D.P Vessel stands for dynamic positioning vessel which maintains its
position (fixed location or predetermined track) by means of active
thrusters. These vessels does not need anchors to dock and can stay
fixed to any position on the sea based on satellite g.p.s signals with a
precession of 99.9% making it more safer and reliable. The advantages
fully operated by DP ships include the ability to operate with a
positioning with the precision and flexibility to define the position
and enable rapid positioning without the need for anchorage. This made
d.p vessels quite useful, maybe the only reliable source for
research/Exploration/Drilling(Sea bed).
What is D.P(Dynamic Positioning ) Vessel used for?
D.p
vessels are used worldwide mostly by Deep sea explorers, Scientists and
deep sea oil diggers in the form of semi submersible oil rig, offshore
support vessel, and Research ship. They are used over others types of
ship in these work as for digging for oil one need to be very steady to
avoid any uneven stress being generated during digging sea bed, It is so
in the case of deep sea diving where for the divers safety the ship
must not move much from its original position as it may break life line
connected to the divers during exploration. It is also required to stay
steady during bringing something off-sea from the sea bed with the help
of crane to avoid unwanted drag and forces to be eliminated.
"Typical DP ships include survey ships, drilling vessels, work boats, Drilling platforms, diving support vessels, cable layers, and supply vessels."
How does D.P(Dynamic Positioning ) vessel work?
The first DP
vessel was used in the early 1960s and work on conventional PID
controllers in cascade with low-pass notch filters to suppress the
first-order wave-induced motion components. But from the mid-1970s, more
advanced and sophisticated control techniques were proposed based on
linear optimal control and Kalman filter theory.
A
computer control system automatically keeps the position and direction
of a ship's with the help of its own propellers and engines. Positional
reference sensors, combined with wind sensors, motion sensors and
gyroscopes provide information to the DP computer about the position of
the ship and the magnitude and direction of the environmental forces
(wind and waves) that can influence their position.
The
computer program contains a mathematical model of the ship containing
information about the air resistance and the ship's current location and
propellant. This knowledge, combined with sensor information, allows
the computer to calculate the steering angle and the force required for
each pressure propeller.
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| Image credit: wikimedia.org/wikipedia.org |
Class Requirement
Based
on the publication of IMO (International Maritime Organization) the
classification societies have described rules for dynamically positioned
vessels under Class 1, Class 2 and Class 3.
- Class 1 devices do not have redundancy. The loss of position in case of a single error can occur anytime.
- The class 2 team redundancy, so no single error in an active system causes the system failure. The loss should not occur due to a component fault or an active system, such as generators, engines, tables, remote control valves, etc., but may occur after a failure of static component, such as cables, pipes, manual valves, etc.
- Class team 3 must also be able to withstand fire or high water in a compartment without system failure. Loss position will not be expected for failure, which includes a subdivision in fire/water or flooding in completely sealed chamber.
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Various books, study material and other online sources has been
refereed prior to writing this article but no part is copied or
produced from any of the source but explained same thing in better
detailed way.
Cover image Credit: http://www.offshoreenergytoday.com
Author Amit Article Requested By: Indralal Gunaratna
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