Most Navy boats have permanently assigned crews. Crew size varies depending on the type of boat, but typically consists of the coxswain, engineer, and bowhook and sometimes a sternhook and boat officer. All must be qualified swimmers. The boat crews represent their vessel and should for that reason take pride in their appearance and that of their boat. The efficiency and smartness of a ship's boats and boat crews reflect the standards of the ship. Clean white uniforms can be hard to maintain on some ships, but custom dictates that every day the ship's laundry wash and press a uniform for each member of the duty boat's crew. Ship regulations frequently require crew members to wear sneakers. This is a safety factor, but it also keeps the boats themselves looking good.