The only thing keeping this movie from being goddamn amazing is the fact that Michael Caine clearly doesn't give a shit about being in it.
Beyond the lead actor not even trying, this is a balls-out fucking ridiculous movie. David Warner leads a gang of inbred buccaneers(!), descendants of a forgotten 15th Century pirate band(!!), who are sweeping the Caribbean clean of yachts and fishing boats. Caine and his kid wind up on David Warner's Hidden Pirate Island (!!!) and are forced to join their society. What follows is madness as the pirates attack vacationers and drug smugglers, Caine tries to escape, and his son gets brainwashed into becoming Warner's heir (brainwashed, like, really easily. Two days, tops).
It's weird as hell, and very spotty in parts, but totally worth a watch. Just the fact that the archetypal fun swashbuckling music plays while these grungy assholes are cutting sleeping people's throats or gutting Coast Guardsmen is amazing.