This summer, Wärtsilä delivered the biggest steerable thruster in its new thruster portfolio for Sleipnir, the world’s largest semi-submersible crane vessel (SSCV). As a feat of engineering, Sleipnir is impressive on multiple levels. The environmentally friendly LNG-powered vehicle features two revolving cranes that can lift up to 20,000 tonnes in tandem – that’s the equivalent of the Eiffel tower.
This summer’s delivery was the culmination of a five-year effort that began with conversations between Wärtsilä and Sleipnir’s owner, Dutch offshore contractor Heerema, in 2014.
Before the project began, Heerema studied market requirements and evaluated several vessel concepts, and concluded that it wanted a semi-submersible type hull for its new vessel. Based on past projects, Heerema knew that Wärtsilä would be a reliable partner for developing innovative new solutions to meet these requirements.
Lauri Tiainen, Director, Thrusters, Wärtsilä Marine Business, notes that close collaboration between Wärtsilä and Heerema throughout Sleipnir’s development was integral to the project’s success.
“Having a direct customer [Heerema] involved in the development helped better align the development with the customer’s desires. So, we came together and said, let’s commit to doing this together,” Tiainen says. This cooperative process allowed Wärtsilä and Heerema to develop the never-before-seen technologies that made Sleipnir possible.
First-of-its-kind technology
Through joint discussions, Wärtsilä and Heerema developed 360-degree rotatable, retractable thrusters with underwater mountability for Sleipnir. The project is the first time both retractability and underwater mountability features have been brought together in a single thruster design.
The underwater mountability was especially important.
“Because Sleipnir is so big, there are only a handful of dry docks in the world that a vessel this big can enter,” says Tiainen. “Thus, from a risk mitigation perspective for the customer, not having to go into dry dock for assistance is valuable.”
In addition to their unique design, Sleipnir’s thrusters are also mounted at an 8-degree downward angle. Tiainen explains the rationale: “From Wärtsilä’s research in hydrodynamics, we’ve found that this angle ensures water isn’t pushing against the ship’s hull. It doesn’t make sense to burn a lot of energy to produce water flow if it’s hitting your own vessel. This configuration — which minimises that problem — is much more efficient and effective both for moving the ship forward and keeping it stationary. With these thrusters, the ship can travel the globe fairly quickly with its own thrusters, which allows it to cover the broad geographic area that’s needed to fulfill jobs. With the thrusters, the ship can also be maintained very precisely in position during lifting jobs.”