It is a well known fact that the slow-rotating large-diameter propellers will be effective for improving the propeller efficiency. In the wake of such being popularly adopted, propeller's blade area ratio have been reduced gradually.

 With such a propeller, the pressure recovery on the trailing edge will be made rapid inevitably; whereby the water streams will be separated from the blade surface. Photo.3 shows the water streams over the propeller's blade. You can see the separation phenomenon at the conventional propeller's (CP) blade on the trailing edge for a wider range. With the water streams separation, the pressure distribution will be changed, and various adverse influences will be given on, for example, the propeller pitch in a sense of hydrodynamics, and others. It is the PAI propeller that was developed for solving such a problem.

　

　

　

　

 Fig.4 shows the pressure distributions over the blade for the PAI propeller and for CP in. The difference is seen in the slopes of the pressure distribution on the trailing edge. With PAI propeller there is a wider area of positive pressure over the pressure side, besides with non-existence of the negative pressure peak on the leading edge. It could accordingly be said that PAI propeller has solved the problem of separation of water streams which has been an inevitable unfavourable phenomenon characteristic of smaller blade area propellers pursuing the improvement of the efficiency, furthermore it has been devised for the improvement of anti-cavitation characteristics. As explained, PAI propeller is the propeller made suitable for smaller blade area ratio promoting the improvement of efficiency, by applying the improvements in accordance with the pressure distribution preferable. From such a background of the propeller, it is named PAI (Pressure-Accorded Improvement) propeller. Fig.5 shows open propeller efficiency curves for MAU propeller and PAI propeller. PAI propeller's is higher nearly as much as 6% over the MAU propeller's. Generally speaking, the value of the efficiency improvement will be around 4% over the MAU propeller to be obtained from its designing diagram.