In a recent conversation with Wim Knoester, Director of Propulsion at Wartsila Ship Power, he described a new thruster design that his company has been working on targeted to the drillship and semi-submersible drilling rig sector.
As the image below shows, the thruster is angled downward at an 8 degree angle.
Although the angle of the thruster does give up a portion of the energy in the downward vector, which adds nothing to the performance of the thruster, the added benefit of keeping the thrust away from the boundary layer adjacent to the hull results in more than a 15 percent decrease in losses in performance according to Wartsila’s computational fluid dynamic analysis.
What does an a 15 percent efficiency gain really mean?
Mr. Knoester notes:
In case of the conventional straight unit, from the 100 ton of thrust that the thruster generates, 80 tons remains to keep the rig on its location. The rest, 20% is lost due to thruster-hull interactions.
For the 8 degree tilted thruster, more than 95 tons is available for dynamic positioning.
Esssentially, 20 percent of the usable thrust is lost from a conventional thruster due to boundary layer losses associated with the hull.
The Maersk Advance-class drillship and two Frigstad deepwater rigs being built at Yantai Raffles will be some of the first rigs to have these thrusters installed. Over 100 of these type of thrusters have been ordered so far according to Brian Fariello, Wartsila Business Sales Manager – Americas .