One of the main disadvantages of dynamic positioning systems when compared to mooring systems, is the fuel costs incurred in operation. But it is necessary to quantify that difference in order to make an informed choice between the two possibilities: mooring or dynamic positioning.
In Ref , a comparison of fuel consumption between a passively moored FPSO and a Dynamic Positioned FPSO is made. The arrangement of the two versions are show in pictures on the right. The moored version of the FPSO has an internal turret with 3*3 chain mooring arrangement. The DP version of the FPSO has a thruster layout consisting on 7 thruster units.
The following simulations were carried out:
The analysis considers a typical annual scatter diagram of sea states for the Gulf of Mexico. The results are summarized in the table below:
|DP FPSO||Annual Average consumption||6,930.7||1.7|
(DP system out)
|Annual Average consumption of ship systems = 2.5 MW||6,428.4||1.6|
|Diference = 0.1|
|Process Plant||Gas Turbines 2*25MW|
30 MW load
Resume and analysis:
If we do a gross estimation of the potential number of “seastead apartments” available on the FPSO, we obtain following results:
Length = 262.4 m
Beam = 46 m
Main Deck space = 10,863 m2
Number of decks = 5.00
Total deck space = 54,317 m2
Average space apartment = 100 m2
No. Apartments = 543
=> DP fuel cost per month and apartment = 15 €
That means that the cost per “seastead apartment” is quite low and shows that a DP system need not have high operating costs, for a big vessel such as this, with a somewhat hydrodynamic shape.
 Aalbers, Albert B.; de Vries, Leo; van Vugt, Hans. Fuel consumption and emission predictions: application to a DP–FPSO concept. Houston: Dynamic Positioning Conference, October 2006.