Designing a wave ski or surf kayak

[cthippo]

I think for my next project I want to build something for playing in the surf. Not a hardcore boat or anything since I only make it to the ocean a few times a year, but something I can get our and play on.

So given that, I'm trying to figure out whether to build a surf kayak that you sit inside or a wave ski that you sit on top of. The only plans I've found are for a surf 'yak by Guillemot, but it's only rated to 180 lbs and I'm 270 before gear.




This is a waveski from Caribbean Waterworks, but it's only rated to 220 lbs




Given that as far as I can tell no one makes a boat in anything like my size, I guess I'm going to have to design and build my own. Isn't that terrible

I'm probably going to use either skin on frame or stitch and glue construction.

The question I'm trying to figure out is how big does it need to be for adequate buoyancy and aside from a flat bottom and upthrust nose, what else are the key design elements?

[girvin]

only use this advice if you promise not to use it around surfers or at local surf spots! Go by a block of 2lb or 3lb eps. Make a hotwire (very easy just google it). Cut the basic shape out of the foam block you can make rocker templates from a existing one. You pin th templates on either side of the block and run the hotwire on the masonite or ply template, Perfect rocker. Use a surform to start rounding out your shape. Switch to 100 grit and a 1x4 piece of wood as the block don't buy one they aren't as good. Round the edges with the block. Start with the sand paper early to get a smooth surface and getting out the rips. If you get it smooth no need to spackle unless you are going to paint the foam under the glass. Then glass the whole thing. Since flex isn't as big a deal as in surfboards I would go with a somewhat heavy layup. Triple 6oz E cloth for the deck and bottom wraping the rails and s cloth patches where you sit. Then fill coat and sand. For these applications I like Resin Research (I have no affiliation), I use it on all my epoxy boards.

This is not the traditional way to build one but will work very well. Also you don't have to buy a mass produced piece of crap from #@$%. If you want one built for you I can do it just PM me I am in your area.

Girvinsurfboards.blogspot.com

[girvin]

BTW you can find out how many ltrs they one for 220lbs is and just upscale that to find out how much more foam you need.

[cthippo]

I love how easy you make it sound

Where would I get the foam in sheets that size?

[girvin]

You can buy blocks of eps at different suppliers contact fiberglass supply they are close to you and can point you in the right direction.

[Poida]

I prefer sit ons than sit ins for surf, I don't like the idea of being inside a kayak as it's rolling over rocks or even sand. I like to depart from my kayak when she rolls.

I have found weight distribution important as you don't want the nose to be waving around losing steering control or the nose to be too far down so it digs into the surf and does a cartwheel.

With a sit in you are stuck in one position even to the point where you can't lay back to change the weight distribution as the wave condition changes.

If you are designing a sit on, it would maybe an idea to have a sliding seat that can lock into several positions.

[Doug Lord]

Originally Posted by cthippo

I love how easy you make it sound

Where would I get the foam in sheets that size?

--------------------
I use EPS for a lot of small part building. I've found that you can get the foam thru architectural foam suppliers and it's cost effective for small stuff.
The two places I've used cut to my specs(square or rectangular)-I shape it from there. They have both had 1, 1.5 and 2lb per cubic foot foam. If you use 1 lb foam you've got to be very careful how you shape it because if you use course paper too close to the finished shape the surface will have a lot of little pits where beads pop out. I've used mostly the 1 lb because my stuff is generally not structural.

[girvin]

You can't use 1 lb. It will require too much glass and you will still get compresion dents. Stick with 2 or 3 (3 is hard to find). I use 1lb only for sandwich construction on very high performance boards. For example On a board I am making for a pro surfer I am using 1lb with 1/42 bamboo veneer vac bagged on each side the hand laminated with 4oz e glass on bottom and 4oz s glass on the deck a 5'11 will come out in sub 5lbs with bamboo fins and stronger than a traditional board built with pu/pe. The sandwich construction Is one of the only ways the 1lb is ok for this type of vessel.

[cthippo]

Right now I think I'm going to go for a sit-inside or maybe a sort of a hybrid design. The reason has to do with water temps around here, and the fact that they never get very warm. It's wetsuits all year round here, and a lot of surfers wear drysuits, even in the summer.

Right now I'm looking at either a scaled up version of the 'yak above or a hybrid design that is built similar to a waveski, but with a cowling or cockpit. A friend of mine has offered me his stash of closed cell foam in thicknesses up to 4" which I hope to use as the core of the hull and then use skin on frame construction for the cowling.

I got an email from Nick Schrade at Guillemot and he said the plans for the surf kayak in the original post can just be slapped on a photocopier and enlarged. The question I have is "how much?". I need a 50% increase over the design capacity but does that mean I need to enlarge all the dimensions by 50%? Seems like there's a cubic function in there somewhere.

[KJL38]

You are correct it is a cube function, so to increase volume by 1.5 you need to multiply all dimensions by 1.145.

Have you seen the experiment with a SOF surf kayak at http://www.capefalconkayak.com/rhino.html

[cthippo]

Originally Posted by KJL38

You are correct it is a cube function, so to increase volume by 1.5 you need to multiply all dimensions by 1.145.

Sorry to be dense, but can you show me the equation for that? What would be the result of a 1.2x increase to make the math simpler?

Originally Posted by KJL38

Have you seen the experiment with a SOF surf kayak at http://www.capefalconkayak.com/rhino.html

Yeah, he's going for something a little different though. OK, well, a lot different.

At one point I had started saving to go build a kayak at Cape Falcon, but life got in the way and I ended up going it on my own. His F1 design looks awesome and I've actually got the drawings for it hanging on my wall. I'm hoping to do down there this summer and take a class from him.

Are you by any chance familiar with the Australis Salamander kayak?

[KJL38]

The math is 1.145 x 1.145 x 1.145 = 1.501

If you used 1.2 then

1.2 x 1.2 x 1.2 = 1.728

I've never paddled a Salamander and only seen them in a shop, are they available in the U.S.A?

[cthippo]

Aha, thanks for educating me!

Sadly, they're not, which is why I asked. They look like awesome boats, but I'd have to import one myself. I've pretty much decided I don't need a large cruising 'yak, but if I could figure out how to get it into the country I'd give the Salamander a look.

[KJL38]

I don't think the Salamanders are anything exceptional or I would see more of them around as they are at the cheaper end of the spectrum here. For plastic sea kayaks in Western Australia I see far more Dagger, Wilderness Systems and Current Designs kayaks which have been imported from the other side of the world.

If you were to import one maybe the Australis Iguana 3 piece would be easier and would offer something not available from your domestic producers but do you need a 3 piece? I had a 3 piece NDK explorer and seldom dismantled it, I bought it because I liked the way it paddled and it was the only one available.

[Milan]

Michael Storer has very basic design, simple and cheap to build in plywood.

http://www.storerboatplans.com/Russki/Russki.html