Mitsubishi Experimental Tank has been noticing the unstable phenomenon sometimes observed in the self-propulsion test of full ship models and endeavoring to make clear this phenomenon since several years ago.
It was found recently that the velocity field at stern of such a model showing the unstable phenomenon varies distinctively with the action of propeller.
The velocity field at stern of such a model in the case of self-propulsion test is remarkably influenced by the propeller loading and it tends to the velocity field in the case of resistance test as the propeller loading is decreased to zero.
It is not clear yet whether such a phenomenon exists on an actual ship as well. However, from another study made by Mitsubishi Experimental Tank, it is probable that the phenomenon is peculiar to model due to insufficient Reynolds number, even if a seven meter model is used. Then the meaning of model test becomes questionable and the study on ship-model correlation becomes to be burdened with another difficulty.
In order to design a superior ship form in such circumstances, it is the wisest way to have as many reliable data as possible on the ship-model correlation of full big ships and to advance the study of better ship forms recognizing the existence of such an unstable phenomenon.