600, inside the hull, lots of rotten wood

a lot of people get carried away with how difficult they think cutting a big hole in a boat and repairing it is. Best thing to do is just not be shy, but make sure you tilt the jig-saw blade the correct way or you will have issues.

I'm guessing that when you spoke to LDC that advice will have come from miller, and i would trust what he says to do. When you replace the blocks of wood, it is a good idea to paint them in resin, therefore sealing them from any water which may get into the boat and preventing any rotting.

personally, i would just cut a big hole out so i could get in there, get rid of all the dead wood and replace it all, then do the hole repair.

cut out your shape, easiest shape is a circle in my opinion. you need to tilt the blade so that when you have cut the shape out you can sit it back over the whole. (from the top of the blade to the bottom, the blade points towards the centre of the whole).Its best to draw a circle first and then make some marks on it so you know which orientation if fits back on.

Then do your repair work in the inside of the hull.

And to attach the cut out shape back, mix up a thick epoxy bog mix (bubbles, silica, microfibres), and apply a good amount to the edges of the shape, and the hole. Then position the shape into the hole and push down gently so the mix oozes out, trying all the time to get the shape in the exact correct place so it is fair with the hull. Let this mix go off fully.Use a long straight edge to assist with this.

Then you will need to grind the gel-coat and a small bit of laminate away around the join, you need to be carefull you dont go into the core. Probably looking at a 40mm with of ground back area all the way around the join. You will then need to put 2 layers of glass over the area(only wet out the bits in the ground off area though!!), make sure this is consolidated well, and then peel ply over the top, if you have the facilities then vac this stage down.

When that has gone off you need to sand the laminate so it is nice and fair and slightly below the height of the rest of the hull. Once you are happy with the shaping, it is the gelling stage. Providing all the previous stages went well the gel should be pretty easy. Apply the gel to the ground back circle (may need a couple of layers), and finish off by sanding through the grades and polishing.

Hope this helped

You could cut the hole and do the repair yourself to keep the cost down but then get LDC to do an invisible repair