An even lower tech way to steam bend is to wrap your wood in rags and pour hot water over it. The rags hold the heat in very well. I would not recomend this method for all of the ribs on a kayak, but I used it to bend the external keel on my Putz. For ribs check out the sources previously mentioned.

One other thing to remember, certain woods steam bend better than others. Ash is supposed to be the best, yellow cedar is good, mahogany is bad. My ratio with mahogany is 50%, but I only tried it twice. The 3/8" x 7/8" piece broke at a 4" radius. I recommend soaking you wood for several days befor steam bending, this gets the moisture content up in the wood, so it behaves more like green wood.

Mike