: Sorry this is basic, I'm building my 1st canoe. From what I have gathered
: they provide rigidity. When a strip of wood is bent it wants to straighten
: out. Is this outward force the critical function?

: I'm debating on using strips of bamboo laminated at 1"-2" by
: .25" by 2-5' for ribs. They provide a good amount of outward pressure
: and are FREE.
: Or buying some oak, hickory, ash, or something.
: Or puting kligicell/divinicell foam core for deck and re-infocing sides with
: more glass.

: Another thought, Do I even need ribs or deck re-inforcement? Can I get by w/
: all glass with out being too heavy?

If you use enough glass and resin you can forget about ribs. There are many glass boats on the market which do not have ribs. It doesn;t matter whether they were born in molds, or developed freehand -- if the wall thickness is great enough the fiberglass alone will be strong enough to work without ribs.

Typically, to get a thick enough fiberglass part for the hull you'll see manufacturers using about 60 to 80 pounds of glass and resin for a 16 to 17 foot canoe. If the resin/glass ratio is about 50 percent glass and 50 percent resin by weight (again a typical combination), then you would have about 30 to 40 pounds of resin -- or about 4 to 5 gallons. The other part would be 30 to 40 pounds of glass cloth. If you use a 9 ounce glass cloth (that would be 9 ounces per square yard) then it would weigh just under pound (15 ounces) for a running yard of fabric in a 60 inch width. Therefore, you would want 30 to 40 yards of this fabric, which would be good for building up a hull that was 6 to 10 layers of fabric thick. A lot of less expensive fiberglass boats use a sandwich made of layer of glass mat set between two layers of cloth. this reduces the cost of the glass, and the mat soaks up the resin like a sponge. You get a cheaper, but heavier boat with less glass and more resin.

Or, you could install ribs.

with ribs supporting a flexible fabric all you need is a membrane on the outside that is strong enough to not leak. Water pressure on the skin is something under 1/2 pound per square inch ( typically) so the waterproofing materials don't need to be very thick or strong. A film of paint works. But all those square inches of fabric, and all the pressure on them, adds up. If you load your 50 pound canoe with 250 pounds of gear and paddler you'll displace 300 pounds of water -- and that means 150 pounds of water on each side of your boat pushing in towards the center, trying to close the boat up around you, liks a giant clam grabbing its dinner. If your boat's ribs can withstand 10 pounds of pressure without cracking -- and most ribs may deform, but they can do this easily -- then you would want to install 30 to 40 ribs along the length of the boat. Thats if you just used ribs for support. Actually, the thwarts and the seats press out on the gunwales and resist a lot of the compressing force of the water that the boat displaces. The ribs, then, carry a much smaller load -- but you'll notice that they run from gunwale to gunwale, and as they are squeezed they transfer some of the pressure to those gunwales.

Bamboo should make nice ribs. Bamboo was used for years for fine fishing rods, and it bends about the same as fiberglass fishing rods do (very generally speaking, that is) so I would expect you could find a thickness of bamboo which would hae the desired combination of stiffness and flexibility to use in making ribs. Boiled or steamed bamboo can be bent easily into the desired rib shapes, too.

If you bend and weave your bamboo into oval hoops they will be stronger than individual ribs, and if you connect these hoops with straight bamboo pieces running longitudinally, or the length of the boat, you can cover this with a fabric skin -- or even a blue poly tarp -- and have a boat quickly and cheaply. Pictures of this process, using willow shoots instead of bamboo, can be found at http://www.shelter-systems.com/kayak.html

There is a picture of this below.

Hope this helps

PGJ