Treasure to Ship

There are 2 pirates and 4 treasure chests on an island. The pirates have 1 small boat to take the treasure to their ship. The boat can take 2 pirates or 1 pirate and 1 chest of treasure.

How many trips do the pirates have to take to get all the treasure and both pirates onto the ship?

Note: The ship needs 2 pirates to sail it. Don't worry about one pirate sailing off with all the treasure!