Molland, A.F. and Turnock, S.R.
Flow straightening effects on a ship rudder due to upstream propeller and hull
International Shipbuilding Progress, 49, (3), .
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A description is given of an investigation into the flow straightening effects on a ship rudder of an upstram propeller and hull. In order to quantify these effects an experimental investigation was carried out using a 3.5 m x 2.5 m wind tunnel. The tests were carried out with an all-movable rudder and a representative propeller for drift angles up to ±15°.
Three different lengths of centreboards were tested upstream of the rudder-propeller combination, together with a representative hull. Flow straightening effects were found to be dependent on the type of upstream body, drift angle and propeller thrust loading. The effects of the three centreboards upstream of the propeller were found to be significantly greater than the effect of the propeller on its own. The straightening effects of the hull were found to be less than those for the centreline boards. There was an increase in flow straightening with increase in propeller thrust loading at a drift angle of 15° but at 7.5° drift this effect was less apparent and sometimes reversed.
The overall results provide a better understanding of flow straightening effects and data for improving the prediction of manoeuvring rudder forces. The data for the centreline boards are likely to have applications for vessels with a relatively thin upstream skeg, whilst the data for the rudder plus propeller combination in isolation should be suitable for vessels with open water sterns, such as twin screw vessels.
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