how you do that?

If you wanna know how to do its, its quite easy. You HAVE to do this BEFORE the invasion starts though, because once Jolly Rodger's ship pulls up, theres like an invisible wall surrounding it. You have to do the Port Royal glitch, with the rocks near the dock, and use it to go WAY out into deeper water. Try to keep swimming out farther for a good 30 seconds, and when the invasion starts, you should be near enough to go inside his ship :D XD