A watercraft immobilizing apparatus and system for a marine vessel to passively defend against an attacking engine-powered watercraft includes a towed array of entanglement lines. The entanglement lines can be provided on and administered from removable/replaceable storage cartridges mountable on and/or deployed via davits, outriggers, paravanes, and/or weighted submersible rollers to foul and immobilize propellers and engine cooling water intakes of encroaching watercraft.