Hull repair.

i like CDK`s idea.... from the outside, grind the hole so that there is a tapered edge to the hole, say at least 45degrees..... 30 degrees even better. Make it neat as you can, a router with a bearing bevel cutter would be ideal.

On a flat benchtop (melamine, formica etc), apply mold release, then apply gel coat that matches the colour of your hull, then many layers of glass with polyester or vinylester resin to build up the thickness of the hull. Then release the peice from the table and cut the plug out with a hole saw or jigsaw etc.... match the bevel tapered edge using the same router bit so the tapered plug finishes flush with the hull. Glue the plug in with pigmented resin and you will barely notice anything was there from brand new.

Patching a small hole doesnt need to be a massive structural ordeal, only has to keep the water out (resist hydrostatic pressure), so glassing patches both sides isnt nessesary IMHO and is overkill in this situation.

The above would be a very neat way of doing it. However, simply mixing up some resin with silica and milled fibres to make a thick bog, then filling the hole and tidying it up afterwards with flowcoat etc would be quick and easy... you could do it in 2 fills if the hole is too big and the bog sags...

 

A technique used in repairing plasterboard might help with some of the methods suggested above.

Bevel the hole but make it oval, cut a piece of ply just wide enough to pass through the widest part of the hole and make its length greater. Drill two holes in the ply and pass a wire through them.

'Post' the ply through the hole, turn it around and pull against the inside of the hull. If you put a stick across the outside of the hole and twist the wire round it, the ply should stay in place. You need to be careful the board is bigger than the inside bevel.

You should be able to put a bevel on the inside from the outside which if the repair is all one piece it will stop it falling in or out.

Did the sea cock give any structural support to the hull? If not anything you do will be stronger than it has been in the past.

Health warning, I have never repaired a hole in a fibreglass boat.

 

Yes, there are many ways to get it done, some people get locked into a mind set of "this is the only way it will work", but in reality you have several options.

 

On inside prep with acetone and light hand sand. Stick with polyester, a 1/4" <day-old polyester fibreglass plate on. cure hours later, taper hole on outside (keeps dust out), lay-up out outside with cloth, finally gel-coat! Gel-coat the plate on the table when being made.

Minimal effort and dust!

IMHO

 

Ok-- Fit a 16 grit on a drill arbour backwards so that the disc is facing the drill. pass the arbor through the hole from the inside and fit in the drill. Grind down the inside by rotating the arbor till half the hull thickness is gone making a dish shape on the inside.

( less grinding and slower, those 4 inch kick up dust and make a mess. Could also use a vacuum inside while girnding)


Slap a 6 layer of glass in the hole. After dry the outside would grind out and into the internal repair. Again 6 layers of wetted out glass slapped into the hole and roll out. Glass more if necessary.

No gell coat as it antifouled.

Hows that?