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Tasar Intro>Tasars with Kevlar

In response to a question on the TasarSailor list, Frank Bethwaite provided the following information about the use of Kevlar in the hulls of early Tasars.

The very first Tasar hull to be laid up in the first mould was a kevlar outer laminate with epoxy resin. I watched. It lasted about 40 minutes and when the epoxy did not gel as polyester resin gels the technical manager said "That's enough", the soggy mess was pulled out, the mould cleaned and re waxed, and all subsequent Tasars have been of polyester resin.

At that time kevlar was the all-singing, all-dancing new fibre and was deemed superior to glass in all respects

Opinion about epoxy was even more extreme, and its properties less known. Some thought it to possess evil properties. There were those who "Didn't want epoxy in the place"

The kevlar epoxy structure envisaged by Ian Bruce would have been superb, with strong hulls weighing about 90 pounds. Because epoxy does not shrink, strong woven cloth can be laid against the mould, and the weave does not "print through". This is how we make 49ers and 59er now.

Polyester shrinks; weave prints through; so a layer of low-strength chopped strand mat is laid on first to suppress the weave print through. Then the strong woven cloth is added. The end result is a much heavier structure.

I do not know how many boats were laid up with kevlar. The first change was to abandon the woven kevlar outer laminate because the weave pattern "printed through" the polyester resin. So early boats were a CSM glass laminate plus a woven kevlat cloth, then the foam, then a heavy kevlar woven layer inside

As the properties of the then-new kevlar became better known, it was realised that glass, kevlar (and carbon, then dimly on the horizon) all have about the same ultimate strength, glass stretches 5% before it snaps, kevlar 2% and carbon about 1.25%. but a practical disadvantage of kevlar is that in compression the stiffer glass is superior. Early Tasars driven hard tended to fail internally along the inner carlins; I suspct this may have been a symptom of kevlar failure in compression.

My guess is that the shift back to the better understood glass would have occerred at different times in Montreal and Banbury, and would have been simply substitution of kevlar by glass as stocks of kevlar ran out. It is probable that some hundreds contain kevlar,

All my (Australian) boats, starting with 750 in Jan '77 were glass-polyester..

So bit by bit the original kevlar-epoxy concept became in practice the heavier glass-polyester structure which has served us well..

I have no way of knowing which is which other than to remove a core and disect it - which I have never done..

Frank

Posted 2006-06-02

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