Feathering sailboat propellers tackle the compromise of a sailboat propeller in a very specific way. Unlike folding sailboat propellers such as Varifold which swing the blades out of the flow and behind the propeller hub, the feathering sailboat propeller blades rotate the blades in the flow to a no-lift condition when sailing, commonly called feathering. To do this the propeller has to have flat blades that are symmetric and are in effect, like a paddle. This allows the feathering propeller blade to be low drag. However the very concept that reduces the drag for this propeller also limits the propeller as an efficient generator of thrust when the engine is in use.
Independent tests have shown that at a cruising rpm flat blade propellers produce very low thrust and therefore the boat speed produced is very low, even lower than a standard fixed propeller. In addition the feathering propellers are notoriously noisy and prone to vibration. This effect is again related to the flat paddle like blades not being optimized for the flow that they operate in.
Also the propellers typically have a large blade area exposed to the water flow, which increases drag. This drag is even greater when the shaft is angled downwards. At higher sailing speeds the feathering propeller will begin to auto-rotate. If the engine is in gear, the propeller can cause the engine to turn over and this would create water problems within the engine so they require a shaft lock .
However not all feathering designs have this limitation of flat symmetric blades. The Autoprop blade however, has true camber and profiled shape (airfoil) to each blade. Therefore the thrust developed is greater than a flat blade. This is especially true at the cruising rpm or in adverse condition such as motoring into a head sea. The efficiency is higher than that of a fixed propeller by over 10%.
The Autoprop is a feathering propeller. As the blades align themselves to the water flow when under sail they feather to the water flow, not the shaft angle. Tests have shown that the Autoprop has the lowest drag of all three bladed feathering propellers and 85% less than a fixed propeller. Other feathering propellers have only one pitch setting under power. Autoprop has countless pitch settings, its fully automatic. Motor-sailing is vastly improved and greater thrust at lower rpm and in creased speed. Less engine rpm results in lower wear and tear, less noise and vibration, increased fuel economy and a greater cruising range.
To meet the many installation options the Autoprop propellers are available in a combination of 2 and 3 blade propellers suitable for shaft and sail drive in a wide range of diameters.