@zx7t I can give you a valuable tip but it has its risks.
If you start a session solo and you're on an island looking for treasure, keep an eye out for those gunpowder barrels. Take them on board and place them on the crows nest. That way you don't get sunk when they explode.
If you get chased by a galleon then turn your ship against the wind, wait till they're perfectly lined up behind you. Look in front of you to make sure that you don't hit any rocks or islands.
Restock your Ammo and Bananas, pick up the gunpowder barrel and jump off your ship.
Wait till the Galleon is close, drop the barrel and swim away from it asap and try to grab their ladder. By that time, the barrel already exploded, probably knocked 1 or 2 guys off the ship and you can drop their anchor and finish the rest.
Highly risky, highly rewarding and won't work always but it is a chance to get rid of them that way.