Hi Ben

The one in the photo is 45mm back from the tip and 15mm down from the deck. Do run some epoxy round the inside of the hole or put a tube in as others have done, if only to keep water out of the foam (if there is any foam in that part of your boat).

If you are using 4mm rope then a 4mm hole is all you need.

I use a 15mm washer on the outside to spread the load but it depends what is under the skin. If it's foam then it can be deformed by the pressure of the knot. If it's glass or filler the washer wouldn't be necessary.