In response to previous post on a Frenzy I went to the Ocean Kayak site to check out some sizing info. While there I wandered over to their kayak design section and found some info on hull shape. My reading of what they wrote was Flat bottomed kayaks are less initially stable in flat water than V bottomed kayaks. Flat bottomed kayaks have more secondary stability than V bottomed kayaks. Flat bottomed kayaks are more stable in surf than V bottomed kayaks. A "U" shaped bottom is equated to a flat bottom. I would think "U" would be a rounded hull and be more on the other sided of stability from a "V" hull rather than same as a flat bottom. This does not seem to go with what I remember reading about hull shapes. Is my memory bad, did I mis-read what was on the Ocean Kayak site, or is their information contrary to conventional thinking.? Would appreciate any thoughts on the matter. Note: I was going to copy their exact comments into this message, but did not because of potential copywrite problems. Mark J. Arnold *************************************************************************** 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/ ***************************************************************************
"Mark Arnold" <mjamja_at_earthlink.net> wrote: SNIP >Note: I was going to copy their exact comments into this message, but did not because of potential copywrite problems. Er, I think you meant copyright:-) FYI, it's pefectly acceptable to quote short passages verbatim from other people's writing in order to comment on them (or, as in this case, to invite comment on them). This is called "fair use." What's not legal or moral is pass off other people's writing as your own, or use huge chunks of it to pad out your own spindly work. In this case, it might be best to quote exactly, out of fairness to your source, so that what they said is accurately represented, and not, however unintentionally, twisted. That way, the pundits on our list can respond to what they actually said, and not what someone thought they said... And now, let the U-hull debate begin... Philip (Who writes for a living, and is always flattered when people quote him, even if it's just to point out what a doofus he is - hey, it means they're reading me...) *************************************************************************** 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/ ***************************************************************************
It is awfully enticing to look for blanket statements or generalized rules-of-thumb for determining stability by inspection of hull shape. Unfortunately, it is not that easy. "V" bottoms can be stable or unstable. Flat bottoms can have high initial stability, but low secondary. Round bottoms can have any stability characteristic you want. This is because stability is largely a function of what happens right at the water surface. The bottom shape will have little effect until it is at the water surface. Stability is also a function of the height of the center of gravity. Bottom shape will only effect this to the extent that it permits the seat to be placed low or high in the boat. On Aug 19, 2005, at 9:31 AM, Mark Arnold wrote: > In response to previous post on a Frenzy I went to the Ocean Kayak > site to check out some sizing info. While there I wandered over to > their kayak design section and found some info on hull shape. My > reading of what they wrote was > > Flat bottomed kayaks are less initially stable in flat water than V > bottomed kayaks. > Flat bottomed kayaks have more secondary stability than V bottomed > kayaks. > Flat bottomed kayaks are more stable in surf than V bottomed kayaks. > A "U" shaped bottom is equated to a flat bottom. I would think "U" > would be a rounded hull and be more on the other sided of > stability from a "V" hull rather than same as a flat bottom. > > This does not seem to go with what I remember reading about hull > shapes. Is my memory bad, did I mis-read what was on the Ocean > Kayak site, or is their information contrary to conventional > thinking.? > > Would appreciate any thoughts on the matter. > > Note: I was going to copy their exact comments into this message, > but did not because of potential copywrite problems. Nick Schade Guillemot Kayaks 824 Thompson St Glastonbury, CT 06033 USA Ph/Fx: (860) 659-8847 http://www.guillemot-kayaks.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/ ***************************************************************************
Commenting on Nick's and Marks comments about stability and shape, I have a simple approach that seems to work pretty well. Right now I am working on a plug for an 18 foot 22 inch boat and have been looking into what I want the boat to do. When the boat is placed on edge, the amount of volume increase under water by the side that enters, will contribute to the restoring force. A round hull will not add any volume in the water when placed on edge. A wide flat hull will add a lot of volume and will displace so much water and create a large restoring force. A V hull will be somewhere in between, as well as a combination of shapes between the totally round and the totally square. Extremes are: round to give zero support, and square to give maximum support. On the other hand a round hull will be faster since it has the minimum wetted surface. The square hull will be the slowest. So the compromise is always in between. Round means less stable, less maneuverable by edging. Sharp on extremes and flat at mid ship seems the best compromise for cutting water but obtaining stability and maneuverability. Epic 18, has pretty round hull, almost olympic shaped, is very fast, but needs a rudder for sure, and feels tippier. Silhouette is very fast, with almost rounded bow and stern, both ending sharp, and with some widening and flattening in the middle, and hard chines. It is very fast but hard to maneuver. Then the Legend, the Greenlander Pro or the Point Bennet, keep a sharp bow and stern, V continuation bending to become quite flat a mid ship with almost vertical side walls and hard chines. They are fast, but very maneuverable and more stable. The same trend can be seen in some of the Current Design boats, like the Slipstream and the later models. I have two boats with the same seam width. One has the hull with higher angle walls, soft chines and slight V. It is reasonably stable, very good maneuverability, good tracking and reasonable speed. The other, with the same bow and stern, and seam shape, but with vertical walls, hard chine and almost flat bottom is tremendously stable, slower, but very easy to turn with the slightest edging. This is in agreement with the concept of rounder is faster, less stable and less maneuverable. Just my observations. Best Regards, Rafael Mexico. *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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