Very unobtrusive when the rod is not in place. Note that the aft end is attached to the hatch, while the forward end is attached to the front of the companionway.

See Hatch

Close up of the end connected to the hatch itself. With it closed all the way, the hatchboards are impossible to remove without an ax!

See The other end

The end attached to the front of the companionway. You can also get wooden holders but they were pretty big and I like how the cheap white plastic blends in!

See Hatch lock aft

Thanks to an ingenious poster on this forum, I installed this super easy, cheap and effective lock for my hatch. It consists of one closet rod and el cheapo closet rod holders. Total cost: under $5 and NOBODY is getting through this!