Thruster and podded drives are propulsion systems with strong hydrodynamic interaction effects between propeller and housing. These interaction effects and specific operating conditions (bollard pull for thrusters, manoeuvring, off design) make experimental as well as numerical investigations  a more challenging task than with conventional propellers. The experimental assessment of azimuthing propulsion systems covers open water, propulsion and cavitation tests.

During the last years SVA Potsdam have been successfully conducting several  research projects regarding pod forces, Reynolds number effects, ship design in connection with azimuthing propulsion systems, pods for high ship speeds, pods with HTS engines and manoeuvring of single screw ships with podded drives. The experience gained in these projects form the constantly broadening basis for our work in the field of azimuthing propulsion systems.

At SVA Potsdam different arrangements of thrusters and podded drives with pull, push, twin and contra-rotating propellers can be thoroughly analysed. With SVAs unique z-drives with six-component balances with internal rotary table the following quantities can be measured:
-    the forces and moments acting on the overall system and the thrust and torque of the propeller under open water conditions and in propulsion and cavitation tests
-    the steering moment and the horizontal thrust during manoeuvring tests.

SVA z-drive Z600/4 for measurements with podded drives.

The SVA driving and measuring systems comprise a vertical shaft and a mitre gear in a cylindrical gondola. The geometry of the thruster housing or pod is simulated with dummy housings.

Six component balance with mounted podded drive.

The numerical calculation of forces and moments gets difficult at larger steering angles as the inflow to the propeller, gondola and strut changes with the steering angle, causing flow separation. Model tests are then carried out to get a data basis for the forces and moments  under these conditions.  

The videos show examples of a turning  podded drive with pull propeller at cavitation identity. The propeller was blocked or rotated at different rates of revolution.