Invisible Gunwale (Outwale) Finger/Hook Holds
OK for a start these are not really invisible and I have seen gunwales with rebates (or rabbets) under them for finger/hook holds specified elsewhere. However given the boat I was working on had curved sides the tension would come out of the rope if the hooks slipped towards the end. If you have a boat where the sides are parallel you can just rip your rebate the whole length.
First off cut your rebates in the under side of the piece of wood you are going to attach to your boat closest to where it will be attached. I used a cove bit on my router but all you really need to do is make something that will be a small hole under the outwhale once it is bunged on. Just make sure they are in the same position on both sides of the boat.
Now I made some wood hooks to fit these holes precisely because my ratchet strap hooks hung too far over the top of the gunwales to be stable once I hooked them on.
First off work out how big the hooks need to be and mark them out.
Cut the hook out. Part of the problem with wood is that it has a grain and it can split more easily along the grain than across it As a result the wooden hook needs to be reinforced across the grain. Luckily fibreglass strands abound in my workroom and picking a few inches off the end of the fibreglass ribbon provided a fibreglass thread that was quite long as the thread zigzags across the ribbon and unravels reasonably easily.
I used five minute epoxy and was on my way before I knew it. Just remember to slip the hook as far along the hole as it will go towards the end before you tie it off or the limiting of the size of the holes will have been in vain.