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labr@
13th Apr 2013, 09:47 AM
Iíve been building a skin on frame kayak over the last few months and while itís not all timber the frame is relevant to this forum. The design is Jeff Hortonís Curlew, 15 feet long, built from the offsets and other information in his book.

The construction method is to make frames from plywood and lash the stringers to these using artificial sinew. Stringer timber is paulownia and was cut and scarfed into the lengths needed. Ply is ĹĒ hardwood marine.

The coaming was made first as it can be stored easily enough while the rest comes together. It was laminated around a melamine faced MDF form. The timber is mainly from recycled timber blinds Ė probably basswood Ė but the lip is western red cedar. It was coated in epoxy as both the timber types are very soft.

First layer on form.
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Finished coaming
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The frame was built on 4 supporting frames mounted on a strongback. Lashing takes some time but is not hard.

Frame lashed on strongback.

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The frame in front of the cockpit rubs against the calves so the bottom was cut out and another half frame was installed under where my knees will go. This also shortens the floorboards so there is not much change in weight.

Photo showsw the new half frame in place before cutting out the bottom of the forward frame.

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This is the completed frame outside for testing paddler fitment and accessory placement.

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It took a long while to get to the skinning but that was started over the Easter weekend. I pulled a few holes in the fabric but the seams are fairly straight and overall Iím pleased with it.

This is part way through sewing the rear deck seam.
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Then it was time to do the ironing - of the skin that is. This shrinks the skin taut and it looks much better after this. There are still some ripples around the coaming but itís acceptable to me.

Interior facing forward.
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Last night the first coat of paint was applied. This is just an oil based exterior enamel. I used something similar on a Sabre dinghy once and it stood up remarkably well. I was tempted to use a clear urethane but my biggest concern is with abrasion so the enamel it is.

After painting I just need to fit the painters and a seat then it will be time for a paddle.

Sumbloak
13th Apr 2013, 09:56 AM
Cool. Got a few questions.

What did you use to skin the boat, and where did you get the material?

What size did you use for the stringers? Since paulownia isn't that strong, I assume they would have to be larger in section than something like cedar or oregon.

labr@
13th Apr 2013, 12:51 PM
The skin is 7oz polyester bought from Jeff Horton's Kudzu Craft web site in the US. Unfortunately he has just found that he can't get any more of this particular material but nylon is available from him and also from others. Polyester is not as puncture resistant as nylon but it does not relax when wet (which induces wrinkles) and takes a wide variety of finishes whereas nylon only takes a few. The Skinboats web site has some nylons and good finishes to match but I'm sure other polyesters are out there somewhere.

I did make the stringers slightly larger than the plans call for but only because it was too difficult (ie I was too lazy) to cut them down to 5/8" from the 20mm thickness of the planks I bought. Would have been quite confident with the original sizes as paulownia is significantly lighter than WRC but not that much different in strength.

Edit: Latest on the polyester is that Jeff has just received stock of a new source and is about to do some trials to work out the best way to use it. After that it will be available in his online store.

Sumbloak
13th Apr 2013, 05:06 PM
Ok. I was toying with the idea of doing an SOF boat at one stage, and looked around a fair bit to see if suitable fabric was available over here. Wasn't really keen on ordering it from the US.

Personally I ruled out nylon because of the slackening when wet problem.

elver
13th Apr 2013, 09:48 PM
I've built a few skin boats. The nylon and goop option is good. Well skinned boats do not slacken to wrinkles. The key is good stitching after pre-tightening the nylon.

The is not however, a source of Australian 'grey' nylon that I know of. ( we've done a pretty big search...). Plenty of per shrunk and dyed stuff, but nothing straight from the mill.

Tom

anewhouse
14th Apr 2013, 08:36 PM
Ok. I was toying with the idea of doing an SOF boat at one stage, and looked around a fair bit to see if suitable fabric was available over here. Wasn't really keen on ordering it from the US.

Personally I ruled out nylon because of the slackening when wet problem.

The nylon on my SOF doesn't go slack. Probably getting it nice and tight in the first place helps.

I bought my nylon and polyurethane from Spirit Line Skin Boats in the USA. I followed their instructions about how to sew the skin and it worked well.