Nick wrote: > My responses on this have largely been pushed by advertising hype I read > and conversations I hear. It is quite common to hear something to effect > of "With it's AAAA chine this boat has XXXX stability." or "I paddled X > hard chine boat and Y soft chine boat and the soft chine boat was much > more ZZZZ". My goal is for people to take these broad sweeping statements > with a grain of salt. They usually completely ignore important design > characteristics that are much more important. Nick is dead on here. When I first got into designing canoes and kayaks one would hear tons of nonsense. I am not sure it is better now despite the efforts of some designers. We still have salespeople who make extravagant and unsupported clams about boats. I suppose it reveals the triumph of ignorance and superstition over science. :-) Fortunately, here on Paddlewise we are smarter than the average paddler (well, we try) and can deal with the straight goods without sugar coating. Some of the discussions here have been highly educational. Some of you will recall such topics as whether paddles moved or not, the effectiveness of paddle shapes, the sponson issue (I think we can spell it out now :-) ), to rudder or not to rudder, etc. etc. All good stuff. 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/ ***************************************************************************
I'm mostly in agreement with Robert Livingston concerning what he wrote regarding primary and secondary stability. Certainly there is no official or even a generally accepted definition of "Secondary Stability" in Naval Architecture or even kayaking. In fact, the words seem to rarely be used together outside of the Kayak and Canoe realm. I put "secondary stability" into Google and with the exception of a few mentions in relation to dental materials and one concerning fluid mechanics and Gortler vortexes (which I have never heard of couldn't understand at all upon viewing the article) the vast majority of the first one hundred Google results seemed to be related to kayaking or canoeing. This brings up a question. Who first used this term and when? Let's see who among Paddlewiser's can find the earliest documented example of this term used in relation to boats. Given its present usage level of usage there, I suspect it will be in the realm of canoeing or kayaking. I've been looking at our earliest brochures and see that I used the term in the very earliest Escape brochure we printed (probably in early 1982). By the next printing of the Escape brochure though, I wrote about "dynamic stability in waves" instead. (That turned out to be a mistake, as I found out much later, there already was a defined term in Naval Architecture for "dynamic stability" and it doesn't mean what I had meant. Such is the hazard of making up terms and then not researching them I guess. I can't remember where I may have gotten the "Secondary Stability" term but I looked to see if I can find it in John Dowd's or other early sea kayaking texts. Perhaps it was just the obvious term to make up to separate it from "Primary Stability" and I made that up like I did with "Dynamic Stability". [I couldn't find the term in any of John Dowd's many editions, but I found that Randel Washburne called it "large-angle stability" in his 1983 "The Coastal Kayaker" book). I'll try to look at some mid 1970's and later Canoe magazine buyers guides and early British kayaking books (when I get back to work) to see if it was used there at all. I liked Robert's example of pushing against a door with someone pushing back. My one nit-picking point of disagreement comes with his interpretation of where on the curve the decrease in pushing back is important. In the Sea Kayaker comparison and explanation of the stability curves the term stiffness is used (this article is probably most easily found in its entirety on our website--near the end of the Mariner XL review--unless one happens to have the Spring 1987 issue). Here is part of what is written there (used with permission): "At any selected point on these curves the righting moment measured in lbs.ft. may be read on the vertical axis, and the angle of inclination measured in degrees on the horizontal axis. The area under the curve to that point represents the work done in inclining the kayak to that angle and, if the angle is measured in radians (1 radian = 57.30 ), the units of work will be directly in ft.lbs. The slope of the rising part of the curve at that point represents the stiffness, which is the rate of increase of the righting moment as the angle of inclination increases. Units of stiffness come out as lbs.ft./degree. For a boat to be in a stable state, an increase in heeling force must be balanced by an increase in righting moment, after an appropriate increase in inclination. So stability requires stiffness and the two terms are often interchanged. The slope of a curve can be derived at any desired point by drawing a tangent at that point, and that is a straight line coincident with the curve at the point of contact. Its value can be calculated by making a right angled triangle from this tangent and dividing the vertical height by the horizontal length." Apparently, the guy on the other side of the door varies in strength (to resist) in relation to the angle you swing open the door and at some point if you get enough angle on him he can be overpowered and you will likely fall through that door when that happens (unless you can suddenly quit pushing). This surely will happen at the top of the curve. I contend that, due to momentum, the kayaker is likely to feel about to capsize when the angle of the stiffness curve begins to significantly decrease (even though it is still rising). One other nit-picking point, while hull's width is an important parameter to initial stiffness it is not as significant a factor as the area of the water plane in determining stability. (This applies to stiffness at any point of lean). With two boats of the same width with vastly different water planes the one with the most water plane area at a given angle will be the stiffest at that point of the curve. Imagine a hollow diamond shaped water plane compared with a full rounded shape of the same length and width. Since longer length also increases the water plane, longer length increases the static stability of the kayak if width and other factors are held constant. How about this for a simple definition of secondary stability: "The stiffness against further angle of tilt when the hull is already tilted to three-fourths of its maximum righting moment divided by the hulls initial stiffness." I invite refinements (and simplifications of terms). The goal will be to get to a definition that matches the subjective feel experienced by a paddler but while using measurable and well defined parameters. Robert wrote: <Snip>>>>>>>As for "secondary stability" since that has no "scientific" definition, I cannot make the same statement. But the effect of width on the entire curve of stability is so paramount that again it is hard (impossible?) to find any "commercial-like" design where the stability curve for 0 to 45 degrees will be greater at ANY point than a commercial-like design with a waterline width that is 1 inch greater.<<<<<Snip> I'm afraid a little more nit-picking follows (or at least some contrary evidence that argues against Roberts challenge). The Nimbus Puffin was 7/8" narrower in max. beam than the Aquaterra Chinook. Lengths and prismatic coefficients were about the same. The Chinook was a little more initially stable but if you get the Winter 1986 edition of Sea Kayaker you can see that the curves overlap at 17 to 18 degrees of tilt (both are still ascending) so that at all angles of lean well above 18 degrees the Puffin has far greater stability. The Puffin was 1 3/8" (one and three eights inch) narrower at the waterline as well. The Puffin has much fuller bilges and the Chinook tends to more approach John Winters' V-bottom computer model (where the chines were at the surface). Sea Kayaker placed the center of gravity of 150 pounds (representing the paddler) 10" above the seat bottom when measuring a kayaks stability (with a torque wrench). Perhaps the seat height was higher in the Chinook (Sea Kayaker didn't publish the seats height at that time). The flatter bottomed Sea Runner (in the same issue) was 1" narrower than the Chinook in beam (3/4" narrower at the waterline) but had far greater stability than either the Chinook or Puffin. Another possible confounding factor could be the height of the gunnels. Higher gunnels will have better stability at high angles of lean. The Sea Runner holds its width over more of its length than does the Chinook and has a much flatter bottom. Same caveat about the seat height as before. I should state that these were measured in a tank (rather than computer modeled) results so there is greater chance that some measurement error was involved. My point is that width isn't the whole story even when we are just considering a kayaks static stability. 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/ ***************************************************************************
> Sea Kayaker placed the center of gravity of > 150 pounds (representing the paddler) 10" above the seat bottom when > measuring a kayaks stability (with a torque wrench). Perhaps the seat height > was higher in the Chinook (Sea Kayaker didn't publish the seats height at > that time). That is the problem with that early Sea Kayaker data. My challenge applies to a case where the center of gravity above the bottom of the boat (or the waterline if preferred) is the SAME. If you measure from the top of the seat, then, of course, all bets are off as it depends on the height of the seat. It turns out that very slight changes in the height of the center of gravity make a big difference in the curves. As Winters points out, this has to be held constant.* I will stick with my contention that the width is paramount if the height of the center of gravity is the same for the kayaks being compared. Counter-examples where the height of the center of gravity is different or "unknown" do not count. :) >Imagine a hollow diamond shaped water plane >compared with a full rounded shape of the same length and width. Since >longer length also increases the water plane, longer length increases the >static stability of the kayak if width and other factors are held constant. I agree that the water plane makes a difference. The hollow diamond shape will be less stable for a given width. My contention is that the width is more important. An inch of extra width will trump the water plane every time. I would concede to Matt that the length of the boat is going to make a difference and I sort of glossed over this. Long boats, for a given width, will tend to be more stable. If you are going to try and find a commercial design that is an exception to the rule that wider (by 1 inch) is always more stable it would be comparing a hollow diamond very short kayak with a "full" shaped very long kayak. It would require a dramatic difference in length however to sway the numbers. ___________________________________________________________ * Even now that Sea Kayak publishes the height of the seat, I have never "liked" the approach of measuring from the height of the seat because designers who put higher seats in are going to be "punished" in the sense of having their boats look less stable. Another kayak with a very low seat will look more stable although the seat may be so low that everyone who actually buys that boat ends up installing a nice thick foam cushion to raise themselves up a bit. *************************************************************************** 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/ ***************************************************************************
While not being of "scientific and technical" mind set, it would seem to me that "stability" is a relative term and dependant entirely on the paddler's perception. For instance, a landlubber would percieve any kayak to be unstable. In addition, the weight distribution of the paddler him/her self also affects stability as does the paddling circumstances on any given day (flat water as opposed to rough). Most paddlers just want a boat they are "comfortable" in. Nancy K. *************************************************************************** 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/ ***************************************************************************
Rev. Carter wrote: <Snip>>>>>>I paddle an Arluk III which is 18 feet long and 21 inches wide and to me it is a "stable feeling" boat.<<<<<Snip> Bob, are you sure it is an Arluk III you have? Sea Kayaker measured the Arluk III at 23" wide when they tested it. Several sources say the Arluk II was 22" wide. The Arluk I (the original one of the series not the slightly later fun racing kayak that came out in 1987--hardly any were made of the original 1984 Arluk) was 20.5" wide. That round bottom made it feel a lot tipper than a Nordkapp to me (the Arluk II felt more like a Nordkapp in stability). Here I go.....nit-picking again. Nick wrote: >>>>>>>There are lots of characteristics effecting the stability, yet people tend to focus on chines for some reason.<<<<< Ain't that the truth! I'd guess that it is because it is a difference they can see with their own eyes without even having to measure. >>>>Next time a sales rep says "The chine shape of this boat gives it good initial stability." say to him: "Chines have nothing to do with initial stability. The shape of the waterplane is more important. " and see what he says.<<<<<< It will just piss them off. Matt Broze 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/ ***************************************************************************
Now you have got me wondering. The boat is labeled "Arluk III" and when I bought it at REI back in 2001 their data sheet listed it at 21" wide. Oh well. Thanks for nit picking By the way I was in Seattle this week and it was sad to see your shop closed. Hope you are getting time to paddle now. Bob > Rev. Carter wrote: > <Snip>>>>>>I paddle an Arluk > III which is 18 feet long and 21 inches wide and to me it is a "stable > feeling" boat.<<<<<Snip> > > Bob, are you sure it is an Arluk III you have? Sea Kayaker measured the > Arluk III at 23" wide when they tested it. Several sources say the Arluk > II > was 22" wide. The Arluk I (the original one of the series not the slightly > later fun racing kayak that came out in 1987--hardly any were made of the > original 1984 Arluk) was 20.5" wide. That round bottom made it feel a lot > tipper than a Nordkapp to me (the Arluk II felt more like a Nordkapp in > stability). Here I go.....nit-picking again. *************************************************************************** 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/ ***************************************************************************
Bob Carter wrote: >>>By the way I was in Seattle this week and it was sad to see your shop closed. Hope you are getting time to paddle now.<<<< Did you actually come by the store? Our store is still here and we are usually open during our old regular store hours, 11--6:30 T-F & 10-5 Saturday (although we now suggest calling first to be sure of that before going out of your way to come down here just in case we aren't). We had hoped to be gone by now but finishing the huge backlog of orders from last year have trapped us here probably at least through this summer. There is always still the possibility that someone else will keep the store open later so I wouldn't go around telling people that we are closed quite yet anyway. Matt Broze 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/ ***************************************************************************
I came by last tuesday afternoon about 3pm. Sorry I missed you. Bob ----- Original Message ----- From: "Matt Broze" <mkayaks_at_oz.net> Subject: Re: [Paddlewise] Stability > Bob Carter wrote: >>>>By the way I was in Seattle this week and it was sad to see your shop > closed. Hope you are getting time to paddle now.<<<< > > Did you actually come by the store? Our store is still here and we are > usually open during our old regular store hours, 11--6:30 T-F & 10-5 > Saturday (although we now suggest calling first to be sure of that before > going out of your way to come down here just in case we aren't). We had > hoped to be gone by now but finishing the huge backlog of orders from last > year have trapped us here probably at least through this summer. There is > always still the possibility that someone else will keep the store open > later so I wouldn't go around telling people that we are closed quite yet > anyway. > > Matt Broze > 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/ ***************************************************************************
This archive was generated by hypermail 2.4.0 : Thu Aug 21 2025 - 16:33:41 PDT