i think a shotgun is a pretty good choice. lots of choice in ammo selection.
i have an old street sweeper i keep on board. loaded with my favorite
homemade shells. very effective on tissue. also keep a 45. agree with crantz
on the 9mm. once shot an asshole 3 times with one. when they peeled his
clothes off at the hospital, one of the slugs fell on the floor. guy was
wearing a winter coat. last time i ever carried a 9. conditions on a boat
arent that great for accuracy long range. dont think a rifle would do you
much good. better to use close range stuff. hard to miss with a short
shotgun. wear a flack jacket. wont keep you from getting hit, but will buy
you a little time. flash bangs work well if you know where to get them. i
love the spray and pray guys. while shooting wildly with your 40 round clip,
someone with some training will install a 3rd eye in your ****ing head. best
thing to do is try to avoid the situation. if you cant, keep your cool and
kill everything you see. if youre good, and a little lucky, thats enough.
kind of new to sailing, but weapons and mayhem are something i know a little
bit about.

one more thing. there is no magic gun or bullet. carry what you can shoot. a
22 between the eyes is far better than a clean miss with a 44 mag.