Sea trial
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A sea trial is the testing phase of a watercraft (including boats, ships, and submarines). 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, and it can last from a few hours to many days.
Sea trials are conducted to measure a vessel's performance and general
Although sea trials are commonly thought to be conducted only on new-built vessels (referred by shipbuilders as 'builders trials'), they are regularly conducted on commissioned vessels as well. In new vessels, they are used to determine conformance to construction specifications. On commissioned vessels, they are generally used to confirm the impact of any modifications.
Sea trials can also refer to a short test trip undertaken by a prospective buyer of a new or used vessel as one determining factor in whether to purchase the vessel.
Typical trials
Sea trials are fairly standardized using technical bulletins published by
Speed trial
In a speed trial the vessel is ballasted or loaded to a predetermined draft and the propulsion machinery is set to the contracted maximum service setting, usually some percentage of the machinery's maximum continuous rating (ex: 90%
Crash stop
To test a crash stop, the vessel is ballasted or loaded to a predetermined draft and the propulsion machinery is set to the contracted maximum service setting, usually some percentage of the machinery's maximum continuous rating. The trial begins once the order to "Execute Crash Stop" is given. At this point the propulsion machinery is set to full-astern and the helm is put hard-over to either port or starboard. The speed, position and heading are continuously recorded using differential GPS. The final time to stop (i.e.: ship speed is 0 knots) track line, drift (distance traveled perpendicular to the original course) and advance (distance traveled along the original course line) are all calculated. The trial may be repeated at various starting speeds.
Endurance
During endurance trials the vessel is ballasted or loaded to a predetermined draft and the propulsion machinery is set to the contracted maximum service setting, usually some percentage of the machinery's maximum continuous rating. The fuel flow, exhaust and cooling water temperatures and ship's speed are all recorded.
Maneuvering trials
Maneuvering trials involve a number of trials to determine the maneuverability and directional stability of the ship may be conducted. These include a direct and reverse spiral manoeuvres, zig-zag, and lateral thruster use.[1]
Seakeeping
Seakeeping trials were originally used exclusively for passenger ships, but are now used in a variety of vessels. They involve measurements of ship motions in various sea states, followed by a series of analyses to determine comfort levels, likelihood of sea sickness and hull damage. Trials are usually protracted in nature due to the unpredictability of finding the correct sea state, and the need to conduct the trials at various headings and speeds.[2]
Noteworthy sea trials
- RMS Lusitania – While steaming at high speeds, severe vibration was noted at the stern during her sea trials. This prompted her builder, John Brown & Company, to reinforce that area before acceptance by Cunard.[3]
- SS Normandie – During sea trials, vibration was noted at the ship's stern. The stern was reinforced, accepted by her owners Compagnie Générale Transatlantique, and continued onto her maiden voyage. The vibration was severe enough to necessitate relocating Tourist Class passengers and some crew members with cabins near the affected area. The problem was subsequently resolved by changing her propellers to four-bladed ones from the original three-bladed ones.[4][5]
- harbour pilot who had embarked on at Clydebank, and to maintain strict radio silence. Later that day, at the time when she was due to arrive at Southampton, the city was bombed by the Luftwaffe.[6] After a zigzagged crossing taking six days to avoid German U-boats, Queen Elizabeth had still crossed the Atlantic at an average speed of 26 knots. In New York she found herself moored alongside both Queen Mary and the French Line's Normandie, the only time all three of the world's largest liners were berthed together.[6] Captain Townley received two telegrams on his arrival, one from his wife congratulating him and the other from Queen Elizabeth thanking him for the vessel's safe delivery. The ship was then secured so that no one could board her without prior permission, including port officials.[6]
- ile d'Yeu off the French coast. On board for each set of trials were 450 people, including engineers, technicians, owner and insurance company representatives, and crew.[8]
- USS Thresher (SSN-593) – Lost during deep sea diving tests on April 10, 1963.
References
- ^ Lewis, Principles of Naval Architecture, Volume II, Section 15, p. 316 (Maneuvering Trials and Performance
- ^ Lewis, Principles of Naval Architecture, Volume II, Section 7.3, p. 140 (Seakeeping Performance Criteria and Seaway Response).
- ^ Ballard Robert F. & Spencer Dunmore (with paintings by Ken Marschall); Exploring the Lusitania: Probing the Mysteries of the Sinking that Changed History; Warner/ Madison Press; 1995; ppg. 22- 23
- ^ Ballard Robert F. & Rich Archbold (with paintings by Ken Marschall); Lost Liners; ppg 168, 170
- ^ Braynard, Frank; Picture History of the Normandie; Dover Publications, Inc., 1987; pg. 16–17
- ^ a b c d e f g h i Maxtone-Graham, John. The Only Way to Cross. New York: Collier Books, 1972, pp. 358–60
- ^ Floating Palaces. (1996) A&E. TV Documentary. Narrated by Fritz Weaver
- ^ Plisson, Philip; Queen Mary 2: The Birth of a Legend; Harry N. Abrams, Inc, Publishers; 2004; ppg. 24- 25