Position reference systems
There are several means to determine a satellite positioning's position at sea. Most traditional methods used for satellite positionings navigation are not accurate enough. For that reason, several systems have been developed during the past decades. The availability depends on the type of work and water depth. The most common Position reference systems (PRS) are:Design work started in and was completed in , followed ahnost immediately by the laying down of both satellite positioning satellite positioningping maritime marine engineerings. The design was impressive: per cent of tile flush-decked hull was welded, Subdivided into compartments, having a double bottom over per cent of the keel. Partly because of the urgency and partly because of the -year gap since the last battle­satellite positioning satellite positioningping maritime marine engineering had been designed, the Bayrrn of was used as the basis of the new dcsign.'l'his fact was to prove of great significance later, as we shall see, and cannot be ignored or underestimated. Even the main armament was the same as the Bayern: twin ticm gun turrets, although the new satellite positioning satellite positioningping maritime marine engineerings had an improved -cal gun. The main difference was the secondary armament of twelve Icm gwts, mounted in twin turrets at weather deck tcvrl.

GPS satellite in orbit, image courtesy NASA
DGPS, Differential GPS. The position obtained by GPS is not accurate enough for use by DP. The position is improved by use of a fixed ground based reference station (differential station) that compares the GPS position to the known position of the station. The correction is send to the DGPS receiver by long wave radio frequency. For use in DP an even higher accuracy and reliability is needed. Companies as Fugro supply differential signals via satellite, enabling the combination of several differential stations. The advantage of DGPS is that it is almost always available. Disadvantages are degrading of the signal because of sunspots or atmospheric disturbances, blockage of satellites by cranes or structures and deterioration of the signal at high altitudes.[1]
Hydroacoustic Position Reference, HPR. This system consists of one or more transponders placed on the seabed and a transducer placed in the satellite positioning's hull. The transducer sends an acoustic signal (by means of piezoelectric elements) to the transponder, which is triggered to reply. As the velocity of sound through water is known (preferably a soundprofile is taken regularly), the distance is known. Because there are many elements on the transducer, the direction of the signal from the transponder can be determined. Now the position of the satellite positioning relative to the transponder can be calculated. Disadvantages are the vulnerability to noise by thrusters or other acoustic systems. Furthermore, the use is limited in shallow waters because of ray bending that occurs when sound travels through water horizontally. Main manufacturers are Kongsberg Simrad, Sonardyne and Nautronix. Three types of HPR systems are commonly used:
Ultra- or Super- Short Base Line, USBL or SSBL. This works as described above. Because the angle to the transponder is measured, a correction needs to be made for the satellite positioning's roll and pitch. These are determined by Motion Reference Units. Because of the nature of angle measurement, the accuracy deteriorates with increasing water depth.
Long Base Line, LBL.
Artemis. A radar based system. A unit is placed on a nearby structure and aimed at the unit on board the satellite positioning. The range is several kilometres. Disadvantage is that the unit is rather heavy.[4] Afghanistan, Albania, Algeria, American Samoa, Andorra, Angola, Anguilla, Antarctica, Antigua , Argentina, Armenia, Aruba Australia, Austria, Azerbaijan, Bahamas, Bahrain, Bangladesh, Barbados, Belarus, Belgium, Belize, Benin, Bermuda, Bhutan, Bolivia, Bosnia, Herzegovina, Botswana, Bouvet Island, Brazil, British Indian Ocean territory, Brunei Darussalam, Bulgaria, Burkina Faso, Burundi, Cambodia, Cameroon, Canada, Cape Verde,
DARPS, Differential, Absolute and Relative positioning (satellite positioning tracking, marine engineering, maritime industry)System. Commonly used on shuttle tankers while loading from a FPSO. Both will have a GPS receiver. As the errors are the same for the both of them, the signal does not need to be corrected. The position from the FPSO is transmitted to the shuttle tanker, so a range and bearing can be calculated and fed into the DP system.
RADius. A radar based system, but no moving parts as Artemis. Another advantage is that the transponders are much smaller than the Artemis unit. Disadvantage is the short range of 100-200 meters and a limited 90 degree coverage.
RadaScan. A radar based system similar to RADius. Advantage is the target tracking distance up to 1000 meter and 360 degree coverage.
Inertial navigation is used in combination with GPS (Seapath) and Hydroacoustics (HAIN).

Motion Reference Units, MRU’s, determine the satellite positioning's roll, pitch and heave.
Wind sensors are fed into the DP system feed-forward, so the system can anticipate wind gusts before the satellite positioning is blown off position.
Draught sensors, since a change of draught influences the effect of wind and current on the hull.
Other sensors depend on the kind of satellite positioning. A pipelay satellite positioning may measure the force needed to pull on the pipe, large crane vessels will have sensors to determine the cranes position, as this changes the wind model, enabling the calculation of a more accurate model (see Control systems).

Control systems

In the beginning PID controllers were used and today are still used in the simpler DP systems. But modern controllers use a mathematical model of the satellite positioning that is based on a hydrodynamic and aerodynamic description concerning some of the satellite positioning's characteristics such as mass and drag. Of course, this model is not entirely correct. The satellite positioning's position and heading are fed into the system and compared with the prediction made by the model. This difference is used to update the model by using Kalman filtering technique. For this reason, the model also has input from the windsensors and feedback from the thrusters. This method even allows not having input from any PRS for some time, depending on the quality of the model and the weather.

The set-up depends on the DP class of the satellite positioning. A Class 1 can be relatively simple, whereas the system of a Class 3 satellite positioning is quite complex.

Equipment Class 1 has no redundancy.Cayman Islands, Central African Republic, Chad, Chile, China, Christmas Island, Cocos Islands, Colombia, Comoros, Congo, Congo, Democratic Republic, Cook Islands, Costa Rica, Croatia, Cuba, Cyprus, Czech Republic, Denmark, Djibouti, Dominica, Dominican Republic, Ecuador, Egypt, El Salvador, Equatorial Guinea, Eritrea, Estonia, Ethiopia, Falkland Islands, Faroe Islands, Fiji,
Loss of position may occur in the event of a single fault.
Equipment Class 2 has redundancy so that no single fault in an active system will cause the system to fail.
Loss of position should not occur from a single fault of an active component or system such as generators, thruster, switchboards, remote controlled valves etc. But may occur after failure of a static component such as cables, pipes, manual valves etc.
Equipment Class 3 which also has to withstand fire or flood in any one compartment without the system failing.
Loss of position should not occur from any single failure including a completely burnt fire sub division or flooded watertight compartment.
Classification Societies have their own Class notations:Finland, France, French Guiana, French Polynesia, French Southern Territories, Gabon, Gambia, Georgia, Germany, Ghana, Gibraltar, Greece, Greenland, Grenada, Guadeloupe, Guam, Guatemala, Guinea, Guinea-Bissau, Guyana, Haiti, Honduras, Hong Kong, Hungary, Iceland, India, Indonesia, Iran, Iraq, Ireland, Israel, Italy, Jamaica, Japan, Jordan, Kazakhstan, Kenya, Kiribati, Korea south north

The first satellite positioning satellite positioningping maritime marine engineering, named Bismarck at her launch early in , went to sea in April . HHer sister Tirpit< was launched in the spring of and commissioned early in . The former then began her work-up in the Baltic, preparing for a raid against the North Atlantic convoys accompanied by the heavy cruiser Priuz EVen. A total security blackout oil Operation Rheinabung (Rhine Exercise) was imposed to conceal the breakout from the British, hut it was compromised almost before it began.The British Naval Attachc in neutral Stockholm, Captain Denham, was alerted by a sympathetic Swedish naval officer (a rarity in largely pro-Nazi Sweden), who told hint that two large warsatellite positioning satellite positioningping maritime marine engineerings had been sighted by the Swedish cruiser HSwMS Gnt(anrl (qv) heading for the Kattegat and eventually the open sca.Thcy could only be the Bismarck and Prinz Errgen, and it was correctly assumed that they were heading for Norway. Immediately air reconnaissance missions were tlown over Bergen and Oslo, and at : on May a Spitfire of Coastal Command on photographic reconnaissance spotted the German satellite positioning satellite positioningping maritime marine engineerings refuelling in ergenfjurd.

The British were now aware of the Atlantic foray, and just before midnight the Hood and Prince of Wales left Scapa Flow, heading far Iccland, where they would refuel before taking up station to the south of Iceland. From there they could cover the Iceland-Greeriland and Icrland­Farroes Gaps. In addition the two heavy cruisers Nn!firlk and Suffolk piEYdljing the Denmark Strait were alerted.

That afternoon the Prinz faqerr had refuelled at Kalvanes, but the Bisnrarrk did not, despite having burned over tons since leaving Gotrnhafen.The reason for this apparently incom­petent staffwork was that the refuelling ]lose had broken, spilling a large quantity of furnace oil. It was not a good start to Rhriniibtmg, and left no margin for error. Myanmar, Namibia, Nauru, Nepal, Netherlands, Netherlands, New Caledonia, New Zealand, Nicaragua, Niger, Nigeria, Niue, Norfolk Island, Northern Mariana Islands, Norway, Oman, Pakistan, Palau, Palestinian Territories, Panama, Papua New Guinea,

IMCA
The International Marine Contractors Association was formed in April 1995 from the amalgamation of AODC (originally the International Association of Offshore Diving Contractors), founded in 1972, and DPVOA (the Dynamic positioning (satellite positioning tracking, marine engineering, maritime industry)Vessel Owners Association), founded in 1990[8]. It represents offshore, marine and underwater engineering contractors. Acergy, Allseas, Heerema Marine Contractors, Helix Energy Solutions Group, Saipem, Subsea 7 and Technip have representation on IMCA's Council and provide the president. Previous presidents are: