German propulsion company Schottel reports that the increased performance of its RudderPropeller Dynamic SRP-D has again been confirmed by external sources.
At the request of the Dutch Damen Group, the Maritime Research Institute Netherlands (MARIN) carried out extensive research to demonstrate the added value of the SRP-D for commissioning service operation vessels (CSOVs).
While an earlier study had demonstrated a reduced DP footprint and fuel savings, Damen’s latest research focused particularly on propulsion efficiency during thruster interactions. The results obtained show a significant increase in thrust yield as well as reduced forbidden zones with the SRP-D compared to conventional rudder propellers.
Mark Couwenberg, Damen Product Portfolio Manager SOVs, said: “In our continuous strive for offering optimal vessels to our clients, Schottel’s developments are a great step. The SRP-D thrusters mounted under Damen’s optimised hulls result in vessels with a smaller footprint while at the same time reducing fuel use and further improving comfort on board. Combined with Schottel’s robust methods of design, engineering and construction we are convinced that our clients will have life-long benefits by selecting this combination.”
With the SRP-D optimised for DP operation, Schottel is meeting the increased efficiency and reliability requirements for CSOV vessels. The thruster is marked by an additional 8-deg tilt of the lower gearbox and a vertically integrated electric drive motor (LE-Drive). In addition, the SRP-D is characterised by reduced propeller acceleration/deceleration times. In combination with a high-speed azimuth steering system with reinforced gear components, the SRP-D enables faster thrust allocation than conventional rudder propellers. Thanks to the shorter response times, it is possible to react faster and in a more targeted manner to external forces such as wind and currents, thus achieving a higher positional accuracy of the vessel.
The research was carried out on a model of a CSOV equipped with a Schottel SRP-D on starboard and a regular 90-deg thruster on portside. To perform the tests, the model was placed in a 45m long and 36m wide offshore basin. A three-component measurement frame with calibrated sensors was installed on the model for data acquisition.
The first part of the study measured the interactions between propulsion unit and hull. It was found that the additional 8-deg downward tilt of the SRP-D propeller shaft could significantly reduce thrust losses, both for azimuth variations and thrust variations. For example, CSOVs with 98-deg thrusters experience only 10% thrust losses in transverse direction, compared to 35% with 90-deg thrusters. The study shows that a key factor for the improved system performance is a reduced Coandă effect with the SRP-D.
The second part of the research focused on the propeller flow interactions. Again, significantly lower thrust losses occurred when operating CSOVs with the SRP-D: While 50% losses are observed when the 90-deg thruster is blowing the wake into the second thruster (in-line thrust losses), only 20% thrust losses occur with the 98-deg thruster. When the 90-deg thruster is blowing the wake into the second one while being perpendicular to it (transverse thrust losses), the thrust in transverse direction is decreased by about 40%, compared to 20% with the 98-deg thruster. In both cases, the 98-deg variant thus induces lower losses at the other thruster than the 90-degree variant and therefore enables a higher remaining force during DP.
The research shows that the additional 8-deg tilt of the SRP-D gearbox significantly optimises thrust yield and thrust distribution, since thruster-hull- and thruster-thruster-interactions are minimised. Consequently, the forbidden zones of the thrusters may be reduced, which leads to an additional increase of the DP performance for the vessel. Furthermore, CSOVs can significantly lower their fuel consumption and thus cut emissions. Overall, the vessels operate more efficiently and safely, extending operating time throughout the year.
Image: Results showed a significant increase in thrust yield with the SRP-D (source: Schottel)
