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Kayak and Canoe Design Bulletin Board
Re: Wide sterns
Posted By: Sam McFadden In Response To: Re: Wide sterns *Pic* (Nick Schade - Guillemot Kayaks)
Date: Monday, 17 June 2002, at 4:01 p.m.
: I had been thinking about this kind of shape for a while. I ended up building
: the Aleutesque because what I had drawn up looked so cool I figured it
: would be worth it even if the performance was not great.: But I did have a theory going into it. A "transom" stern may have
: the effect of making the boat appear longer in the water than it actually
: is. At speed the water just sheets of the end (like it is planing) and
: leaves a depression in the water that acts like part of the hull as far as
: the wave making is concerned. I don't know if this really works, but it is
: the theory.: This also lets me keep the width of the boat farther aft which like Hans
: suggested improves the stability in an otherwise narrow boat.: I do think that on a big wave the full stern section should help support the
: boat to the point that it may actually plane. However, it is possible that
: there is so much lift in the stern that it keeps the boat quite flat,
: which may force the bow down into the water ahead of the wave. This would
: be particularly true on short wavelength surf. The result may be that the
: boat has a tendancy to perl or broach.: I need to try the boat in something other than flat water to get a better
: feel for the answers to some of these questions.
Thanks Nick,Wow - that’s wild!! Does the aft edge submerge? I hope you will treat us to more photos.
Your thoughts on full stern sections helping to plane sound good. Since my curiosity about this sort of shape comes from sailing, I’m trying to be careful. Because kayaks don’t have sails, keels, and rudders there is a lot of opportunity for me to be confused about the cause of a particular type of motion. However, when sailing downwind, there is often a telltale lift of the stern and drop of the bow that signals catching a wave. The sailboats that don’t go fast downwind feel more like kayaks to me in the way they respond to following seas. Of course there is a big power difference in the comparison here – I recall you commented once that this tends to happen more when the paddler is tired. This is also the same sort of behavior that makes a boat feel safe in waves.
My concern about the tracking of a wide stern boat came from trying to keep the shape from looking too blunt. The extreme opposite of the transom stern would be a no-rocker, plumb stern where the displaced water comes together mostly in the vertical plane. With a transom, the displaced water comes together mostly in the horizontal plane. Is that related to your thoughts on the boat appearing longer than it actually is? I tended to make the slope of the buttocks shallow, resulting in lots of rocker and little lateral projected area aft. I also had trouble deciding how much to lift the lower edge of the transom above the static waterline so that in flat water with a stern wave and a little squatting, the boat wasn’t dragging the transom.
Thanks for the comments,
Sam
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