Pages 51-60
This paper describes the results of full scale speed trials as well as model experiments, with the propeller under various load conditions. These experiments were conducted with the intention of examining the model-ship correlations of self-propulsion factors, especially thrust deduction fraction. When the model-ship correlation in ship propulsion are considered, correlations of hull resistance and thrust deduction fraction cannot be directly examined because of the difficulty of ship resistance measurement. The authors tried to examine the behavior of thrust deduction fraction of full scale ships without measuring hull resistance, by means of varying the propeller load. Two sister ships were used for the experiments: 163,000 DWT type ore-oil carriers built at Innoshima Shipyard of Hitachi Shipbuilding & Engineering Co. Ltd. In addition to the ordinary speed trials, special trials were carried out with the ships towing sea-anchors on both sides. The sea-anchors gave additional resistance to the ships, and were very useful for varying the propeller load. A model of 9 m in L_<pp> was tested in Ship Research Institute, the Ministry of Transport. Self-propulsion tests of the model were conducted with various skin friction correction, corresponding to the conditions of the ship speed trials with sea-anchors. Comparing the results of the ship speed trials with those of the model experiments, the model-ship correlations of self-propulsion factors were examined in particular ways. Conclusions obtained are as follows, though further investigations may be necessary to be precise. (1) Results of the experiments differ from the general knowledge until now; the values of the self-propulsion factors, excepting (1-t) in the full load conditions, vary with the propeller load. (2) η_R rises with the increase of the drag (additional resistance to the ship). The η_R values of the ship seem to be the same as those of the model. (3) When the drag is increased at a constant speed, (1-w) increases in the full load condition while it decreases in the ballast condition. (4) Concerning (1-t), it seems that: a) In the full load condition, the vaiues of (1-t) remain constant regardless of the variation of the propeller load as usually believed. b) In the ballast condition, the values of (1-t) vary most irregularly in the self-propulsion factors, but have a general tendency that they decrease with the increase of the propeller load coefficient.
