: I am not
: disregarding weight here, but I really don't see a big weight penalty
: using thicker strips.

If you went from 3/16th to 3/8ths you would double the weight of the wood component of the boat. If you used 22 pounds of wood with 3/16th strips, then the 3/8th strips would give you an unsheathed boat that weighed 44 pounds. Assuming you added 16 pounds of fiberglas to either, you'ld have either a 38 pound boat or a 60 pound boat. The 60 pound figure is pretty close to the weight of a commercial fiberglass boat, so it is not an unworkable combination, but I think that working with 3/8th inch strips is overkill.

"Strength" is a concept that many people seem to chase after. I'm not sure why. For the hull itself, the "strength" of the materials which make up the hull is mostly irrelevant. A straight-sided, diamond-shaped "kayak" about 16 feet long and 2 feet wide (there aren't any designs like this, but I'm just grabbing at a simple shape to keep the math simple) would have a "footprint" of about 16 square feet. Put a 320 pound load in that and you have a load of 20 pounds over every square foot. When the boat is in the water, the water pressure on each square inch of the hull is less that 1/7th of a pound. That is an incredibly small load, so the "strength" of the hull materials can be very, very low.

For a very long time people have made extemely durable kayaks which had the hulls covered with flexible, and not very "strong", fabrics and hides.

The deck, which is not subjected to water pressure most of the time, can be even weaker.

Building a boat with strips that are 1/16th of an ich thick, or thinner, would work fine. Thick paper, and thin cloth have been used with success.

All of the above makes perfect sense if the boat has a frame.

With stitch and glue construction you have frames (of a sort) which are made from fiberglass which is cast in place during the construction. Most people call these "frames" by the term "fillets". If you oculd build a S&G kayak and dissolve away the plywood you could see the fiberglass frame which remained. Each fiberglas component would be in the location of a "chine". The plywood covered the spaces between these, and provided a replacement for the ribs to support those chines.

Boats which do not have frames need to be engineered in such a way that they can develop and maintain their structural strength. A monocoque hull, such as those built of cedar strips, derives it's strength from the complex sharing of loads around the curves and bends and through the fiberglass skin which rides on both sides of the wooden core. In these designs care should be taken that the kayak has some structural integrity.

If you had an "exceptional" design and constructed it from strips of veneer a few thousandths of an inch thick, the boat might perform wonderfully in tank tests, only ot fail dramatically when a heavy paddler placed a foot in the cockpit and the boat folded up on him, like a giant clam grabbing a diver in some old movie. That same design, built with the same thin strips, might carry a 500 pound load, or more, if it has reinforcement in the proper areas. Such reinforcement would not need to be very great, or very heavy. It would need to be in the right place, though.

: In the same grain what is the opinion of using multiple layers of
: epoxy/fiberglass for strength versus thicker strips.

Pound for pound you get more strength from fiberglass skin than from the wood. The big problem with solid fiberglass boats is that the fill the area between the strong skins with heavy fiberglass materials which are basically heavy place holders. It is like the difference between a solid bar of iron and an "I" beam. The "I" beam has the unnecessary extra weight removed.

With greater separation between the layers of fiberglass, that is, by using thicker strips, you get greater strength. But you already have more strength than you need. When you go with thinner strips you get an added benefit, which is flexibility. When the boat hits an object, rather than breaking, it deforms, or flexes, and then springs back. In many cases this would be a better attribute for a boat hull.

This is an evolving area of kayak design and construction. No one has a final answer on how thin is too thin, or how thick is too thick. What we have are general histories of what has worked in the past, and we build our designs from them. Experimentation has shown that some of these earlier designs can be tweeked, using thinner strips, or thicker glass, or thinner glass.

Something which has surprised me over the last few years is the strength of decks which have been pieced together from little more than chips and pieces. While the general rule for hull strength has been to use long strips, or to stagger the joints so that no two adjoin, these "rules" are simply ignored with some of the fancy and beautiful designs that are being made. A checkerboard design, with all the small pieces, and lined up joints, should (according to old thinking) have nearly no structural strength at all. Yet, people who build decks ( and coamings) with designs constructed from numerous small pieces seem to have absolutely no problems. Go figure.

My best guess is that most of the kayak designs out there are already over-engineed when built with 1/4 inch strips, and that extra bit saves the day for newbie builders and eccentric designers as well. If you stay with 1/4 inch cedar strips you'll be in the area of extra caution. If you want to go lighter, then 3/16 th strips, and even 1/8th inch strips have been shown to be successful. Of course with stronger hardwoods, like oak or ash, thinner strips could be just as strong as 1/4 inch cedar.

The glass fibers give the strength, the epoxy holds them in place so they can do their job. The more glass you put on the stronger you'll have things. Because we use extra coats of epoxy resin to fill the weave of the fiberglass we use more than we need to get the maximum strength from the material. Working with a fabric which has a very flat weave -- either a very thin material, or a material woven of very fine yarns -- would allow for the maximum amount of glass mixed into the resin, and still give a smooth finish.

Just some of my thoughts on the matter.

Hope this helps

PGJ