Dynamic Positioning System
The propulsion system
The propulsions system is made various elements pieces that are assembled in a single system for a total solution. The complete system includes the propulsion motors combined with the control system described in the previous section (Computerized System) offers a greater precision to the operation of lay barges for the laying of pipelines or sub sea cables eliminating the use of winches and the need of anchors movement with tugboats.
This system of propulsion includes propulsion mechanisms that combined with the computerized control system respond immediately to the maneuvering signal. For this it counts on steering components that allow the propellers or thruster to be rotated through 360 degrees in approximately 18 seconds. The main motor can be Diesel, Electrical with a hydraulic or mechanical final drive, this depending on the cost and installation factors for each case.
The system can produce a trust 25 to 30 pounds/HP of power, for this it is necessary to make the appropriate calculations taking into account factors such as current, winds, barge displacement and areas like building, cranes, welding stations where the wind exerts its force.
The integrated system is designed for each particular case where the nature and location of the work dictates special capabilities like a retractable system to raise propellers or thruster for repairs or to operate at shallow depths. The forces required from the propulsion system are calculated to maintain the barges in stable positions avoiding movement and consequent loss of pipes or bending during the pipe laying.
Factors to consider for an appropriate installation of the DPS:
1- Thruster location:
These should be located in places that assure fast and easy displacement of the barge from one position to the next and immediate response forces generated by to winds, waves, and currents. Furthermore, they should be located in an area that would not interfere with the pipes that are being laid. In other words, they should be placed in an area where the energy produced by the thrusters does not impinge on the pipes. Otherwise, the thrusters may cause damage such as bending of the pipes due to the turbulence generated by the thrusters.
The thrusters should not interfere with the pipe laying equipment nor reduce the available deck area.
The system must be retractile to permit operation in shallow areas.
The system should not be placed in an area that will interfere with docking operations nor occupy large areas causing unreasonable operating inconveniences to other support vessel.
The design should allow the maintenance and repair of submerged components such as propellers without the need of dry-dock facilities.
2- Thruster Capacities:
The thrusters should be sized to overcome the most unfavorable combination of wind, current and other forces expected during normal operations.
Various aspects such as the barge weight distribution, including its fuel load, pipes, and water in storage tanks should be considered. Any structure on the barge deck that might cause wind resistance such as building, cranes, and welding stations with windshields should be taken into account.
The thrusters should be capable of controlling the barge's advance, immediate stop, and backing up to prevent loosing or damaging pipes.
The thrusters should also have the ability to work efficiently with other barges tied to the lay-barge for pipe supply.