Even more than the engine of an ordinary ship, the thrusters of a dynamic positioning vessel must be available virtually every second. Hundreds of thousands of dollars in daily revenue, the on-time completion of multimillion dollar subsea construction projects, and sometimes even subsurface workers’ lives, all depend on the vessels’ six thrusters maintaining position within a few metres all the time.
Wärtsilä had found a solution from Helix Energy Solutions Group’s MSV Q4000 that not only boosts reliability but increases the efficiency of the ship’s engines, makes more power available to the distribution network and thus removes the need to install dedicated alternators for a new drilling package. However, since the Q4000 went into service, there had been reliability issues with the auto-transformers used to start the original fixed speed motors – a serious problem for a vessel designed for a high-performance task.
Engineers at Wärtsilä Automation Services devised a solution to correct this problem: a variable speed drive for the thruster motor. Not only is a variable speed drive more reliable owing to the solid state components of the system, it also improves the thruster’s performance, boosting operating efficiency of the power network from 50 to 80%. Greater efficiency means less wear and tear on the engine. Since the thrusters are not turning at maximum revolutions all the time, the thruster drive chains age less quickly.
This results in substantially lower power consumption. Prior to the conversion the vessel consumed around 40 cubic metres of Marine Diesel Oil (MDO) per day. Since the conversion, daily consumption is now just over 20 m3 – a savings of nearly 50%.
Boosting capacity and saving money
The Q4000 thruster controls upgrade has given operators greater control over the vessel, since it can now operate at a lower power load and wide range of speed. Wärtsilä’s innovative use of a “quasi-24 pulse” arrangement of the thruster drives reduced capital outlay and installation costs.
At the same time, the upgrade gave the vessel a variable speed thruster control system which produced a very low harmonic distortion on the vessel’s distribution network. The installation of variable speed controls allows the vessel to run longer on the same amount of fuel, enabling the operator to cut the vessel’s energy bills or to eliminate altogether the need for a new engine to power the Q4000’s drilling package.
Drilling upgrade
At the same time with the thruster upgrade, Helix installed a complete modular drilling package on board the Q4000. Wärtsilä provided the engineering, materials and installation of the electrical supplies for the drilling package which included an 11,000V switchboard extension and also more variable speed drives for the hex pump motors. It is worth noting that the new drilling process loads created a demand for more MW of power from the vessel. Due to the efficiency improvements gleaned from the thruster drive upgrade, no new generators were required to feed the drilling package, a huge savings in capital, maintenance costs, and environmental impact.
For the Q4000 thruster upgrade, we found a viable concept, engineered the change, integrated the new systems with the vessel’s existing equipment, and then stood by our client all the way through the commissioning and sea trials.
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