Repairing Crack in GRP

Forbsie

Forbsie

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Eventually got my boat onto strops this afternoon for 10 days of repairs.

The first major problem is to repair an 8" crack in the hull just behind the 3/4 keel. The crack runs across the keel then back about 4".

Can anyone offer any advice or tips on the best way to proceed. The guy that quoted me to do it professionally hasn't called me back.
 
Hi Gordon
go back to the to the front page click on sailpower.com then Features then minor gel coat repairs
If its deep glass the interior first...good Luck
cheers Joe
brainy barsteward will probably do a link 4 u in a mo
 
Thanks Joe. I'll accept your Good Luck because the crack is all the way through. It only 'wept' as I took it up river to Swan Island though. Sort of the same as I'll do when the final bill comes in. /forums/images/graemlins/crazy.gif
 
GRP does not tend to crack but rather under extreme tension tears apart.
Unlike metals where a fatigue crack right through can slowly grow.
This means that most likely it is a crack in the brittle gel coat.
I presume there is no sign of water getting through or any sign of crack on the inside.
The fix is to grind away the gel coat until there is no sign of the crack. Use a magnifying glass to cloely examine the area. then recoat with epoxy. Epoxy sticks better and does not shrink as much as the original polyester.
You can put a pigment in the epoxy if it is not an area painted with A/F.
Obviously there has been stress on the hull at that point and if you are concerned then you could possibly build up the area with more glass or even layers of Kevlar (for tensile strength) or carbon fibre for stiffness. Either on the inside or outside of the hull.
My guess is that it is only a superficial crack caused perhaps by flexing the hull when running aground or similar. good luck oolewill
 
G'day William.

To give you some background, I'm moored on the tidal Thames. Every year they maintain the lock below me (Richmond) which means that I have to take the mud. This year the keel pushed through the hull due to the weight of the engine. The crack is visible on the inside and it is taking water (although not a lot).

I need to strenghthen that part of the hull and having taken note of your carbon fibre/kevlar comment will discuss this with The Fibreglass Shop tomorrow.
 
Id strengthen the keel on the inside. Where you have the void in the keel moulding Id put in a keel timber to soread loads. Bedded in on epoxy then encapsulated in glass it should last the life of the boat.

One thing to remember is to let the underlying matt dry out. It would have taken up water. Maybe not a lot but a bit.
My plan of action would be to sort the keel then tackle the repair. In one way your lucky that its delow the water line and will be anitfould over so cosmetic finish is not paramount. The art is in the finish.
Grind back the grp around the crack feathering it out. The amount you do this depends on the size of the crack.
Build up matting to in an increasing larger area to cover the crack. Build up slightly higher than the existing then sand back. Finish off with gel coat. Again slightly hiher than the surrounding and sand back then polish.
When we put the engine in, or before, would have been a good time to do the internals.....hindsight huh!
 
G'day Forbsie,

This is a simple repair that most can do for themselves, just a few points to remember are:

Use epoxy resin and cloth designed for epoxy, that means no chopped strand mat (CSM)

Support the weight of the boat so the keel is in it's 'normal position' and under some tension.

Grind a small amount from the outside to reduce the amount of cloth be applied overhead. Grind the inside out till you have a gap along the line the crack was on.
Both sides should be ground at about 12 to 15 degrees so you end up with a feathered edge and taper to nothing at the gap.

On the inside grind off an area at least 150 mm to 300 mm each side of the crack, this will give you enough area to strengthen the hull by tapering the lays of cloth.

Check you have ground out all of the crack, it may extend 100 mm past what you see prior to grinding.

Precut the cloth, start with the largest patch and then reduce the size by about 50 mm to leave a 25 mm space on all sides, you will need at least 6 layers of 256 gram cloth, if you think you need more, say 8, widen the area to be ground out. The idea is to spread the load by making the new glass thinner as it gets to the edge and the original hull thickness.

Use a ribbed roller to roll out excess resin as too much resin will weaken the job, you are looking for a 1 to 1 ratio by weight (Not 3 resin to 1 cloth as with normal resins).

Glassing overhead is best done by wetting out the cloth on a smooth surface first and lifting it into place draped over the back of your hands, protected by latex gloves like the doctor has, (I promise this won't hurt a bit but may be uncomfortable he said).

For a neat finish add a layer of roving's, this also heps cover any exposed ends of glass under it.

Andavagoodweekend....
 
I would also recommend epoxy because it sticks to old grp better than new grp does by a mile. You can get CSM for epoxy - but having tried it I wouldnt recommend it. Epoxy is like treacle so the prob you get is that you pull the CSM to bits with your brush as you laminate, and end up with an epoxy re-inforced hedgehog.

If the load on your keel has pushed it up into the hull (is it e Benny?) you need some srious re-inforcing half bulkheads to spread the load over a much wider area of the hull. I used thickish marine ply, cut to shape from a cardboard template, and then laminated into the hull with epoxy and woven rovings.

Guard against ending up with one very thich re-inforced area suddenly stopping at a sharpish edge and going back to the original laminate. This would be a high stress area - you need to fade the repair into the original.

Should be good fun - but you may well need a lot more than 10 days to do a good job when you dont have all the tools, past experience etc. Epoxy can take a couple of weeks to totally harden out at this time of year
 
Having read your further comments...

I would advise against DIY unless you feel very competent and don't care too much if your insurers decline a claim due to the a failure of this repair, which could easily prove catastrophic when sailing hard on the wind.

It is highly unusual to incur this kind of damage, not least as a result of 'the weight of the engine' when taking to the ground.

More likely the keel has suffered some pounding previously, or she has been grounded at speed, levering the keel backwards and depressing it into the hull at the back.

In either of these scenarios, a workman-like and particularly a seaman-like repair would involve supporting the hull in such a way that the damaged hull is close to it's designed profile, and the glassing in of new / extra floors or stringers within to reinforce the whole area to the rear of the keel. The damaged hull wil require considerable grinding out on the outside and re-laying up in layers back to the original, or perhaps slightly better specification of lay-up. Of only slight consolation, this kind of damage often leaves a depression behind the keel that can take an extra layer or two of lay-up right where you need it. Of slightly less consolation, once the new / repaired floors are done, it sounds like the keel needs to come off if the crack runs through the stub.

I've no idea about the age or value of the boat in question. If it's worth a bundle, get it spec'ed and over-seen by a surveyor who knows. If its an older / cheaper boat, get a yard or GRP man who knows his stuff, and if you like the sound of his suggestions, go with it.

This does not sound like a trivial repair. The sideways forces on a keel have been known to pull one off when enirely up to the specification laid down by the no doubt well intentioned designer. Your sounds well short of that!
 
Re: Repairing Crack in GRP ...

The boat in question I believe is a Motor Boat and not a Fin / long keel sail boat. Therefore keel stresses are more longitudinal and barely transverse as in a full blown sail boat.

The keel in question is probably more of a "spine" than a keel plate and joint.

Therefore repair is possible - but must be ground into, faired and backed up internally to provide stiffening. The addition of transverse stiffeners in form of GRP Rope or timbers may be advised.
 
Re: Repairing Crack in GRP ...

having re-read your post I think andy_wilson is right. best get a surveyor to examine the boat / damage and recommend a repair at least before deciding whether its within your capability or not. but if you do use a yard, then best get a surveyor to oversee the repair.
 
Re: Repairing Crack in GRP ...

Thanks for all your help, guys.

Having now jet-washed off the hull, I've had a better look at the problem. The initial diagnosis of a large wide crack was actually a 3 year old bodge delaminating. Once this was ripped off, the true crack in the grp, while still all the way through, isn't actually as bad as it seemed.

With all the advise from this thread and a visit to The Fibreglass Shop in Brentford, I've equipped myself with enough epoxy and heavy-ish cloth (285gm?) to do the job. I'm going to repair it both sides and probably incorporate some extra strengthening inside. I've printed everything out to study and if my clients stop pestering me, I'll get started on the grinding this afternoon.

Thanks again for all your help and advice.
 
With the best of wishes and success ....

I cannot give advice that subsequently could land me in liability etc.

The posts about surveyors looking are correct and advised - but at end of day they will only recc'd what they consider is best ... without structural dismantling and deep investigation - it will be an opinion.

I don't mean to sound harsh with that ... but stating fact as a Surveyor can only report on waht he observes ... and having been one for a number of years !! I know that well.

The proof of the pudding will be the grinding back and removal of old repair ... similarly I would be inclined tro grind back inside to see colour ! and state of laminate there.

Let's be honest any repair is possible by owner given care, sensible approach and not rushed. The problem here for owner and for a surveyor as well ... is to understand how far the problem lies into the structure.
It may be that the repair has to assume that the structure around the crack is compromised and therefore greater emphasis on strengthening and spreading load out ...

I think we will get an update from Forbsie as the repair progresses and I don't blame him for doing it himself ... I also consider that as he asked for advise, seems to listen and also to investigate - that he will likely do a good job ...
 
Re: Repairing Crack in GRP ...

Have you ever thought of doing a "boatyard" type program of these repairs /forums/images/graemlins/smirk.gif

cheers Joe

Smile,camera,action and....................................???
 
Keith!!! .....

Can we have "Boatyard" added to the swearword dictionary? /forums/images/graemlins/wink.gif
 
The story so far....

I've ground out the crack into a fairly wide "T" section and laid 3 layers of 285gm cloth on each side using West Epoxy. One thing that I've missed in my studies is information regarding this waxy deposit left on top of the epoxy once it has cured (a mate just mentioned this last night in the pub). Because I've used a grinder/softpad and a sander to level and key-up the area, I'm hoping that I'll have taken off most of this wax.

Today I'm going add up to 3 more layers on each side using an ultra-violet heater between each layer. While I've been warming the epoxy pot in a bath of warm water, today I am going to also warm the separate epoxy and hardener prior to mixing as it's 'kin cold out there.

Another problem that posed itself when we took the boat out was a seeping leak out of the bow at the front of the keel. This may have happened during the draw-off or may be due to a block of concrete used as ballast under the floor of the v-berth. Hopefully this will have dried out and I can start grinding it out and repairing it.

I had a visit from BarryH and Seaspray III and it was suggested that I put an "S-shaped" strengthener up the back of the keel and over the top towards the engine. This would then be attached to a glassed-in drip tray which would provide some transverse support. All a bit difficult to explain to you without pictures.

Thanks again for all your help and support.
 
Re: The story so far....

G'day again Forbsie,

The residue left from curing is best removed with running fresh water and a plastic scourer, the little yellow and green blocks with a yellow sponge on one side and a green scouring pad on the other, simply rub the surface till the water no longer forms beads, only takes a minute.

As you have ground and or sanded the area with the residue still on, you have spread it into the work area, a good wash with Acetone will help.

Also, did you measure the thickness the hull in the area of the crack? this information will help determine how many layers you need to bring her back to full strength and how far to extend it to make sure you don't create a hard spot.

Avagoodweekend.
 
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