12A full understanding of the hydrodynamic processes within the jet produced by a manoeuvring 69fully understood if an engineer is to be able to quantify any scouring damage that may occur, 70and, more importantly, size protection systems to be deployed to prevent further damage. 72The flow field produced by the action of rotating propeller blades is complex in nature. Near 73to the propeller, the passing blades and rotating hub influence the characteristics of the flow. 74As the jet diffuses downstream, the velocity characteristics become similar to a submerged 102The propellers used in this investigation varied in size (Dp), numbers of blades (N), pitch to 103 diameter ratios (P'), thrust coefficients (Ct), rake and blade area ratios (β), as shown in Table 104 1. The number of propeller blades varied from three to six. The pitch to diameter ratio ranged 107The blades of propeller 1, 3 and 4 had no forward inclination i. Equation 3 124 125The rotational speeds used in the programme of work were based on standard Froudian scale 134The propellers were operated across a range of speeds that bounded these target values, 135and these are listed in full in Table 2. 137The Reynolds numbers for the propellers operating at these rotational speeds ranged from 138

Determining the efflux velocity in a ship's propeller jet is the key to calculating the velocity at any other location within the diffusing jet. Current semi-empirical equations used to calculate the magnitude of the efflux velocity have been based on studies that employed a limited range of propeller characteristics. This paper reports on the findings of an experimental investigation into the magnitude of the efflux velocities of the jets produced by four different propellers, where the characteristic of the blade geometry has been chosen to extend the range of applicability of the outcomes. Measurements of velocity have been made using a three-dimensional laser Doppler anemometry system, with the test propellers operating at a range of rotational speeds that bound typical operational values.Comparisons are made with current predictive theories and, to aid engineers in the design of marine infrastructure, methods are presented by which the three-dimensional efflux velocity components, as well as the resultant efflux value, can be more accurately determined.

Bellaghy, Co. Derry. Northern Ireland ε gradient coefficient defined in Equation 3 ν kinematic viscosity of fluid (m 2 /s) 62 Maritime Engineering Volume 168 Issue MA2 Three-dimension efflux velocity characteristics of marine propeller jets Hamill, Kee and Ryan