Stress cracks in hull gelcoat

I know what you mean, but i'm positive that it's only on a 'crazed', lower resilient gel coat.

Concentric cracks although rare, would suggest that this is an isolated area that is affected, rather than the failure of the gel.

I could be wrong of course - heaven forbid :D
 
Marine Reflections said:
I know what you mean, but i'm positive that it's only on a 'crazed', lower resilient gel coat.

Concentric cracks although rare, would suggest that this is an isolated area that is affected, rather than the failure of the gel.

I could be wrong of course - heaven forbid :D
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No, I agree that this one probably IS damage rather than gelcoat failure. I used to work with fibreglass cars and saw the "concentric / spider web" thing many times after parking knocks, and this does sound very like one of those.
 
Marine Reflections said:
Tiny thread drift (sorry OP)

Avocet, what happened did you have to grind off the whole gel coat, and re-apply a new one?
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Yes, it's odd really. I never managed to find anyone who had seen a failure quite like it (including on other Cutlass 27s and MARCON builds of the same era). The hull was while pigmented gelcoat. The deck is grey pigmented. Although faded, the deck is fine, but the whole of the topsides were covered in a maze of tiny cracks that looked like impact damage but (a) were completely random in pattern and (b) not even I am so bad at berthing that I could have hit it in that many places! The only common factor seemed to be that the cracks were worse on the higher areas of the topsides, that got more UV. As you went closer to the waterline (and under the stern counter), they got fewer.

I ended up using a router to rip off a "trench" parallel to the waterline, down to the laminate. I'd then fill it in with epoxy and microballoons, and then sand it back flush and do another one next to it (and so on). The venerable Oldsaltoz kindly provided advice and inspiration throughout the process.

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Wow!
That looks like a serious amount of hard work!

I have only seen one with this effect before, apparently it is due to being exposed to a very harsh winter.
My thoughts at the time were that it must also be a lower resilience in the gel coat and surely not just the weather, with the cold just being a catalyst?
 
Marine Reflections said:
Wow!
That looks like a serious amount of hard work!

I have only seen one with this effect before, apparently it is due to being exposed to a very harsh winter.
My thoughts at the time were that it must also be a lower resilience in the gel coat and surely not just the weather, with the cold just being a catalyst?
Click to expand...
I have seen similar patterned and extent of gelcoat cracking before, on GRP-moulded-galley-sinks on old Westerlys, but also on the decks/coachroofs of a couple of older US-built and imported from Florida boats. Looks like a hot/cold temperature thing - gelcoat not expanding and contracting at the same rate as the underlying laminate.
 
Looking @ Avocets piccies & suddenly starting to get a bit twitchy:eek:

Sorry dont have a photo @ present, but going down to boat @ the w/e so will try to post something then for info, but the general siz eof the cracks, not dissimilar to Avocet, but as said, ltd to one area and a distinct circular, tho incomplete, formation pattern.

Thanks for the addl info on filled resin. I think I might just try a basic gelcoat mix for any first attempt at filling and I recall some recent info on Moody Owners website re type/sources, so will look more on there. Thanks for the assitance everyone. I'll post further idc to up-date anyone who might be interested.
 
Marine Reflections said:
Wow!
That looks like a serious amount of hard work!

I have only seen one with this effect before, apparently it is due to being exposed to a very harsh winter.
My thoughts at the time were that it must also be a lower resilience in the gel coat and surely not just the weather, with the cold just being a catalyst?
Click to expand...

Yeah, it was an awful amount of hard work. It's still ongoing, in fact! I took the boat out of the water in 2006 and it's STILL not back in! It's currently primed, and I was REALLY hoping to get it painted this summer, but we just haven't had a summer! Literally, I don't think I've seen 48 consecutive hours with no rain, humidity below 75% and temperatures betwen 10 and 20 degrees this year! Many's the time I've thought of chainsawing the damned thing up and weighing-in the ton-and-a-half of lead that's supposed to be in the keel!
 
RobBrown said:
Looking @ Avocets piccies & suddenly starting to get a bit twitchy:eek:

Sorry dont have a photo @ present, but going down to boat @ the w/e so will try to post something then for info, but the general siz eof the cracks, not dissimilar to Avocet, but as said, ltd to one area and a distinct circular, tho incomplete, formation pattern.

Thanks for the addl info on filled resin. I think I might just try a basic gelcoat mix for any first attempt at filling and I recall some recent info on Moody Owners website re type/sources, so will look more on there. Thanks for the assitance everyone. I'll post further idc to up-date anyone who might be interested.
Click to expand...

Do try and stick some photos in. It sounds much more like impact or stress damage though. Do any of the pictures on this site help?

http://blog.dankim.com/2010/09/03/gelcoat-cracks/

The first one looks like mine. Old age? Possibly, the boat is 40 this year! Also the gelcoat thickness was indeed quite high (half a millimetre on average) and not particularly uniform, so that might have been it. Doesn't explain why other boats of the same type and age (even kept in sunnier climes) haven't suffered though. I reckon it was probably just a duff batch of gelcoat - or maybe one where the mould was waxed and gelled and then left for too long (say over Christmas) before the laminate was applied.

Note that I'm not sure I agree with the author of the site on some of the others. I think the small "spider" crack (No. 3) is imact damage from the INSIDE of the laminate (someone dropping something hard / heavy (like an anchor or outboard) on to the INSIDE of the hull. The outer skin then gets put into tension and you get the cracks radiating out from the centre of the impact (note there is absolutely no localised damage at the centre of the crack - supposedly the point of impact). I think the following picture is damage from an extrnal impact (localised damage visible), and the outer surface put into compression giving rise to the circular concentric (ish) rings.
 
@Avocet

Yes - eg 2 looks pretty close and his explanation is akin to mine in the original post- compression (inwards) of a localised part of the hull and spring back after the pressure is released, causing the stress cracks,leaving the centre relatively untouched. However pic to follow @w/e.
 
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