Hi,
Does anyone know of a website that does a good job of laying out some of the performance differences that result from subtleties of hull design?
I am interested in learning more about how differences in flare, dead rise, etc. effect handling and performance, etc. I am not asking for any particular reason…I am just interested in expanding my knowledge.
thanks
Matt
nope
those are descriptions of parts so a site that described kayak design parts would be kind of like describing plumbing by describing plumbing parts. Check out Nick Schades book, The Strip Built kayak or Mariner website. I don’t think you’ll get what you’re seeking beyond generalities,"rockered kayaks are more maneuverable than straight keeled,except where x,y,z ".
Goodman’s chapter
Frank Goodman’s chapter on design in the 2nd edition of the BCU handbook may provide some of what you seek.
It is not in the 3rd (current) edition.
Some links
Use names and terms from these to search for more:
http://www.oneoceankayaks.com/smhydro/hydro.htm
Most of the usual design/calc terms explained.
http://www.greenval.com/jwinters.html#technical%20articles
The “Speaking Good Boat” and “The Shape of the Canoe” series are must reads - as is anything by John Winters.
http://www.paddlewise.net/topics/boatdesign/pro-conswede.html
That last one is a series of posts on pro/con of swedeform shape between some great designers - and there’s more that can be searched there.
Had more somewhere, but after reading Winters and seeing the terms explained on the One Ocean site you’ll have plenty to search for - and lots more to find (but not much better).
Congratulations Matt
for doing something very rare…Taking the step to learn a bit about hull design and hydrodynamics / statics! I think the more you understand the more you’ll realise how much of the industry is marketing smoke, and the more you will enjoy various boats. Greyaks list is good. Winters is excellent at describing things. Broze Brothers of Mariner kayaks as well. Guillemot is also good. Talk to some R&D designers or shapers too if you can get access.
Getting Technical …
Hard to make a fast boat and have it still be “kayak like” on the pointy ends.
Hard to make a fast boat with “kayak like” pointy ends…
“Kayak like” = what is the assumed-middle-of-the-road-acceptable norm.
Check out Nick’s site, too
He’s got some good technical articles there. I refer people to his stability article frequently.
Ok, the details…
>Hard to make a fast boat and have it still be “kayak like” on the pointy ends.
Hard to make a fast boat with “kayak like” pointy ends…
So Pat,
Does this mean it is hard to make it “kayak like” on the ends for a given length? or that there is something inherently faster about non “kayak like”?
I assume (maybe wrongly) you are talking about plumb vs upswept bow (& stern?). So I’m ignorant about whether plumb bow gives you a longer water line length vs. total length or if there is something else it does.
And what the heck do baidarka square sterns do?..
But if fast was my main interest, I’d get a new body…
"Kayak like"
I don’t know what kayak-like means either.
As far as fast, efficient hull design goes, a good place to look is rowing shell development.
The fastest shells now all have plumb bows and stern decks that taper down into the water line.
The same applies to classes of sailing yachts that leave a lot of flexibility within a certain formula.
Common traits are long waterline and semi-circular lofts.
How about pinched sterns?
My Elaho is concave or nearly so in the stern quarters–sort of pinches in to a longish but narrow tail. I assume that’s intended to make it easier to turn when leaned, but I also suspect that shape of being a significant contributor to the boats desire to broach in following/quartering seas. It feels like the boat would be easier to steer with the hips downwind if it had some convexity there that could be engaged with a lean. Am I on the right track?
John Winters’s book
My understanding is that “The Shape of the Canoe” exists in several versions, and that the latest and most complete can’t be had for free on the web. You have to pay somebody (I think greenval.com) for a DVD. I haven’t compared my DVD to everything that’s on the web, so I don’t know this for certain.
The version on the DVD sure is exhaustive. Most of his writing is about speed, though, and the original poster seemed more interested in dynamic stability. Winters says that much of the talk about stability isn’t based on science; it’s more experience and copying and art and trial-and-error. Here again I’m just passing this along; I don’t know enough to verify it myself.
– Mark
(IMO ) Part of the answer lies in the
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question ..... Track - ing ..... ruddered or not compromise and peoples perceptions of what a boat can or should do....... and then having to sell them to the widest range possible.
Sorry Bowler, Here is some good info on appendages etc.......http://www.ae.uiuc.edu/m-selig/references/naca-cit-031115.html
concave ends
– Last Updated: Jan-30-07 9:36 AM EST –
my $.02 is that the concave end on the Elaho is a design hangover from the Arluks and has very little to do with a desired handling trait. It's easier to turn than it's predecessor because the kayak has more rocker, and not "multichines for more maneuverabiltiy" Also the Elaho started as a shorter waterline kayak.
The Arluks and CD Solstice boats come from a particular time and place where rudders eliminated a lot of design criteria for the hull and the long concave ends were a way to have a long number on the l/w charts without having a lot of added skin resistance. The Arluks have pretty awful down wave performance and the Solstices are very hard to turn. The Elaho was a first evolution away from rudder dependant design.
If you get a chance paddle a QCC kayak, a Gulfstream, an Arluk and a Sostice. The Gulfstream looks like it has the same hollow ends as the long boats but whats touching the water is pretty much all convex/full shape like the QCC canoe body. In 2' choppy waves the long hollow ends(lack of buoyancy) of the Solstice and Arluk ends transmits more torquing movements back to the paddler resulting in more abrupt changes in stability. Upswept ends have utility going through junk and hard landings and as handholds but the severe concavity of the older Neckys and CD boats gets in the way of handling IMHO.
Really?!? I knew that a plumb bow would
be faster under constant speed, but I thought the under-carved bows I learned with were due to some need to control bobbing caused by the intermittent acceleration of the strokes.
Is there a site where I can see some of the plumb bow hulls? Or possibly I will see them if I am in Boston next summer and revisit our “old” boathouse.
What about the wasp-waisted kayak
offered recently? Is the pinched waist to help paddle action in some way, or to help speed and glide?
Siamese rec boat!
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Seriously. If the hull were really wasp waisted the wave making would be more like two short hulls than one long one.
Wasp waist is not really what's going on with the kayaks though...
They claim the "wings" are out of the water mostly - with more typical hull form below in the water - and the "wings" are there for secondary stability/as sponsons only.
Of course, even in small chop that ain't true. They'll alternately engage and add drag.
Above water sponsons aren't needed on flatwater boats (they shouldn't be engaging) - and irregular shapes aren't good on rough water boats (making them pitch and be less controllable and unresponsive to leans).
So, what is this design good for? Who is the target market? Flatwater newbs who want to think they have a fast boat - and yet still have it act like a fat boat as soon as the water textures a little?
If you need more beam - just add more beam - and keep the lines fair. Personally, the more textured it gets the less beam I tend to want, the more I need it to respond to leaning and edging, and the less boat I want to have to work overall.
With kayaks, fine entries and fair lines are hard to debate - as is paddler ability and choosing right tool for the job - but that doesn't seem to stop anyone from trying *L*.
Sponsons?!? Heaven forfend !!
Subtleties
I think that might be the key word in small boat design.
IMO there will always be as much art as engineering in these boats.
Good thread. Some links I hadn’t seen before.
Thanks,
Tommy