Ensure the wood is dry, get a tight fit and then launch the ship. Give it a week or so and wood will swell and the metal bits might as well be welded onto the wood.

For extra fun maybe wrap a rope around it. Looking at the bits that are left over I’m not sure it’s much of a mystery. Wouldn’t be 100% certain but those 4 open bits seem to be the mortises for the wood to fit in.

Edit: saw other pictures below, looks like there’s a mortise in the other side, same deal just my 4 open bits comment is wrong.