a shaft-less propulsor to minimize impact of floating ropes and debris

by Fredrik Falkman, SSRS

Subject Mass Rescue, Operations, Rescue
Status Ongoing
Results Working Prototype
Owner Type Businesses, Rescue organizations

This video shows two low speed rim-drivven thrusters taking turns chewing on a rope. A water jet would have jammed immediately. 


Ship accidents usually produce lots of floating debris. Rescue boats, weather equipped with a water jet or a propeller, are vulnerable to debris, an can be made useless for hours by a rope that gets tangled and melts into a solid mass around the shaft. Contaminated water can lead to loss engine cooling.


A shaft-less propulsor will reduce the risk of getting stuck by debris. A fully electric solution would mean less complexity and maintenance, and no need for a cooling water system that could be compromised by other containments.


We hope to develop and test a fully electric Rim-Jet prototype for small rescue boats. Here’s a list of specs we ar currently aiming for:

  • >4 kN bollard pull
  • Optimized for moderate planing speeds 20-25 Kt
  • 50-70 kW


Principal design of a Rim-Jet. Image courtesy of Thor Peter Andersen

Principal design of a Rim-Jet. Image courtesy of Thor Peter Andersen


After years of searching for suitable technology, the project finally took off as a collaboration with Norwegian firm Marna, who are developing a rim driven permanent magnet motor through likewise Norwegian firm SmartMotor (now a subsidiary of Rolls-Royce).


The Marna/SmartMotor prototype with a 3D-printed dumb impeller

Two separate Master Theses projects in Hydrodynamics (by Thor Peter Andersen, Chalmers, See his report below!) and Mechanics (by Kiran Ashok Naganalli, KTH) have been conducted at Rolls-Royce Kamewa in Kristinahamn, Sweden, to determine feasibility. We are currently looking into further developing suitable bearings to eventually finish a working prototype.



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Who is behind the project?

This is a project from the Innovation office at Swedish Sea Rescue Society, SSRS. The SSRS is a non-profit organization that performs the majority of sea rescues in Sweden thanks to some 2000 volunteers. Our constitution says that we are to:

  • Further the interest in sea rescue matters
  • Propose ways to improve sea rescue
  • Perform sea rescue operations

The person proposing this project is me, Fredrik Falkman. I’m an industrial designer by training working for the SSRS with development projects and general innovation. Beside my work at the SSRS, I run a design consultancy: Fredrik Falkman Design AB, FFD.


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