Blood Voyage (1976)

No man is an island, but stick a dozen or so disparate and desperate people on an open-sea pleasure craft and then have a secret murderer commence killing them off one by one and chances are any survivors will be wishing they were on some isolated land tract surrounded by water rather than trapped upon a harrowing Blood Voyage (1976). Of course, if a man must brave surreptitious psycho slayers out in the middle of the vast ocean, he deserves to be accompanied in his perilous travels by three sets of neck-snapping floatation devices, the presence of which racks up enough points of interest to make Blood Voyage a trip worth taking, if only to stimulate pelvic circulation.