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Kayak and Canoe Design Bulletin Board
Re: How long is too long?
Posted By: Steve McDonald In Response To: How long is too long? (Tom Jarecki)
Date: Saturday, 9 October 1999, at 1:41 a.m.
> I'm looking at building a racing kayak for mainly flat water races where
> the paddling is one leg in a multi-sport adventure race. I wish to keep up
> with (or beat!) the guys and gals on surf skis, but I don't have $2400
> (Canadian) to buy one for myself. The CLC Patuxent 19.5 looks like the
> simplest way to get a fast kayak but I was wondering about stretching it
> by about 1.5 feet to increase the waterline to about 20.5 feet, and also
> narrowing it to 19" (from 21). So far so good, no problems that I can
> see with this design-wise or structurally.> However, I got to thinking about horsepower and at what point does a
> waterline become so long that a recreational athlete (me - 5'-11",
> 180#, strong upper body) can no longer achieve hull speed over the course
> of a 3 hour race? Because if I can't achieve let's say 95% hull speed or
> more, then all I've done by stretching the boat is to increase the weight
> and wetted surface and to reduce efficiency. And as you can imagine, in a
> multi-sport race where I'm on the go for 15 or 20 hours, efficiency is
> very important.> And before anyone jumps on me by saying that I should forget hard chine
> stitch and glue and immediately gain 3% in speed (that number is from a
> commercial site) well yes, I do realize that. However, since this will be
> my first kayak and I'm just starting out in paddling as well I prefer the
> simple and fast building that Stitch and Glue represents. Once I've
> paddled it for a while then I'll have a better idea about what is
> important in my next boat.> Thanks for any ideas.
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Maximum Effective Kayak Length:
I built a series of 4 experimental flatwater racers that were basically the same design, but of different lengths. My weight was 188 lbs. + 32 lbs. boat weight and a 2 lb.paddle. Total load: 222 lbs. The fastest and sweetest paddling was the first, at 18'4". As I attempted to make them faster by adding length, they only got progressively slower, with the 21'5" one being the slowest of all. I then proceeded to analyze the amount of wetted surface on these different designs and found that it increased greatly beyond the ideal length of 18'8", for my weight. The skin drag on the longer boats was greater and the extra length was a liability, not an advantage. I later designed an unlimited-class flatwater racer at 18'8" and it was faster than my 17' sanctioned boat. The ideal length and waterline beam needs to be changed in regards to the paddler's weight to achieve the fastest speed.
You might wonder why single rowing shells are built at 27', with only an 11" beam. It is because of the shifting weight of the rower during the strokes and the need to have more length to keep the shell from squatting and porpoising around the lateral axis. A rowing shell with sliding oarlocks and footbraces and a stationary seat could be made shorter and faster.
Steve McDonald Eugene, Oregon
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