Armed guards would have to be UN sanctioned and trained. Rules of engagement would have to be pretty specfic *criminal act in progress*, preemptive deadly force will inevitably lead to killing/injuring innocent people. Armed guards on vessels with highly combustible cargo is akin to lighting a candle in a dynamite shack.

Convoys is probably the most feasible strategy. Develop better non-lethal measures from anti-boarding to safe/secure rooms with a kill-engine switch and/or lock the steering, and an auto emergency distress alarm from that secure space. If one can't prevent the boarding, at least deny them access to hostages and the ability to move the ship to their safe haven.

Accept the fact that piracy will always exist in some degree, and that recovering hostages by force will inevitably result in some of them getting killed eventually.