Hi Pete,

The strength of a piece of wood is not determined by whether it is flat sawn or vertical grained but how the grains are oriented over the length of the piece of wood itself.

Think of a piece of wood as being comprised of tubes - like a bundle of straws held together with glue. If all the fibers are intact, you have maximum strength; as more fibers are cut there are less to support the load and more stress is placed on the weaker glue - the strength is compromised.

The limbs on a wood bow a subjected to extreme tension and compression stresses. It is critical to make sure that the wood grain is not violated. Bow limbs are
typically made by working starting with a single growth ring for reference because this is an easy way to make sure that the rings are intact. Edge ring [vertical grain] bows are just as strong - it just takes a bit more care to do.

This discussion has more bearing on making paddles than kayaks. A paddle is just like a bow - one launches kayaks, the other arrows. Paying attention to the grain pattern on a paddle will allow you to make it stronger for less weight.

Is grain orientation important in strip style construction? Well, yes and no. Yes, [perfect] flat grain would theoretically be stronger - but the second you began to fair the hull you would start cutting the grain fibers. The wood strength is not critical in this type of composite construction because the wood serves primarily as core for the fiberglass. The fiberglass is the grain - it provides the strength.

IMHO, edge grain strips are easier to fair, flat sawn have a prettier grain pattern.

Hope this helps.

Hank