Advice on hole repair in GRP Hull

K

kgwanchos

Member
Joined
26 Aug 2006
Messages
36
Location
Redruth Cornwall
Visit site
Hi all
can seem to find anything along these lines in the search suprisingly so here goes. Got a hole punched in hull just above waterline on Trident 24 as results of swing mooring contact with boat next to mine. When cut out and chamfered etc will be 5 inch diameter. Will be able to build it up from inside so Ive got my resin and mat and assume I will need to stick something on the outside and start layering from within. What I cant seem to get a straight ansa on is do I start with a layer of gelcoat of some description first ?? some say do and some dont ... ANY advice on the business of repairing this kind of hole would be much appreciated....

many thanks

Karlos
 
I wouldnt start with the gel.
The gel is only going to be a few mm thick, so make the repair keeping (or sanding back) the repair below the "surface". Gel afterwards.
If you spray the gel with black paint, when you rub back down, any remaining paint displays any voids or hollows that you have.
 
Hi Karlos,
If you can work from the inside then fix a polished surface to cover the hole and start with the gel coat. After all, that's how it was originally built.
 
Unless you can take a mould of exactly the shape you need from an adjacent area it will be virtually impossible to lay up a perfect finish from the inside. You will be best to lay up the glass onto whatever you use as a support, then fair up using resin and filler from the outside, then gel coat on top of that. The gel coat will need to be flow coat, i.e. with some wax added, to ensure a non-sticky finish. You will almost certainly need to progressively abrade with wet and dry papers to get a perfect finish, then finally polish.
 
best to have filled & fared first then take a mould of the outside with a good overlap.
when you lay-up the mat make a template of the hole on light card.
then mark around the circumference in diminishing rings ( like anual rings in a tree ), each ring approx 3m/m less each time.
lay the template onto the mat & cut the mat largest nxt ring carry on untill no more cuts can be made.
after gelcoat is appliede wetout the smallest piece you have & place onto the gelcoat keep goung untill you have uesd the largest piece .
doing the job this way you dont get strands of mat sticking out & it leaves no grinding to do.
then mat over the repair & surrounding area.
remove the mould & it should be as new

ps make sure you use a ribbed roller to remove air as you lay the mat up

best of luck
 
Quite a good, informative piece. Perhaps it's just me, but I have never managed to get the repair to match as precisely as that with the undamaged hull. Always finished up trying to fair with gelcoat, hence I always put the gelcoat on from outside now.
 
G'day Viv,

Your dead right, getting the gelcoat the right shape can be problem with some profiles and with some material used to try and get that perfect shape.

The whole thing is very disheartening because you know that the new gelcoat will age at a different rate than the original coat, the result is a lighter patch down the track.

You can reduce this by sanding off some of the original gelcoat from the damaged area and using this material in the sew gelcoat mix, the bit of age it has means it will fade at the same or similar rate as the original coat.

You can also reduce the size of the outer hole by repairing the inside first, then grind the outside after the inner layer has cured, this reduces the amount of gelcoat required. But means the gelcoat is added after the repair has completed.

Making a mould is a lot of extra time and material, the end results may not be much better than screwing a sheet of suitable backing material to the hull.

I would prefer to do a repair that is 'close to the waterline' with an epoxy resin to improve the water ingress resistance and add some extra strength, this would mean spreading the material a little further inside to avoid creating a hard spot.

Avagoodweekend......
 
A hole is best repaired where you have a shamfer on the existing skin so that the new layers of cloth are laid in steps onto the skin.
Better still is if you can do the same from the outside such that you get a good chemical bond of the layers laid from the inside to those laid from the outside. A chemical bond is achieved even after the layers have gone fairly hard but soon after hardening.
This means that you use something like a sandbag covered in plastic cling wrap hung from the outside or supported in some way to cover the hole.
Lay up the inner layers from the inside onto this support. When it is hard enough to be self supporting you lay up the outer layers onto the inner layers.
This gives 2 patches stuck together one on each side and bigger than the hole so they can't detach even with no adhesion to the old skin. Which of course there will be.
Finally you use a gel coat after fairing off the outer layers.

It might be a good time to consider repainting the hull. olewill
 
You must log in or register to reply here.

Share this page

Top