[Davy]

Walk to the front gun of a War Sloop. Then walk towards the cannon from the front. Once your character starts moving off the edge of the ship, walk out to sea. That is to go underwater. For floating, repeat the same process but instead of walking out to sea, walk a few steps then walk back to the ship. Do not jump over the bar. Then walk back out to sea, and you will go up into the air.