Stress Cracks

[cammo]

Hi all,

Have just picked up a cheap 14ft fibreglass runabout to have a bit of fun with. Have begun fixing the floor, in order to cut out some soft spots and have come across these cracks on the hull that have me concerned.

What is the best treatment for these and what caused them? A big hit perhaps? The inside looks fine, but should I reinforce from the inside and treat externally?

Thanks in advance.


Jason

[cammo]

Ok, read through a few other posts and went outside to sand away a bit to have a closer look. You can see the following pictures. I don't really know too much about it all, but it appears that the middle section, where I sanded more, the cracks disappeared, moreso than the edges. Would this be right or am I being hopeful?

[marshmat]

The "spider cracks" and "crazing" you see here is probably only in the gelcoat. As gelcoat ages it can get hard and brittle, and it starts to crack near fittings and in high-stress areas. Even the winter freeze-thaw cycle can cause this. If the cracks are only in the surface gelcoat, and do not extend into the laminate itself, your problem is merely cosmetic and is easily resolved with sandpaper and paint. Only if the cracks go deeper into the fibreglass would you have reason to worry.

[michael-compwes]

fiberglass don't like to flex--it breaks down over time,,so I'd think you'll find that the 'soft spots' you refer to will have associated structural cracking/breakdown in the fiberglass.
The cure depends on the situation--do you have access behind the panel?---- is it cored with balsa or foam??

[cammo]

The soft spots were in the floor only and were caused by an unsealed hole letting water into the ply. I have cut these out as per the photo with the square hole and will repair.

The crazing is in the hull, and I dont have access...yet, but another cut in the floor could be arranged if necessary.

If the cracks only just go into the resin, should I re-resin, or just paint. I know this is quite speculative, so appreciate the replies, to a novice like me.

Just worried sanding through gelcoat, and taking some of the strength away.

Cheers

Jason

[lewisboats]

I think Gelcoat and Strength are rather mutually exclusive. Gelcoat is for looks and water permiablility or the prevention thereof. It is brittle and...as you noticed...cracks. The strength of the hull comes from the fibers underneith the smooth coating.

Steve

[michael-compwes]

Originally Posted by cammo

The soft spots were in the floor only and were caused by an unsealed hole letting water into the ply. I have cut these out as per the photo with the square hole and will repair.

The crazing is in the hull, and I dont have access...yet, but another cut in the floor could be arranged if necessary.

If the cracks only just go into the resin, should I re-resin, or just paint. I know this is quite speculative, so appreciate the replies, to a novice like me.

Just worried sanding through gelcoat, and taking some of the strength away.

Cheers

Jason

.......can you ascertain wether the hull cracking is around stringers and 'hard-spots'?-if it's not too extensive,you can get away with some minor re-enforcement,,,or nothing at all.
....gelcoat adds NOTHING for strength,,but in my experience the cracks generally show where the structure below is flexing too much for longevity's sake.

[cammo]

Yes the stres cracks are mainly around the reinforcement ribs, moulded into the hull. Obviously the hard areas, and there is no noticeable strength difference between cracked or non cracked areas.

[marshmat]

Take a good hard look at those cracks one more time. Is there any discolouration or lighter-coloured spots near them? This would indicate the laminates beginning to separate, in which case you'd probably want to cut out the damaged layers and repair the layup. If the cracks only go into the gelcoat and the fibreglass underneath is sound, you're probably OK to just fix the gelcoat.... but I'd agree that some minor reinforcing would be in order to ensure it doesn't happen again.