Thoughts on Building a Light Weight KayakIn general the idea is to reduce the use of resin to the absolute minimum because it is heavy and not very structural.
- Use a seal coat and scrape it off while wet.
- Use satin weave cloths. They have less air space and surface texture to fill with resin.
- Be absolutely ruthless about not letting resin pool.
- Thoroughly squeegee the cloth after wet-out to make sure the glass is not floating on top of excess resin.
- Do not use an end pour. Carve a wooden block instead to fit into that space. If you want more strength in that area, use more glass, not thickened epoxy.
- Avoid thick glass tape for sealing the sheer line. Cut bias strips of your regular cloth instead.
- Keep your filets small, as in very small.
- Make tight fitting joints between strips so there won't be gaps to soak up resin.
- Do not use staples, or if you do, putty the holes before applying resin. Staple holes expose end grain which soaks up extra resin. Furthermore, resin sometimes drools and runs on the inside surfaces which usually does not get removed from the soft cedar because it is hard to do.
- Use pressure whenever possible to squeeze resin out of the glass. For example, tightly tape plastic over the shear-line tape and massage any excess resin to the side. This makes a nice smooth, glass rich structure.
- Use 3/16 inch cedar. This alone should save about 5 pounds.
- Not all cedar boards have the same density. Pick out the lighter ones (although weight differences can be due to moisture that will evaporate later) at the lumber yard.
- Avoid using heavier wood than Western Red Cedar. For example, Alaska Yellow Cedar weighs about 30% more.
- For a coaming I'm guessing that a carbon fiber lip will be lighter than more typical wood types. The heaviest are the stacked plywood types.
- Use carbon fiber hatch lips
- Use carbon fiber tube bow and stern toggles
- Use carbon fiber fittings and cheek plates
- Avoid metal parts like screws and bolts. Individually they are insignificant, but taken as a whole they can add up to quite a bit.
I think a 17 foot boat target weight of close to 30 lbs. is attainable. My last kayak is a full size touring kayak nearly 18 feet long and weighs 34 pounds. It has 6 ounce cloth inside and out and this weight includes all outfitting like seat, deck lines, bungees, hatches, bulkheads, and footbraces.
There are skin on frame designs that are even lighter yet. However my interest is in boats where I'm comfortable making significant open water crossings. SOF boats can be perfectly capable, but boats of this type built for my activities aren't necessarily lighter.