Welcome To Dynamic Positioning (DP Basic) A free information resource for those marine officers interested In becoming a DPO or for anybody who is just curious.
An introduction about DP Basic its application on offshore vessels.
What is Dynamic Positioning or DP as it is commonly known well with regards to sea going vessels; it is, quoting from the DP Operators Handbook (Capt D Bray NI 2011).
"A system which automatically controls a vessel's heading exclusively by means of active thrust."
This appears to be the most widely used definition so that's what we will adopt for Dynamic Positioning Basic net..
The system may also be required to perform a number of planned operations
To expand on that a little it is a computer-controlled system that gathers information by interrogating a number of other systems which include P.R.S. position reference sensors, wind speed and direction sensors, MS motion sensors or V.R.S. vertical reference sensors as well as directional information from gyro-compasses.
All these sensors feed important information into the computer relating to the vessel's heading and position and the magnitude and direction of environmental forces that may impact on the vessel station keeping abilities.
The primary function of dynamic positioning systems is to keep the vessel or mobile unit in the desired position and to maintain a specific heading.
or tasks within certain criteria set by the dynamic positioning officer and also to perform those tasks in the most economical way to minimising not only fuel consumption but wear and tear on the propulsion equipment. Some times these operations are referred to DT (T= tracking) such as auto track etc. but for the purpose of this site we will refer to its common and familiar term throughout
In essence all DP systems basically perform within the same philosophy. However systems can range in complexity from a basic simplex system Class zero to one (1) that you might find on offshore utility and wind farm transfer boats to highly sophisticated and complex triplex systems
with full redundancy (I.M.O. D.P Class Three (3)
which would include diving vessels and offshore construction and crane ships.
At its most elementary the controller which is at the heart of the system will endeavour to calculate the difference between a desired position and heading set point values which are manually input by the Dynamic Positioning Officer (D.P.O.)
or the Officer of the Watch (O.O.W.) and the present position and heading of the vessel. The controller will then calculate how much force the propulsion systems should apply in any particular direction within the three horizontal degrees of freedom namely surge sway and yaw in order to reduce that difference to a minimum. (See 6 degrees of freedom)
In order to achieve its objective the system requires continuous input
of data from a range of external sources that include, but possibly not limited to; P.R.S position reference systems (both absolute and relative) such as differential global positioning systems DGPS,
hydro acoustic systems, taught-wire radar
and laser-based systems.
The controller also requires environmental data from sensors, M.R.U. motion reference units and (V.R.S.) vertical reference systems
in order to calculate the remaining other 3 degrees of freedom namely heave, pitch and roll in order to compensate for the environmental impact on the vessel’s model. The system also requires input from the heading reference systems, usually an array of several gyro compasses although solid state fibre optic compasses are becoming quite commonplace in some sectors.
All these sensors in the field contribute to the continuous feedback to the computer controllers.
These measured values are then used to calculate the error or deviation through a complex mathematical modeling
process and apply corrective action to keep the vessel on the station.
Mathematical modeling is a method of simulating real-life situations
with mathematical algorithms or equations to predict their future behaviour. Mathematical modeling
often uses tools such as decision-theory, queuing theory, and linear programming, and requires large amounts of number crunching. The mathematical model of a vessel is basically an accurate description of the vessels hydrodynamic which is used to compare and predict the vessels future with regard to heading, position and speed from the measured data input from the sensors in the field and calculate the possible environmental impacts on the vessel and compensate appropriately
A mathematical model can be the best way to break everything down
and predict how something new will play out. However as much as we would like it is not a perfect world and the model unfortunately is never 100% perfect. It is therefore necessary to introduce some kind of filtering whereby the model is able to continuously correct itself. The process by which this is achieved is by using Kalman filtering or extended Kalman filtering by which the model is continuously corrected.
Understanding Kalman filtering and how it is applied is not the easiest subject to grasp. We will cover it further on but only to the extent that is required. If you really are a purist you can read more about Kalman Filtering in this pdf downloadable article
or on the Wikipedia Page Here
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Dynamic Positioning DP Basic E Learning
A free e-learning portal to help those who wish to know just a little more about it
This site is not intended to be to be anything more than what it is, a very elementary insight into the subject.
For those who want to know more and are considering a career or training as a Dynamic Positioning Officer they should look at the available routes through the recognized entities which are at the moment the NI Nautical Institute DP Scheme and the alternative D.N.V. D.P.O. Certification route. There is a lot of information available on the web. A Good place to start might be The Dynamic Positioning Committee of the Marine Technology Society or II.D.P.O.A. The International D.P Operators Association. Also out soon our Dynamic Positioning Basic FAQ. The Dynamic Positioning Officer A New site of interest-Offshore and Marine Jobs