Stress cracks in hull gelcoat

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RobBrown

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On recent inspection a series of concentric rings of very fine cracking in the gelcoat on the hullside have appeared. Evidently non-structural, but according to the surveyor, probably caused by some weight locally compressing part of the outside of the hull, generating an area of expanding rings of stress cracks, about 2-3' across, presumably when the deformation pressure released. Probably created some time ago, but becoming more obvious as material penetrated the cracks, oxidised & blackened.

A general wash & hand polish with some Farecla G3, doesn't seem to have had much impact. Any suggestions for a more effective DIY treatment, short of re-gelcoating the area?
 
I'm new here and I think my posts are still being moderated, so this may arrive too late. Sounds like your hull has taken a hard knock. I did once ask a boat builder friend your very same question in the pub one evening, and he basically said - no there isn't any simple way of fixing stress cracks. However, I have a theory that there might be, but I haven't tried it. You could use a dremal with a cone shaped bur on it and cut a V groove in to all the cracks, then fill and fair them with some gelcoat or gelcoat filler. Wet & dry them then polish. Assuming your gelcoat is white and the same shade as the new gel, it may work. If it's another colour or shade you are very unlikely to make an exact match and it could end up looking worse.
 
RobBrown said:
On recent inspection a series of concentric rings of very fine cracking in the gelcoat on the hullside have appeared. Evidently non-structural, but according to the surveyor, probably caused by some weight locally compressing part of the outside of the hull, generating an area of expanding rings of stress cracks, about 2-3' across, presumably when the deformation pressure released. Probably created some time ago, but becoming more obvious as material penetrated the cracks, oxidised & blackened.

A general wash & hand polish with some Farecla G3, doesn't seem to have had much impact. Any suggestions for a more effective DIY treatment, short of re-gelcoating the area?
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2-3 FEET across. Wow, they are pretty big cracks then.
You cant do much remedial work with gelcoat by hand, but if the cracks are that big, I could imagine they are all they way through the gel, so I dont see what polishing will achieve- the cracks will still be there.
If they are very fine, and the gel is now stable, and the boat is of a certain age.. leave them and keep an eye on the area.
Either that, or a few hundred notes, find some one to re-do the area.
 
RobBrown said:
On recent inspection a series of concentric rings of very fine cracking in the gelcoat on the hullside have appeared. Evidently non-structural, but according to the surveyor, probably caused by some weight locally compressing part of the outside of the hull, generating an area of expanding rings of stress cracks, about 2-3' across, presumably when the deformation pressure released. Probably created some time ago, but becoming more obvious as material penetrated the cracks, oxidised & blackened.

A general wash & hand polish with some Farecla G3, doesn't seem to have had much impact. Any suggestions for a more effective DIY treatment, short of re-gelcoating the area?
Click to expand...

We are in the middle of having our gelcoat touched up/repaired/re-done by so called proffesionals. It at last looking really nice. It was all down to Stress Cracks. A surveyor friend told us that ALL boats made of fiberglass and having Gelcoat will eventually get stress cracks.

All the best and good luck

Peter
 
35mm said:
I'm new here and I think my posts are still being moderated, so this may arrive too late. Sounds like your hull has taken a hard knock. I did once ask a boat builder friend your very same question in the pub one evening, and he basically said - no there isn't any simple way of fixing stress cracks. However, I have a theory that there might be, but I haven't tried it. You could use a dremal with a cone shaped bur on it and cut a V groove in to all the cracks, then fill and fair them with some gelcoat or gelcoat filler. Wet & dry them then polish. Assuming your gelcoat is white and the same shade as the new gel, it may work. If it's another colour or shade you are very unlikely to make an exact match and it could end up looking worse.
Click to expand...

This is what I did a few years ago. Boat was built in the early 70's and had numerous star cracks in the gelcoat. Just ground them out as described, down to the laminate (which appeared undamaged) then filled and sanded smooth.
I then overpainted the whole underhull with epoxy primer. been looking good ever since...
 
When my boat had some repairs done where a yacht had hit the stern a couple of years ago, the repairs were finished off with flowcoat to match the existing surrounding gelcoat of the cockpit, and very nice too. However, recently there have been a couple of places that are now showing stress crack lines that were not evident as part of the repair at the time.
I haven't tried filling them yet but was considering using flowcoat to at least cover the most visible ones. I now remember there is Captain Currie's Crack Filler sold in the chandleries in small tubes, so may give that a go if white in colour.

ianat182
 
ianat182 said:
Yes you'er right again VicS! Is it the jacknife that was the Currie's(curry's !!?

ianta182
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Yes. Captain Currey. I have one somewhere.

lockspike_bosun.jpg
 
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I would also take a good long look inside and outside the effected area to check the integrity of hull/laminate and that it's watertight. Cracks like that could show a weakened hull and is also how osmosis can start if the water can get in between gel and laminate. Make sure you drive any water out before sealing!
 
Thanks for the replies on possible remedies. I have previously used dremmel and small quantities of gel coat on small individual gel coat cracks, but these particular marks are very differnt to the usual stress cracks. They are very fine indeed and numerous and quite long. If you can imagine ripples in water radiating from a point source, with the first foot or so from the centre being completely clear and then partial rings radiating out around that area for another foot or so, but very incomplete circles. Because of their individual very fine indistinct nature, they are clearly not canditates for individual treatment and do not look deep enought to warrant drilling out in any event.

As said the boat was subject to a professional survey and the verdict was- not structural and unlikely to be any significant laminate involvement- tho it could of course not be ruled out by a simple visual inspection. I was wondering whether a wet & dry regime of some sort or of any intermediate chemical abrasives might be worth trying &/or if there was any generic inexpensive coating product that might be available to try as a DIY if only to hold matters for a year or two until I can fund a professional solution.
 
In that case it sounds like it's just an old hull with age marks? In which case I think any remedy you try will have a similar effect to using Oil Of Ulay on an elderly face - it will cost you money and not have any noticeable effect! My boat is very early 70's and is covered in them, but they are surface only and really mostly cosmetic. It would cost a lot to fix so I see mine as simply adding character! :)
 
I read some place that some new hulls are being machined/baked/laser built and so stress cracks appear in the Gel Coat sometimes because they are so perfectly made.

I am not sure if this was bru-ha-ha but just read/heard it some place.
 
Jamesuk said:
I read some place that some new hulls are being machined/baked/laser built and so stress cracks appear in the Gel Coat sometimes because they are so perfectly made.

I am not sure if this was bru-ha-ha but just read/heard it some place.
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Sounds like an after sales excuse to me. I'de be pretty P***ed off if I bought a new boat that was all cracked up.

This thread does remind me of a story about a chap I know who was sent to a boat yard and told to find "Ocean Queen", and instructed that it was booked in for a new gelcoat. He turned up at boat yard, found the boat called "Ocean Queen" which was only about 3 months old, and set about with his grinder removing all the gelcoat. Two days into the job, he was told he had gone to the wrong boat yard and removed the gelcoat from the wrong "Ocean Queen". Expensive mistake. True story!
 
Yes oldish boat- 1983 and plenty of wear & tear marks, like the owner, but these particular ones are now more noticeable on the white gel coat due to darkening, location & overall size. I am generally phlegmatic, but a bit difficult to be quite so with these now. The repair manual link from VicS, does have some comments about hairline fractures, which apart from the concentric nature, look very much like mine, with filled resin & wet & dry regimes so I might try that very cautiously to see it is of any help.

Can any one clarify exactly what a "filled resin" is and how this differs from gelcoat, whether it needs to be specific to a 1980s Moody and any sources? Not asking much am I?:)
 
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My understanding of gelcoat cracks is that they can either be cause by an impact, a high stess, or a failure of the gelcoat. High stress usually occurs around bits of boat with high loads imposed on them (like chain plate attachments or winch mountings), or where the loads are low but the layoup is thin and there's flexure, or where there are sharp internal corners that locally raise stresses (like some window or hatch apertures). The impact ones are caused by impacts, obviously, and they characteristically radiate out in a "spider's web" centres more or less round the centre of the point of impact. This sounds like the latter case.

I believe that they're caused because the gelcoat resin is far more brittle than the rest of the laminate (a) because of the pigment and (b) because it has no fibres in it. As a result, the laminate flexes, but the gelcoat doesn't, and cracks. I'm told it's worse on boats than fibreglass cars because boats tend to be "self-coloured" (rather than painted) and have thicker gelcoats than cars to keep the water out and provide a good depth of colour for the hull.

With damage like that, the recommended way is to reinforce the BACK of the laminate locally with a layer or two of glass mat and resin, then grind out the affected area of gelcoat and replace it (with more gelcoat). Attempts to just fil lthe cracks in the gelcoat don't always work because the laminate behind it (if the cause was an impact in the first place) will be less stiff and the new gelcoat, (being brittle) won't be able to flex with it.

Unfortunately, depending on how old the boat is and the quality of pigment used in its original construction, getting an invisible match might be tricky because the new gelcoat won't necessarily fade at the same rate as the old stuff did.
 
Interesting that you say the cracks do not look that deep.
Are you sure they are not scratches?
Cracks in the gel coat will always go to the full depth and meet the fibreglass.

Do the cracks have 'crows feet', branch off at angles?

Do they resemble a spiders web with a specific centre.
Crushing cracks usually are running in parallel

Cracks are:
Very narrow
Full depth of gel coat
Sharp edges
Branch off and have crows feet
Do not crisscross

They could be a collection of curved tramlines, due to crushing pressure, but as I say, very unusual to see them in a concentric fashion.

We need some pictures please.
 
I think "filled resin" is a variation on what sometimes gets called "flowcoat" - it's like gelcoat, but thicker, filled with some sort of bulking agent and pigment. It gets used as a thick "paint" to make sure the "hairy" ends of the glass fibres in the laminate are covered on the inside. It also contains a bit of wax so that it doesn't dry tacky. Gelcoat doesn't contain the wax (because the air is excluded by the mould on one side and the laminate on the other), so it dries hard and non-tacky anyway. It may or may not be pigmented (but usually is on boats).
 
Marine Reflections said:
Interesting that you say the cracks do not look that deep.
Are you sure they are not scratches?
Cracks in the gel coat will always go to the full depth and meet the fibreglass.
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I've come across cracks that don't go all the way through to the laminate. I agree that stress or impact ones do, but Avocet's gelcoat failed (especially in areas subject to UV light) and those cracks didn't go the full depth. Some did, but many only went part way through - as I found out when I started grinding it all off!
 
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