here is a simple, new-and-improved summary of the two cases for st/ft, the ratio of the straight-angle time (including the upstream paddle) to the ferry-angle time: CASE 1 (new-and-improved description): This applies when there is a constant paddling speed, a constant current speed away from the bank, and a protective "eddy" (with zero current speed) next to the bank. FORMULA (as before): st/ft = (1+c/p)cos(a), where "a" is the ferry angle (in degrees), which equals the inverse sine of c/p. BREAKEVEN POINT for ferrying (as before): When "p" (your paddling speed) exceeds "c" (the current speed) by 19%, st/ft=1. If p exceeds c by more than 19 percent, ferrying will be faster (for a given paddling speed). CASE 2: This applies when there is a constant paddling speed, a constant current speed away from the bank, and NO protective eddy (current speed equals c along the bank as well as in the channel). FORMULA (new and improved): st/ft = {1 + 1/[(p/c)-1]}cos(a), where a is as defined above. BREAKEVEN POINT for ferrying: In this case there doesn't seem to be one! It is always faster to ferry across. (I will have to double check this.) I think that the above is correct, but as always it needs to be verified by someone else. Obviously there are many other cases as well. An interesting case might be to determine at what ratio of along-shore current to primary current there exists a potential savings from avoiding a ferry. This would of course depend on the ratio c/p as well. Dan Hagen Dan Hagen wrote: > > > I have worked this out for a current (using some simplifying > assumptions), but not for a side wind. The latter is more complicated, > due to the side slipping. (The current moves you sideways with the > water, but not sideways relative to the water. The wind blows you > sideways relative to the water, in addition to the former.) In the > simpler case of a current, there are some circumstances where you are > better off if you do not ferry across, but instead paddle with your boat > pointed straight across and then paddle forward along the bank into the > current to recover from your sideways drift. When would this be true? > The following draws from my earlier posting on this subject: > > For the case of a current with uniform strength, my very rough model > suggests that the break-even point is for a ferry angle of about 57 > degrees, which occurs when the ratio of paddling speed to current speed > is approximately 1.19. In other words, if you can paddle more than 19 > percent faster than the current, your ferry angle will be less than 57 > degrees, and it will take less time to ferry across than to paddle at a > straight-across heading (with zero ferry angle, followed by a paddle up > current). On the other hand, if your paddling speed is less than 19 > percent faster than the current, your ferry angle would have to exceed > 57 percent, in which case it will take you less time if you paddle a > straight-across heading (zero angle), even though you have to paddle up > current once you reach the other side. > > Now for the math! Using some fairly straightforward trigonometry, it can > be shown (if I haven't made an error) that the ratio of the > straight-angle time (including the up-current paddle) to the ferry-angle > time, st/ft, equals (1+c/p)cos(a), where "c" is the speed of the > current, "p" is the paddling speed, and "a" is the ferry angle (in > degrees) which itself is a function of c/p. The necessary ferry angle > "a" equals the inverse sine of c/p. In other words, the time ratio > st/ft is a function only of c/p. This ratio equals one when c/p is > approximately equal to .83867, which corresponds to a ferry angle of 57 > degrees. If the ratio c/p exceeds .83867 (i.e., if p/c is less than > 1.1924), then st/ft is less than one and ferrying will actually take > more time than paddling at a straight-across heading, even though you > have to paddle up current. (I have checked this against a few > simulations, and this seems to work, but as always someone should check > the math...) > > Next time you have to cross a current, ask yourself if you can paddle > more than 19 percent faster than the current. If so, then you MIGHT save > time by ferrying. I say that you might save > time, because the above analysis assumes a current of constant > strength. But I have never seen such a current. It is typically slower > near shore, even in the absence of eddies. And with eddies it is, of > course, a whole new ballgame. So actually, it is quite a bit more > complicated than in the simple model above (it always is). Add your own > fudge factor to the 19 percent rule. But perhaps the above "rule" > provides a crude staring point. I would certainly welcome a more complex > model, if someone knows of one or has the desire to develop one. > > Again, the case of a side wind would be more complicated. But given that > ferrying is not always faster for a side current, the same may be true > in the case of a side wind--but the parameters would certainly change. > > Dan Hagen > > *************************************************************************** > PaddleWise Paddling Mailing List > Submissions: paddlewise_at_lists.intelenet.net > Subscriptions: paddlewise-request_at_lists.intelenet.net > Website: http://www.paddlewise.net/ > *************************************************************************** *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Matt Broze wrote: >It seems to me that the rudder will create more drag for several reasons. It >is adding wetted surface just by being there (Sea Kayaker Magazines 1986 >towing tank tests showed 10% more drag at 3 knots--going in a straight >line) <<snip>> Does a drop skeg (below the waterline, obviously) have as much drag as a rudder (which is at the waterline and behind the boat's wave) due to the added wetted surface? Shawn -- 0 ____©/______ ~^~^~^~^~^~^~^~^\ ,/ /~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^ Shawn W. Baker 0 http://www.missoulaconcrete.com/shawn/ Baker Brothers mailto://baker_at_montana.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
-----Original Message----- From: Shawn W. Baker <baker_at_montana.com> ><<snip>> > >Does a drop skeg (below the waterline, obviously) have as much drag as a >rudder (which is at the waterline and behind the boat's wave) due to the >added wetted surface? There are a lot of variables and even if we use the same shape, size, stiffness etc. the fact that one of them pierces the water and the other has a junction with the hull and a now open skeg box behind it will complicate things as all of those things can add drag. Hard to say which will add the most. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Shawn wrote; >Does a drop skeg (below the waterline, obviously) have as much drag as a >rudder (which is at the waterline and behind the boat's wave) due to the >added wetted surface? First, rudders need not have more surface area that skegs. Many do but that does not mean they have to. In general surface piercing foils cause more drag than equivalent area rudders suspended below the boat. Rudders suspended below the boat can experience increased drag due to the flow between the rudder and the hull so in sprint boats and rowing shells they try to get as tight a fit as possible between hull and rudder. Of course, builders have tried just about every configuration imaginable and you can't get them to agree on much. :-) Large open trunks cause greater drag with skegs but you can get around this in several ways. 1. You can use a skeg that keeps the slot full at all times. 2. You can use some form of seal like they use on sailboats (not a great idea on sea kayaks to my mind) 3.You can mount the skeg at the stern with the trunk exiting through the radius at the stern. The latter works because the flow at the stern has gone turbulent and even travels in the same direction as the boat so no increase in drag occurs. At one yacht company where I worked some felt the open trailing edge could reduce drag by reducing the suction at the stern. Well, Maybe. Someone may know of more ways. ETC. Cheers, John Winters Redwing Designs Web site address, http://home.ican.net/~735769 *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
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