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The history of DP
The history of the dynamic positioning
The very first dynamic positioning system was used in 1957, on the American ship CUSS 1. It was a primitive system, with four propellers but was possible to keep the ship in position above the well at a depth of 948 meters off La Jolla,California .
After this first well in the 1961, the ship did 5 drillings at a depth of 3560 mts, while maintaining a position within a radius of 180 mts. The position in relation to the seabed was found by lowering a transmitter down to the sea that transmitted signals up to the vessel (the first form of hydro acoustic reference system).
The idea of developing an automatic control unit to take care of the DP function was born.
Later in that year (1961) the American Shell Oil Company launched the drilling vessel EUREKA. In 1964 another vessel CALDRILL 1 was delivered to Caldrill Offshore Company, USA with similar DP on board. Both the Eureka and Caldrill worked very well, the first drilled at a depth of 1300 mts with 6 mts of waves and wind up to 40 knots, the second was able to drill at maximum depth of 2000 mts.
Then in 1963 was delivered the first French DP vessels, SALVOR and TEREBEL were laying pipelines in the Mediterranean.
A few years later started the oil adventure in the North Sea, Norway and UK became interested in the dynamic positioning.
Today the DP has changed a lot since the CUSS1 in 1961, is now being used for many different operations, geological, military, cruise ship manoeuvring in lagoons, drilling, pipelaying, accommodation barge, shuttle tankers, diving , heavy lift and construction.
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The purpose of DP
The main purpose of Dynamic Positioning is to keep a vessel in a specified position by control of the propulsion system.
The D.P. is designed to perform this task within a certain range limit, using a minimum fuel and with minimum wear and tear of the propulsion equipment.
The D.P. computer calculates the difference between the "wanted" position and the "present" position of the vessel, and then calculates the force that the propellers should produce in order to make the difference as small as possible.
The system controls the vessel's position in three horizontal degrees of freedom, called surge (ahead and astern), sway (sideways) and yaw (turning of the bow).
The computer use a mathematical model for calculate the force of reaction, that is based on a hydrodynamic description involving some of the ship's characteristics such as mass, drag etc.
The purpose of the model is to describe, as much as possible, the vessel's motion and reaction to any external forces.
The model is "driven" by the same forces as the vessel itself. These forces are wind and thrusters, and with algorithms the model is also able to calculate the sea current.
The model of course is never 100% perfectly as the "real world", but by using the so-called Kalman-filter technique the model is able to correct itself continuously in the following way.
The vessel heading and position are measured using gyro-compass along with one or more position reference system and sent to the computer.
These data are compared to the predicted data produced by the model and the difference are "filtered" by the Kalman-filter and then finally used to "tune" the model to the actual situation
How to get a DP Operators certificate
Certification of DP Operators
The following is an extract from the Norwegian Maritime Directorate, Guidelines and Notes number 23. This note is dated 15.06.93 and refers to Regulations of 4 September 1987 concerning anchoring/ positioning systems on mobile offshore units,6 section 5.6
02 - Anchoring/positioning - Certification of DP operators
Operators of dynamic positioning systems (DP systems) with the NMD's DP Consequence Class 2 or 3, shall be certified by the NMD. Certificates issued by The Nautical Institute (UK) are accepted as equivalent.
It is sufficient with one certified DP operator at each shift. Other DP operators should at least hold the basic course, ref. Item 1 below.
Certificate (DP Consequence Class 2 and 3)
1) Basic course at an approved training institution. The course shall provide an introduction to the functions and use of DP systems.
2) Documented practical DP experience on DP units/ships (irrespective of conse-quence class) for a minimum of 30 days.
3) Advanced course at an approved training institution. The course shall provide training in the use of DP systems including simulator exercises and emergency operations.
4) One of the following requirements shall be met:
a) 6 months' documented practical experience in the use of DP systems on units/vessels operating in Consequence Class 2 or 3.
b) 12 months' documented practical experience in the use of DP systems on units/vessels operating in Consequence Class 0 or 1. If this experience is from units/vessels which spend more than 50% of their operational time on DP, 1 month's practice on units/vessels operating in Consequence Class 2 or 3 is required in addition. If the experience is from units/vessels which spend less than 50% of their operational time on DP (e.g. Shuttle tankers or supply ships), 2 months' practice on units/vessels operating in Consequence Class 2 or 3 is required in addition.
5) The platform manager/captain on the Consequence Class 2 or 3 unit/vessel shall give written confirmation that the operator has the necessary practical experience, and that he assumes him qualified as a DP operator.
Validity of DP Certificates
DP operators shall keep a log of their DP practice in an approved log book. If the last documented period of DP practice on Consequence Class 2 or 3 units/ships is older than 5 years, the DP certificate ceases to be valid.
To renew an invalid DP certificate, items 3, 4 and 5 above have to be carried out once more.
Limited Certificate
(DP Consequence Class 0 and 1)
After request from the industry, the NMD has decided to allow the issue of a Limited Certificate for DP operators working on units/vessels with the NMD's Consequence Class 0 and 1. It is, however, provided that the DP operator meets the requirements specified in items 1, 2 and 3 above.
Discussion Forum
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The DP Operators startpage!!!
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