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 seaworthiness. Testing of a vessel’s speed, maneuverability, equipment and safety features are usually conducted. Usually in attendance are technical representatives from the builder, governing and certification officials, and representatives of the owners. Successful sea trials subsequently lead to a vessel’s certification for commissioning and acceptance by its owner.
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 ITTC, SNAME, BMT, regulatory agencies or the owners. They involve demonstrations and tests of the ship's systems and performance.
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% MCR) The ship's heading is adjusted to have the wind and tide as close to bow-on as possible. The vessel is allowed to come to speed and the speed is continuously recorded using differential GPS. The trial will be executed with different speeds including service (design) and maximum speed. The ship is then turned through 180° and the procedure is followed again. This reduces the impact of wind and tide. The final "Trials Speed" is determined by averaging all of the measured speeds during each of the runs. This process may be repeated in various sea states.
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 used exclusively for passenger ships but now used in a variety of vessels. Involves 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]
- RMS Queen Mary 2 – Her trials were conducted over two periods, September 25–29, 2003 and November 7–11, 2003, each lasting four days at sea, shuttling between the islands of Belle-Ile and L'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.[6]
- USS Thresher (SSN-593) – Lost during deep sea diving tests on April 10, 1963.
See also
- Dock trials, a demonstration of the functionality of ship's equipment. Usually conducted alongside prior to sea trials.
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
- ↑ Plisson, Philip; Queen Mary 2: The Birth of a Legend; Harry N. Abrams, Inc, Publishers; 2004; ppg. 24- 25