as far as defending against the pirates effectively, any gun will keep them back. remember, they're in a little open boat and VERY exposed. they've gotta have a solid brass set to approach an armed vessel in something like that. One good rifle (remember, the ship is a much more stable platform to fire from) a couple of shotguns and a couple of handguns are that are really needed to protect a ship. firing a rifle at them before they get within rpg range I'm sure will slow them down. nothing for them to hide behind, nowhere to run to, who in their right mind would approach? of course, firearms are useless if the crew is complacent and does not keep a good watch for suspicious vessels.