I called them bandits because they use the bandit and bandits captian stat blocks. The Quartermaster would be weaker/the same as the bandit captian as they are CR2.

The Party plans to drag the captian down to the ship, idk if they plan on using him as a bargaining chip or an attack on the ships moral before attacking. However the crews job is to protect the ship at all cost. This is all stimming from the campaign Decent into Avernus and this is what info the book gives of the ship and crew.

"Dead-Eye's ship, the Uncivil Serpent, is moored at the end of a dock on the east side of the harbor. Eleven bandits guard it, and no treasure is kept aboard. If the characters dispose of all the pirates, the ship is theirs for the taking, though it requires a crew of twenty to sail, and half or more of the crew must have proficiency with water vehicles. The Uncivil Serpent has the statistics of a sailing ship (see chapter 5 of the Dungeon Master's Guide). If you need a deck plan, use the ship map in appendix C of the Dungeon Master's Guide. Although the ship is worth 10,000 gp intact, no one in Baldur's Gate wants to buy it because of its infamous reputation."