Swing into boarding range and start the action. You have a number of objectives to take over the man o war. Start by using the Swivel Gun to attack either the Captain or the Powder Reserves. Ignore the crew as you will have amble opportunity to kill them off once on board. Taking out the powder reserves and the Captain will reduce the number of men lost while on board.
When the ships are next to each other, hop on over and get on deck for fighting. Use your pistols on any remaining Powder Reserves immediately. Be careful as you can kill crew blowing them up so check your fire some. They all need to be blown up though. Just get on through the requirements and the boarding action will come to an end and the memory.