We got the above hole in 69667 - Bold Forester at the 2013 UK National Championships. This is how I fixed it.
I made a template from thin cardboard which is a little bigger than the damaged area. In my case I used an old computer punched card. I currently use rectangular patches with rounded corners to prevent fatigue cracks starting at the corners in a situation like this, so made the template that shape. However it's not possible (in my experience) to make such patches invisible. To do that you need to hide the two edges which are running across the grain direction under something (like a shroud block, or the butt strap). If that's not possible, then an oval patch with sharp ends gives you the best chance of making it invisible. For more details see Guitar Repair by Irving Sloane ISBISBN-10: 0860011577 ISBN-13: 978-0860011576.
In this case my intention was to have the top edge of the patch a few mm inside the gap between the inner and outer gunwale.
I removed the varnish around the patch using 80 grit wet & dry sandpaper used dry, so that in the next step I would be cutting wood fibres, not the varnish. It also helps match plywood colour (if you are trying to do this) and means the pencil would leave a visible line. I drew around the patch with a sharp 2B pencil.
I put a steel rule outside the damaged area so the pencil line is just visible and then I used a marking knife to make the two cuts into the top ply laminate across the grain. Use ideally a scratch awl (if you have one, or something similar) to make the cut along the grain and around the corners. Having the rule outside the damaged area means the beveled edge of the cut from the marking knife is on the damaged area side of the cut.
Now cut the damaged area out cutting a bit inside the line with a coping saw or similar .
