In the project NOVIMAR the interaction between a leading and a following inland waterway vessel was investigated with model tests at DST. The main objective was to understand the hydrodynamic ship – ship interaction between the vessels travelling at small longitudinal distances and different transversal offsets. As a result the changes in required power for both ships could be determined. The resulting side forces and yaw moment of the follower were also recorded.
For this purpose, two models with identical bow shape but different aft bodies were used, both are of typical motor vessel size. The measurement results show that, as expected, the following ship in close proximity to the leading ship does not experience a positive influence on the power demand. In the overall view, this initially negative effect is partly compensated by positive effects on the power requirements of the leader. Contrary to previous assumptions, these effects are not caused by the influence of the propeller thrust, but by the wave pattern. The stern of the leading ship is practically raised by the bow wave of the following ship.
Even if the power requirement of the vessel train as a whole is only slightly higher than the sum of the individual vessels, it must be kept in mind that the increase in power due to rudder operations to keep the course has not yet been taken into account. These will have an additional negative impact on the overall power requirement. While the power requirement of the follower decreases with increasing distance, the lateral forces continue to act on the following ship. These hydrodynamic disturbances of the leading ship will still have an effect on the course keeping performance of the following ship at a greater distance.
For a more detailed investigation of the hydrodynamic effects, further model tests focusing on the flow between the ships are necessary. PIV investigations are planned for this purpose in the future.