How do you sail?

[searage]

There is a bug/feature where sometimes when you get a ship down to negative health, it wants you to board it. You'll know when this happens because a) no amount of shooting the ship will make it sink, and b) there will be a bunch of vertical green circles along the edge of the deck for you to shoot grapping hooks at. These are very small and hard to see unless you're close, but they are there. If you shoot the grapping hooks at each of the circles and hit them, you can press Control to swing over to the other ship for some sword fighting.

I don't know what happens after that. Since I'm perputually sailing alone, I just skip that ship and move along to a new ship. There are too many weird pathing bugs fighting on decks, not being able to get back to your ship issues, client restarts, etc. I've never successfully captured a ship in this fasion, so I just stopped bothering with it.

No idea what makes the game decide between sinking the ship and making you board it. Anyone else know?