: I question whether this is as big a problem as it is sometimes made out to
: be. A hard impact on the outside of the boat should not transmit to a
: single point, rather be spread out along the plane of the bulkhead.

: An impact of force sufficient to create a problem with the area adajcent to
: the bulkhead would likely penetrate the outer skin of the boat had the
: bulkhead not been there - a larger problem.

: Has anybody actually experienced failures due to stress risers, or is this a
: "paper problem"?

: I'd be more concerned about the sealant failure were one to use foam
: bulkheads.

I agree about the foam, and I think the stress riser problem is real, only within some range of forces applied to the hull.

Let's say for egsample that a wave brings you down onto a rock. The force is applied to the hull just in front of the aft bulkhead. This force can be of such magnitude as to:

A) Not fracture or breach the hull

B) Fracture but not breach the hull

C) Fracture and Breach the hull

If the hull is allowed to flex as with a foam bulkhead, then the magnitude of the force required to do any one of the above will be greater than that force required to do the same with a stress riser.

If the force is just barely large enough to do (B) with the stress riser, then without the stress riser it most likely would have done (A)

If the force is just barely large enough to do (C) with the stress riser, then without the stress riser it most likely would have done (B)

A force which is large enough to place it well within the (C) catagory would most likely brake the hull with or without the stress riser, however, the damage may still be greater with the stress riser since the force now has a fulcrum at the bulkhead which will cause a break at the bulkhead and another break where the rock is applying the force.

How much difference there is between the force required to (B) or (C) is dependant on other construction variables, but I don't think it is usually a large difference. I think the chance of the forces falling between (B) and (C) are kinda small.

I think Shawn's solution to spread the stress over a larger surface area is a good one. You could substitute a "reinforced hull around the bulkheads" in the above egsample for the "without a stress riser" situation, and replace "no reinforcement" for the "with a stress riser" situation. The magnitude of the forces changed but the egsample is still valid.

Well I hope I'm not the only one who knows what I'm trying to say here!

Anyway, I think kayaking usually relieves stress no matter what kind of bulkheads you have and I'm a go'in to get my yak on the water with or without stressses!

Doug