I would have a band of kobolds led by a leveled kobold sorcerer or two and allied with a dragon turtle. Emphasize their reptilian heritage with the alliance.
Have the dragon turtle wait below the surface while the kobolds sail up on the target, then they signal and the turtle comes up and breathes on the deck crew of the target ship. Since it is superheated steam, it won't set the boat on fire, but should kill most of the crew. The kobolds then swarm aboard and take care of any remaining crew - the sorcerers can use enchantments to take out any stubborn crew members. If the target proves too difficult, the dragon turtle could use a second breath weapon attack or, in a worst case scenario, capsize the target ship.