: If you wanted to build a very light (35 pounds or less) strip kayak for
: fairly gentle recreational lake use, how would you go about it? 1/4"
: thick strips, 4 oz glass on the outside, even lighter on the inside?

I'd first look for a design that was fairly short and wide, with a fairly broad entry angle. A needle-like point would not be desirable.

I'd build with narrow and thin strips, preferably 1/2 inch wide and 1/8th inch thick if I could get them. if not, then I 'd look at 3/16th strips and maybe plane them down a bit more. With such thin strips I don't know if there would be any advantage to using bead and cove edges. The reason for using thin strips is to save on weight. The reason to use narrow strips is to keep the angle between strips as small as possible so that I don't take off a lot more wood when I sand off the ridges formed by the seams as I fair the hull.

A single layer of 4 ounce cloth inside and out. I'd only consider adding a second layer to the bottom of the hull if I got a lot of damage over a period of years, otherwise I'd just patch any minor scrape and ding damage as it occurs. Your biggest weight gain is going to come from excess resin. The thinner you apply it the lighter the boat. Thin cloth means a thinner film of resin is needed to hide the weave.

You might check into getting some 2 ounce cloth. Using two layers of 2 ounce cloth instead of one layer of 4 ounce would allow you to get the same strength (which is mostly a matter of how much glass is there)but because the lighter weight fabrics are sheerer you need less resin to fill their weaves. Since you'll use almost twice the length, compared to 4 ounce cloth, you might even qualify for a discount, and get a better deal on the lighter fabric. Oh, and the thinner and lighter fabric should be nice for repairs as it should feather in easily.

There is also the possibility of using 1/8th inch plywood (3mm) and constructing the boat in a lapstrake fashion, with wider "strips" (maybe 3 inches wide) overlapping each other by about 1/2 inch. This gives you areas of the hull which would be 1/4 inch thick (at the overlaps). This thickness adds to the strength. between these thicker areas are roughly 2 1/2 inch wide areas which are 1/8th inch thick. With this thick/thin construction you get the benefits of both the thicker matreials for strength, and the thinner materials for lighter weight. If you use marine plywood you will not need to use glass cloth over the entire boat. Generally these boats simply reinforce the bottom of the hull (the "football" area with glass cloth, and seal the wood with a couple of coats of epoxy resin, so you save the weight (and cost) of the glass for sheathing the entire boat. You save 2 pounds for every quart of resin that you don't use. Look for the book by Thomas Hill on Ultralight Boat Building.

here is a link to the first page of his chapter on plywood lapstrake construction.

http://www.amazon.com/exec/obidos/tg/detail/-/0071567038/ref=lib_dp_TFCV/002-5271394-9936042?v=glance&s=books&vi=reader#reader-link

The book itself is available on amazon.com at this link:

http://www.amazon.com/exec/obidos/tg/detail/-/0071567038/qid=1057117484/sr=1-1/ref=sr_1_1/002-5271394-9936042?v=glance&s=books

You might also consider saving weight (and time and cost) by not making a wood deck. You could make a fabric deck from a lightweight fabric sealed with the same urethane varnish you apply over your fiberglassed hull. Your cockpit coaming would be wood, and you would need a few deck beams to support the fabric. A very lightweight cover would be suitable for only limited rolling, but you can gain a relatively big weight reduction. Even so, this would be more than enough for the sheltered waters you are considering paddling. The disadvantage is that you give up easily-sealed compartments. You would then want to use some sealed bags for flotation. Of course you cna remove these before hoisting the kayak on your car, so that may be an advantage.

Finally, if your desire to have a lighter boat stems from difficulty in getting the boat on top of your car, why not get a trailer (easier to et the kayak on) or look at one of the devices used for loading (much heavier) rowboats onto cartops. There are various lifts, slings,hoists, jacks, and levers that will assist.

PGJ