How you test and what you consider "failure" is dependant on what you plan to do with the results. A builder of a flat-water racer is interested in different things than a steep-creek hair-boater. The flat water racer is mostly concerned with distributed loads and getting away with the lightest boat that will hold together with the weight of the paddler in the boat going through waves. He will not be too worried about impacts with hard objects because he will presumably avoid hitting such things.

The hair-boater needs to worry about surviving severe impacts with hard, sharp objects.

Because of this, the flatwater guy may be more interested with how a large panel responds to distributed load. The hair-boater may be more interested in what happens with a sharp point load on a smaller panel.

What constitutes a failure depends somewhat on attitude. Is a dimple in the outer surface a failure if it doesn't let water into the core? Since it probably weakens the boat for the next time it is stressed, yes it is a failure. Can you continue to paddle the boat even when there are signs of stress? Yes, so maybe it is not really a failure.

It is useful to note where the test panel responds to forces and how it responds. The point of first damage and final catastophic failure may show up quite differently for different test panels. One panel might show signs of damage early yet hold together long after another panel which damaged late. Some panels will look fine until right before they fail, others will accumulated damage slowly.

What is acceptable may depend on whether you will be paddling someplace "safe" or someplace remote and "dangerous".

You should try to decide what you plan to do and try to match your test to most closely simulate what you perceive as the threat. It will not be practical to test for every eventuality. If you think you will be hitting things hard, whack your panels with a hammer. If you will be playing in big surf, try bending your panels.

> I've been toying around with the idea of building some test panels of 3
> & 4mm plywood with various fiberglass lay-ups, then subjecting them to
> destructive tests. I know that this has been done before, as referenced in
> Nick's book, but was thinking of testing out the multiple-thin-cloth-layer
> theory along with standard lay-ups. I have a few questions I'd like to
> throw out there:

> 1) Would I be gaining new knowledge, or would I be wasting my time by
> re-inventing the wheel? If there are any internet links to the test that
> was already done, I'd appreciate a post...

> 2) What would be the best test to perform? I was thinking of using
> 12" square panels, supported (but not clamped) on 2 edges, with an
> increasing load placed on a board running down the center. (a 3-point
> bending load)

> 3) What would constitute a panel's failure? Audible crack? Revealing of
> cloth weave due to stress? Wood broken through?

> I'm busy building an Outer Island, so I don't have a lot of extra time at
> the moment, but would like to attempt some tests this winter...

> Thanx, Dean