: My partner and I are preparing to build 17ft fiberglass sea kyaks. We were
: told that one layer of 17oz double bias stich mat with vinylester resin
: would be strong enough. We used some to erinforce cross bracing on the
: mold and noticed that it is only 1/16 inch thick. Is this thick enough to
: not oilcan in the hull?

If that is all your hull is going to consist of then you might be looking at problems. However, bracing, in one forma or another can certainly stiffen and reinforce this basic skin.

Look at the design ideas of skin on frame kayaks. The skins are considerably thinner than what you are proposing. If you wanted to, you could use the resing coated glas as a super strong skin over a frame. Or, you could look at where the frams is in reation to the shape of the hull, and add glass and resin to reinforce and stiffen your hull in these areas.

For example, along the interior keel line in a skin on frame you generally have a strip. This may be called a keel strip or sometimes I've seen it called a keelson. You can use an actual wood strip for this part and epoxy it to your hull, or, you can make a structural channel from more glass and resin. One way I've seen for doing this is to set a tube about the size of a garden hose (you can even use a section of actual garden hose) in the area to be reinforced. This is covered with glass cloth and resin, which, when it hardens, becomes an extremely strong structural component. Some people use cardboard or paper tubes for the forms and leave them inside. Some are succesful with greasing the outside of the garden hose and pulling it out after the resin sets up -- which sounds like a chore to me.

You don't have to use a round cross section for these supports. You can use rectangular or triangular crossections, too. You also don;t have to form them in the boat. You can esily make sections of channels for you bracking. Coat a 2 or 3 inch wide and 5 foot long ( or longer) piece of your glass fabric with resin and let it sit, draped over a block of wood covered with wax paper. When the resin gels you can trim this neatly while it is still soft, and set it aside to harden. This channel can then be held in position with a few tiny drops of hotmelt glue, and joined to the interior of the hull with a fillet made from thickened epoxy, the same as a fillet is used to join panels in stitch and glue construction.

Bulkheads provide additional bracing and support to the hull. These do not need to be solid, but if they are then they can provide you with sealed areas for additional flotation. Put an inspection port in if you go this route. You can make these from plywood or wood scraps, or assemble them from fiberglass channels that you manufacture yourself, as described above.

"Ribs" can be made the same way to keep the sides from caving in, or oil canning.

hope this helps.

PGJ