Kayak Design Parameters

Builder's Forum
1

Hi...I've been hunting thru the forum to try and find some info on what design factors control the basic characteristics of a kayak but it all seems rather contradictory. The Chesapeake 14, for instance, with a beam of only 21 inches,  is rated as fairly stable, whereas the Shearwater 14 ( beam 23 )inches is rated as fairly tippy, and a couple of anecdotal comments seem to confirm this. My other problem is that at 62 kg ( sorry, 136 lbs ! ) and    5'4" , I don't have enough weight to get most kayaks floating at their design waterline. My current paddle is an Australis Gecko small sea kayak....in still water it sits so high in the water ( due to rocker ?? ) that even with the rudder down it's a constant job to keep it tracking straight. Also I have to hold the paddle uncomfortable high to clear the coaming and dip the blade sufficiently.

At this point I am thinking of trying a Chesapeake 14, but would really appreciate some expert input before I commit....

2

Robbo,

That's max beam - the widest point. It doesn't say anything about the fineness or cross-sectional shape of the boat.

Fineness is a measure of how soon a boat gets wide and how long it stays wide when you're moving from front to back. All other things being equal, a finer boat has less rolling stability.

The cross-sectional shapeis also very important. All other things being equal, flatter bottoms are initially more stable but get less stable the more they heel (lean over). V-bottom boats start out less stable, but the more they heel, the more stable they get. The speed of the transition between stable and unstable also depends on whether the cross section is rounded or chined (hard corners).

So comparing the Shearwater 14 to the Chesapeake 14, we see that the SW14 is finer than the CH14. It comes to a sharp point at both ends and narrows faster in the rear than the CH14. The CH14 also gets wider in the front sooner than the SW14.

The result of all this is that the CH14 has a greater average beam than the SW14. All other things being equal, it'll be more stable. Unfortunately, the line drawings don't show the cross sections so it's impossible to analyze that from the public data.

As far asnot weighing enough to get the boat down to the designed water line, it's the simplest thing in the world to add ballast. Just make it removeable so you can still easily carry the boat.

Have  fun,

Laszlo

PS - Does anyone else find this sentence from the SW ad copy odd?

"Like all Chesapeake Light Craft kayak kits, the decks are smoothly cambered, not cut up into a faceted, homebuilt appearance"

I mean, by definition all these boats have a homebuilt appearance. That's CLC's business - boats built at home. Also, the tumblehome panels are in fact curved facets. Very nice looking curved facets that give the boat a sculptural look, but facets just the same.

Sigh, Here I am grading ad copy writing. Can you guys tell that I really don't want to go out to the shop and sand my dinghy?

 

 

 

3

Another thing to consider is the location of your center of gravity (CG) relative to the small craft you are in.  At your weight, your CG is closer to the waterline than a 200 pounder. So if you both go out in the same kayak (at different times, of course), the yak will feel more unstable to the 200-lber than to you, given that you both have about the same skill level.  The closer your CG is to the CG of the empty kayak, the better the roll resistance will be.  Some people will carve their foam seats so their posterior is a 1/4 inch from the hull instead of an inch or two to gain that little extra bit of stability.  Because there is not as big a market for smaller kayaks there are fewer designs for the smaller paddler.  And designers are leery of offering a small kayak (light load) because people tend to abuse the designed weight limits (e.g., putting their 60-lb daughter in a yak with a lower limit of 120 lbs, or a 250-lb man using a yak with a 180-lb upper weight limit because the yak fits his truck).  You really should try to demo any kayak you’re interested in.  Failing that, look at pictures of small yaks being paddled by children or small adults and check out the waterlines (check that the hulls aren’t rolling to one side or the other).  Also look at how the paddlers are handling their paddles.  Lightening storm coming so have to end.  Any of the small CLC yaks are great, if they fit you and your paddling wants.  Not the last resort would be to talk to John Harris (CLC) or one of the other noted designers and discuss your concerns; they all want you to be happy with what you’re paddling.  Good luck!

4

We are currently building two Sharwater 16s for my daughters.  We have had one of them on the water.  You would fall between them weight and height wise. They both find the Shearwater stable.  However, if I get in the 16, I am upside down in a matter of no time.  (I am fine in a Shearwater 17)

 Jon T

5

Thanks for all the comments guys.....nothing's ever as simple as you hope it would be!!!  I've been browsing thru the photos and videos on the web site  and making notes on various yaks.  ( It's also been interesting to put a face to the names..Laszlo,  looks like you're  the Wood Duck expert !! )

Jon T, I was interested in your comments on the Shearwaters. I had discounted them as having less stability than I would like, but from what you say this might be less of a problem for small paddlers with a lower CG.  Also like the tumblehome on the sheerline to give better paddle clearance.
Thanks again

Robbo

6

Robbo,

I'm just the guy who built one, types a lot and isn't shy about getting photographed (no matter how ridiculous the image - see the wet re-entry). Eric Schade is the expert.

One thing to notice about Jon's comment -the 16 is tipper for him than the 17, even though the 17 is 1 inch narrower. Longer boats are more stable than short ones, when all other things are equal (or close to it). This just shows how the different parameters interact. That's why boat design and selection are a matter of trade-offs between the different factors that each person finds important.

Have fun finding the right boat,

Laszlo