Studies confirm DP rudder propeller efficiencies

The SRP-D was launched in 2022. In addition to the embedded electric main drive (LE-Drive) and a propeller shaft with an eight-degree tilt, the SRP-D features a number of improvements, including reduced propeller acceleration/deceleration times and a high-speed azimuth steering system with reinforced gear components, thus achieving double the rotational speed.

Efficiencies Assessed By Studies 

A joint study with MARIN and Polish ship designer MMC investigated the effect of thruster response latencies on DP positioning. The study found that the SRP-D rudder propeller demonstrated much-improved position accuracy and enhanced operability of the vessel. 

A separate study was conducted with DNV and Norwegian ship designer VARD in which the solution’s performance was simulated to assess the effect of the SRP-D on a service vessel’s operational performance and environmental impact. The study that the DP footprint can be significantly reduced, coupled with expected fuel savings of up to 30 percent depending on the operating point.

Michał Olko, Vice-President and Chief Designer, MMC Ship Design commented that “the results presented in MARIN’s dynamic DP simulations indicated a significant benefit as regards the operability of the vessel. We’re convinced that this fast responsive thruster will be the preferred choice for SOVs, allowing them to meet operational requirements in terms of DP accuracy and overall performance.”

Higher positioning accuracy

The dynamic properties of the SRP were investigated within a time domain level three analysis commissioned by classification society DNV. The simulation was performed on the numerical model of a real Service Operation Vessel (SOV) equipped with SCHOTTEL propulsion systems. Its position-holding capabilities were examined under extreme weather conditions: high winds, strong currents and effective wave heights of 2.5 metres and 3.2 metres. The results of the extensive simulations at DNV showed a significantly improved positioning accuracy while halving the DP footprint. This permits successful gangway landing operations even in rougher conditions, thus increasing the service life of the vessel throughout the year. Furthermore, every single landing is performed more efficiently, saving time and fuel.

Luca Pivano, Principal Specialist DP Simulations, DNV added “Our simulation results show that with faster thruster response the vessel’s station-keeping performance is greatly improved, resulting in smaller DP footprints compared to traditional thruster response. This benefit is even more obvious in harsh weather conditions.”

Increased propulsion efficiency

Thanks to the lower gearbox that has an additional eight degrees downward tilt, the interaction between propulsion unit and hull and the propeller flow interaction are reduced. As established in the simulations, these optimizations result in an increased thrust efficiency during DP. Depending on the thruster’s operational direction, simulation also revealed up to 50 percent less thrust loss and fewer forbidden zones.

Karl Randle, Principle Naval Architect, VARD: “The CFD results of the inclined gear box clearly show a significantly reduced thruster hull interaction or Coandă effect for zero-speed station-keeping. This is especially evident for inward flow directions and areas where the flow interacts with or flushes the skeg or other thrusters. The benefits of reduced thrust deduction could be significant for designers and owners in many applications when such considerations are included in detailed analysis procedures.” 

Savings in fuel consumption

Furthermore, the implemented optimisations yield additional savings in fuel consumption. Thanks to the faster response time of the propulsion, the vessel can be quickly held in position with only minor corrections being necessary. This prevents major corrections in position having to be made which would require more power. Depending on the operating point and environmental conditions, this can save up to 30 percent in fuel during DP operation compared to standard rudder propellers.