Depends. If you try to attack them with a jet then their defense system will shoot you out the sky if you get close. If you're in a boat then you can get on board but you won't be able to pull out your guns. If their defense system is off then you can attack them anyways you want unless they hired bodyguards to keep him safe lol
Too many smart dumbasses devoting their lives to sniping and/or RPG'ing you when you're on the deck. You'd think they would put two and two together with those cannons going off.
Only beef with the defense it is it looks like people with bounties can just camp on a yacht.