This is specifically about the Wide "D" Shackle, 3/16" Pin Dia. The pin diameter is important because it's narrow enough that most, if not all, of your keys will fit on the pin without drilling. Then, with your keys on the pin, and the pin screwed home, they'll lay flat in your pocket and not get tangled.
No idea what you'd use it for in the boating world, but if you've got a pocket full of keys, it's darned handy for that.
Bottom Line Yes, I would recommend this to a friend