A sea trial is the testing phase of a watercraft (including boat

Boat

A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...

s, ship

Ship

Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

s, and submarine

Submarine

A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

s). It is also referred to as a "shakedown cruise" by many naval personnel. It is usually the last phase of construction and takes place on open water

Open Water

Open Water is a 2003 horror film loosely based on the true story of an American couple, Tom and Eileen Lonergan, who in 1998 went out with a scuba diving group, Outer Edge Dive Company, on the Great Barrier Reef, and were accidentally left behind because the dive-boat crew failed to take an...

, and can last from a few hours to many days.

Sea trials are conducted to measure a vessel’s performance and general seaworthiness. Testing of a vessel’s speed, maneuverability, equipment and safety features are usually conducted.