Hi All,

I agree that finding a finite test is an almost impossible search. As with all good design it has to be a compromise based on sound data.

George Roberts seems to equate stiffnes with strength and this is invalid. All composite structures that use a core be it wood, foam, nomex, aluminium honeycomb can be equated to an 'I 'beam. Thus for a thicker core all things being equal a stiffer structure. However the ultimate strength may even be less.

When one is constructing in a controlled environment then the overall Kayak can be engineered to show varying properties at differing places but when a Kayak set of plans is offered for construction by the general public then I beleive one slided to the side of safety and perhaps a bit of overkill.

I have been doing some tests over the past weeks as I indicated in a previous post. The results so far have been predictable. I must admit that I had a poor batch of epoxy that has effected the results.

The overall indications are that using a 4mm ply core and changing the number of layers of glass on the two sides as well as the weight of glass the stiffnes increases slightly with the increase in overall thickness. Ultimate strength is a function of the total matrix irrespective of the number of layers. In fact if the glass is consolidated correctly then the number of layers has almost no affect on the final matrix.

This does not help the poor person trying to coat his or her kayak with one , two, or three layers of glass. As consolidating this properly without vacume pumps etc. is almost impossible then the number of layers may well have an influence on the overall strength of the hull.

Wow,

Regards

Rob