Q&A Windfarm webinar
Can you explain in more detail how 8° tilt improves performance?
NORBERT BULTEN: The idea is that the jet of the thruster creates higher velocity water, and if that goes along the hull surface you create more friction. The 8° tilt deflects the jet sufficiently downwards meaning there is no interaction and no loss. An additional benefit is you can use your tilted units even in transit.
How does the plug-and-play system help the yard and the owner?
ARNOUD DINSLAGE: It’s a direct benefit for the shipyard thanks to the easy installation and limited number of connections, as it is already pre-aligned. For the owner this is a benefit in maintaining the building schedule, and for designers there is the advantage that we already have the designs ready. Installation can even be witnessed by Wärtsilä Field Services remotely, meaning travel restrictions don’t hold up the building schedule.
How does integration help create a complete system?
ARNOUD DINSLAGE: Controls and thrusters are already integrated as thrusters have their own control cabinet. There is also integration with Wärtsilä’s DP solutions, and you can increase the integration with the power management system for more potential gains. But it’s not only connecting systems, it’s also about sharing knowledge between different parts of Wärtsilä and working together on things such as CFD. We’re very much a team from the early design phase onwards, ensuring a total optimised integrated package with the added benefits of a single source of supply.
How does CFD simulation benefit from early customer engagement?
VINCENT BAST: The strength of CFD simulation and analysis in the early stage of a project is it allows you to analyse the interaction between thrusters and the vessel. We have seen cases where we have changed the thruster locations to improve efficiency based on their interaction with each other and with the hull shape; we’ve even adjusted the hull shape. We have over 25 years of experience in optimising vessels in this way.
What is Wärtsilä doing to solve environmental challenges such as noise?
MARK KENEFORD: When we talk about underwater radiated noise (URN) we have an extensive reference list of research and other vessels where low URN is a requirement. Our engineering teams have extensive experience in propeller design and understanding the best technology to reduce URN. My main message is to contact us to take advantage of our understanding and capabilities in reducing noise in propulsion systems.
What happens with retractable thrusters during transit, or are they only used for DP?
NORBERT BULTEN: In the past retractors were only intended for DP, so you would retract them to eliminate interaction with the hull. We designed our tilted units for DP operation, but we also made CFD simulations to show what happens with flow in transit operation. We noticed that the elimination of hull interaction losses is also valid in transit, so you can use any tilted thruster in the bow section if you need extra propulsion, for example in adverse weather, or to unload your aft units for better overall efficiency.
How are thrusters helping to meet environmental regulations?
ARNOUD DINSLAGE: There is a big risk of possible oil leakage at sea. To counteract this, you can use environmentally acceptable lubricants (EALs) or you can apply a shaft seal with a barrier. We can help with both these options.
NORBERT BULTEN: A lot of underwater noise comes from cavitation, and that is something we are addressing in our propellers and thrusters. Reducing it is well within our scope.
How do you decide the thruster positioning?
NORBERT BULTEN: It depends on the overall system because it has to provide a certain amount of force, so there isn’t one definite answer – it is vessel specific. We have seen cases where changing the position of the retractable thrusters, from the centre line or side by side, does make a difference to performance.
As wind turbine installation takes place in reasonably shallow water with higher currents, should DP thrusters for these applications be designed to be more effective under these conditions?
VINCENT BAST: We also see deeper waters with higher currents and challenging conditions. You need to take your operating conditions into account in the DP analysis, which we carry out using the Wärtsilä OPTI-DP tool. The tool considers thrust
degradation due to currents, with more degradation the higher the current. But you also need to take into account optimum propeller design, which you can adjust to improve your efficiency if you will be operating in higher currents.
NORBERT
BULTEN: High propellers with low loading are even more vulnerable to thrust degradation, so you should avoid them if you’ll be working in these conditions. We take all these aspects – wind, waves and current – into consideration in our
designs, ensuring the final configuration takes all environmental and physical factors into account.
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