Stepped Surface Propeller
A marine surface propeller, and blade therefore, which is surface piercing and partially submerged, and includes a blade geometry that improves distribution of pressure and control to wetted and ventilated regions. Preferably, the feature has a positive step (ramp, cup, interceptor, indent or other geometric addition or intervention) between one fifth and four fifths chord length so as to create a high pressure peak or zone in what is now a low pressure zone on either the blade face or back or both and to create speed controllable wetted and ventilated regions.
1 . A propeller for a marine craft drive comprising a plurality of blades wherein each blade is securably attached to a central propeller hub, the propeller comprising:
a blade having:
a blade root securably attached to the propeller hub;
a blade tip distal to the blade root;
two major and opposing surfaces: a blade back and a blade face wherein the blade face is subjected to a higher pressure from a fluid than the blade back while moving forward;
two major and opposing edges: a tapered leading edge, and a trailing edge which is thicker than the leading edge;
a trailing edge step feature on the blade face and at about the trailing edge;
a second step feature on either the blade back or the blade face; wherein the blade face increases thrust up to 30% per area, versus a blade face without a step feature, when fully wetted.
2 . The propeller for a marine craft drive of claim 1 , wherein an efficiency of the propeller is increased at least 2% when fully wetted and increased at least 3% in a 50% face wetted mode.
3 . The propeller for a marine craft drive of claim 2 , wherein the increase in efficiency creates an additional thrust increase of at least 4% versus a blade face without a step feature.
4 . The propeller for a marine craft drive of claim 1 , wherein the trailing edge step feature is located in a range of 20% to 80% along the blade chord length of a pressure face of the propeller.
5 . The propeller for a marine craft drive of claim 1 , further comprising a height of the trailing edge step on the blade face of the propeller of 0.5% to 6% the chord length.