Thought 1: Are you sure the noise is a rat? If you have much bottom
growth, gulls and some fish come by to snack off your hull and the sound
can be fairly disconcerting. Critters, whether onboard of not, usually
quit what they're doing when you make noise, so it can be hard to tell.

Thought2: Feed it - on traps of you like. Rats do like to eat, so if you
leave food around, and you have a rat, it should show signs of
interest. Leave the boat for a few hours after setting the food, so any
critters will venture out and take the bait. If it eats, start trying
out baits until it gets caught.

Thought3: Most domestic cats are the crock - they don't know/care squat
about rats and mice. Cats _can_ be total sure death to small critters
(at least up Jack rabbit size), but it takes an "outdoor" cat with an
appetite who was raised right by Mama. This is a rare combination these
days. Also, rats are not your typical rabbit. You may have some vet
bills or lose the cat to disease.

Speaking of which, if you _do_ have a rat, handle as little as possible
and disinfect afterwards.

Rufus