Privateer: Privately owned vessel a state at war to attack enemy ships, usually merchant vessels.

武装民船： 为交战国征用以攻击敌方船只（常是商船）的私有武装船只。

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Whereas the latter is a state owned vessel, however (it belongs to Sheikh Mohammed bin Rashid al-Maktoum, the Crown Prince of Dubai), the Al Salamah is in private hands, and although she is smaller -- a mere 140 meters (457ft) long and 23.5 meters (77ft) wide -- she remains the largest, and most luxuriously appointed non-state vessel currently cruising the high seas.

CNN: Al Salamah: The ultimate yacht