This paper addresses effect of the Reynolds number on the optimum diameter and optimum efficiency of propellers with laminar flow blade section (N propellers) in comparison with those of MAU propellers.

A series of propeller open water tests (POT) were performed at a high Reynolds number by using N4-50 propellers (number of blades 4, expanded area ratio 0.50), of which results show that the optimum diameter and optimum efficiency of N propellers are respectively 2～5% larger and 5～7% higher than those of MAU propeller design charts. The effect of different Reynolds number is included in these differences. Considering the effect of different Reynolds number between POT of N propellers and MAU propeller design charts, it may be said that the optimum diameter and optimum efficiency of N propellers are respectively almost same as and 2～3% higher than those of MAU propellers.

Next, CFD calculations were performed on open water characteristics of N4-50 propellers at model and full scale conditions, of which results show that the optimum diameter and optimum efficiency of N propellers are respectively 0～1.5% larger and about 1% higher at the full scale condition than at the model scale condition.

Finally, it is confirmed that 5% diameter deviation from the optimum diameter leads to about 1% efficiency down and the efficiency down is not almost affected by the propeller type nor the Reynolds number in case of small deviation from the optimum diameter.