Rowing boat repair layup

Hi,
I have a 12ft fibreglass? rowing boat with a 12" x 5" hole where the trailer side support burst through.
I've grinded out the damage, but I can't actually see a fiberglass layer, all I'm seeing is Gelcoat? The hull is only about 5mm thick.
How should I approach this repair?

 

Can you post a photo or two please of what it looks like now after you applied your grinder to it?

If the hull thickness is 5 mm, then that could perhaps be three layers of chopped strand mat sandwiched with 2 layers of woven roving.

One way of fixing it would be attach a panel over the hole on the outside to form a mould surface, after first grinding a long bevel all around on the inside of the hole, and then lay up layers of fibreglass mat and roving from the inside, overlapping on to the hull.

There are many ways to skin the proverbial cat (similarly for fibreglass repairs), and I am sure that you will receive some more opinions soon.

 

Thank you, I'll take a close up photo tomorrow in daylight, it looks like a super thin bit of glass on the inside, and the rest being Gelcoat.

 

You can put a couple of strips of plywood from outside with drywall screws to make a mold. Put some plastic in between to keep the wood from sticking. Lay mat to the same thickness as before. Paint or gelcoat can be used for the finish.

 

Thank you, I've got polyester resin and 300gsm CSM, is that suitable?

 

Yes. It should be fine. If you are using resing without wax, cover it with plastic so it cures properly.

 

I think for that hull shape you will need 2 pieces of quite flexible plywood.One needs to be a good fit to the lower "plank" surface and one needs to be an equally good fit to the upper plank surface.Any gap along the edge of the upper plank line can be filled with modelling clay or similar.If you can find melamine faced plywood you will automatically have a pretty good finish to work with.I would use a gelcoat that overlaps maybe 3/16" onto the existing gelcoat and then 3 plies of 600gsm mat to make up the laminate.I would make the final piece of mat large enough to overlap the edges of the ground away portion by a couple of inches or so.You may have to do a little blending of the edges of the gelcoat on the outside once laminating is concluded if appearance is important to you.

 

Perfect, thank you all very much I have a game plan now.
I've done non critical repairs previously, but not below water and so I was a bit concerned about it failing on the water, to the extent that I considered scrapping the boat.