Ya know, for me, a simple solution is usually best ... I see the 50 cal M2 as about the max that could be moved around by a couple of people, sets up quick, and made secure below decks when needed. Hey put four out in advance.
IMHO — It’s about the biggest that is handy ... It should be good for sinking any of these pirate dingys.
Gatling guns scare the hell out of people just sitting there................