Propeller Inflow at Full Scale During a Manoeuvre

The propeller inflow of a patrol boat of the Australian Navy was measured at full scale using a newly developed LDV technique. The velocity distribution in front of the propeller was measured, both on a straight course and in a turn. Model tests that were carried out in a towing tank with the model at a drift angle were shown to adequately simulate the most important effects of the wake distribution. The model wake data were used to complete the full scale data and an analysis was made of the power absorption of the propellers in relation to the inflow velocities.

It was found that the transverse velocities in the propeller plane were almost fully responsible for changes in power absorption in a turn. The mean axial velocity was about equal for the inner and the outer propeller in a turn. Unexpectedly the transverse velocities induced by a turn were small in the upper half of the propeller plane. The effects of the inflow measurements on the cavitation inception speed have also been estimated analytically.