Re: 3 MM hull?

Posted by BobE on Mar 1, 2005

The following plus 6 bits$ might win you a cup of coffee at your local café:

I’ve read about experienced strip builders using 2-3mm strips, probably very dependent on the wood used. Never seen one in person. Normally they start with strips in the 4 to 6mm thickness, I think.

You don’t mention planned hull construction/shape. I have 3 different single-seat 3mm hull shapes: tortured - a Severn, hard chined - 17LT, and multi-chined – WR18. However, a tortured design is probably not what you have planned and the 17 uses 4mm bottom panels that are around 10” max width. The WR18 was built using 5’X10” 3mm purchased in Fla. eliminating the scarf on the foredeck and the second scarf in the hull panels. BTW, number one panels on the 18 are less than 7” max.

I’m neither a designer nor engineer, but I think two of the primary concerns with thinner woods are hull flex and puncture resistance. So far I’ve not had a problem with either on my protected, flat-water lake with, at worst, boat wakes or wind driven chop and river rock or old stumps. When verifying seat placement for the WR18, I paddled the glassed hull in the water before any deck installation. There were no flex problems even with my overweight 6’1” 235lb bulk, but remember - I was in a protected flat-water cove. After the decks were installed, my brother Dave, (yes John H. “one of the other brothers Darrell” - and Kyle, you know him from using your Moby latches on his WR18), is of similar height though perhaps heavier. He paddled both my 17LT and WR18 as fast/hard as possible without experiencing any flex. None of these yaks has seen the surf, at least not yet – perhaps this summer. They were built primarily for recreation and exercise on local lakes, rivers, and swamps.

As for weight, my experience is that you can save a lot. My WR18 is 29-30% under published design weight. It uses the same glass schedule as the kit WR18 except that I added lightweight glass on the underside of the aft deck before installing. Other weight savers include: triangular, as opposed to square, cross section sheer clamps (a forum tip – maybe LeeG?) out of spruce and a nailess deck install (external forms). Weight additions were sacrificial bow & stern strips of cotton flock thickened resin similar to the Artic Hawk and the mini bulkheads have large lightening holes, but were not removed. Neither was the deck beam, though I’ve considered grinding it out and glassing the underside of the deck in the cockpit area. Instead, I took the easy way out and made a slope from aircraft foam and micro balloons to shed water over the beam when draining water.

These kayaks have been fun experiments so I’m in the camp that says go for it – at least with one of ‘em. Designers at CLC and others have additional specifications that lead them to rely on 4mm. But hey, if your 3mm boat turns out to have too much flex you can probably fix it with glass or glass/foam sandwich ribs strategically located.

P.S. pay close attention to the outer ply on the 3mm you select. I think it is more difficult for the plywood companies to get the thickness of the outer layers on 3mm correct. One side may be thicker than the other. The thinner ply may not allow for much sanding. Some 3mm BS1088 uses clear glue that doesn’t show as badly should you sand through the top layer. Use a light hand when sanding because the 3mm will telegraph structural components more easily than 4mm.

In Response to: Re: 3 MM hull? by Kyle T on Mar 1, 2005