Fiberglass gell crazing

gavin · 14 April 2003, 23:08

This is a problem not unique to ribs, it is hard to find a boat without some gelcoat crazing, does anybody have any experience of a craze developing into a crack,I have seen 5 foot long crazes , fine lines in gelcoat, it is probably normal, however annoying as it is visible on the gel finish of a boat.Does anyone have tips on how to stop crazing taking place, is it accelerated by constant pounding or by flexing of hulls, decks or a combination of each.Does shifting weight cause crazing or does exposure to ultravoilet encourage crazes to form.

jwalker · 14 April 2003, 23:25

Flexing causes crazing.
Polyester resin is brittle. The gel coat has no reinforcement. If the layup flexes to the point where the gel can't follow, it cracks.

JW.

Cookee · 15 April 2003, 08:10

To my knowledge the only way of preventing crazing is at the design and manufacture stage.
We use a specially mixed gel and resin for the race boats and we don't get crazing at all - even after racing for up to 1.5 hours repeatedly in up to force 6 conditions!
All of this of course means more expense but you take your pick!

Keith Hart · 15 April 2003, 08:40

Quote:

All of this of course means more expense but you take your pick

See thread on the cost of building ribs!

Keith Hart

Jonny Fuller · 15 April 2003, 08:48

It's simple, build the boat properly! that cures the problem before it happens, every time.

gavin · 15 April 2003, 21:09

Unfortunally its not that simple, in my opinion flexing is part of the design of a boat, if it didnt flex it would surley be worse, I have seen brand names like Tornado or Antaraes with crazing and in the case of the Benetau Antares cracking I think the idea of a flexible or more flexible gel finish would help like car paint for instance gavin

Cookee · 16 April 2003, 08:43

Gavin - Our raceboat has no bulkheads at all, just a couple of longitudinal stiffeners and when we hit a big one from a great hight I can feel the air being pushed out of the boat as it is flexed. We still have no crazing at all! As John says make it right - correct design and materials.

Jonny Fuller · 16 April 2003, 10:57

Take a walk around the race pits, with the exception of OCR where the weight is so very important to be competitive, and consiquently they are built ( as my dear friend Steve Baker puts it) "marginally" and have a definate 'lifespan'. Any boat that's been racing for at least a season or two, competitively(anyone can keep a boat together by going slow), and has no cracks anywhere to be seen, has had some serious thought and quality construction go into it.
When you work around racing boats, and get to see, or experience what they have to go through, and see the 'witness marks' left when certain parts of the boats flex so much that they touch and it seems imposible when it's sat on the trailer, you soon realise offshore racing (obviously when it's rough) has to be the most punishing test there is! It's only when that chequered flag depends on you gritting your teeth and probably doin stuff you would never do in a pleasure situation that this level of punishment is administered to your boat, constantly, for possibly 100 miles at a time, every race you enter. So it's a bloody good test of structural integrity.

Julian · 16 April 2003, 11:13

Afternoon All

I have had crack on 2 boats , one was a humber which had serious cracks all the way along the tube flange and a dell qauy dorry had cracks all over the place, I have to say that the 3 scorpions that we have owned have never had a single crack or mark on the hull. As you say its show the build quality, obviously i dont race the boat but it has been well used over the last 3 years.

Julian