Our products bring the many benefits of today’s technology to essential equipment that has undergone few modifications and improvements since Nathanael Herreshoff’s invention of the first folding propeller at the dawn of the twentieth century. The hydrodynamic properties of all propellers pose complex problems. These problems only worsen when it is necessary to reconcile the reduction of drag under sails and the search for maximum engine thrust on a boat characterized by relatively low engine power and high dunking.
The thrust depends on the surface of the propeller blades. There is no alternative.
To increase the thrust from a given power, it is necessary to increase the surface of the blades. The obvious solution to achieve this goal is to increase the number of blades for a given propeller diameter. In the absence of a simple and economical three-blade propeller, many have chosen to fall back on traditional fixed three-blade propellers. This solution allows them to obtain reasonable performance at the engine but at the cost of a huge deficit in performance under sail.
With a substantial increase in blade area, KIWIPROP’s three-bladed composite propellers provide significantly increased thrust. At the same time, they are freed from the well-known problems of corrosion, wear, weight, vibration and poor reverse performance inherent in traditional two-blade folding propellers. Kiwiprop has designed a feathered propeller that eliminates gears by using Zytel™, a patented DuPont composite, for the manufacture of injection molded blades.
Gear-feathered three-blade systems have long been the most capable propellers overall for sailboats. However, the significant problems inherent in their very design have been a hindrance to their diffusion especially for engines of less than 50 hp which represent the majority of the propeller market. In the first place, their price is high due to the complexity of the individual machining required to manufacture each propeller. The conical gear sprocket of each blade must be machined individually in addition to the hub gear.
Disadvantage much more penalizing for sailing under sail, but very often ignored, the blades remain parallel to the propeller shaft, not to the water nets which represents a significant drag and causes an autorotation of the tree under sail. Note that all diagrams depicting gear feathered propellers are made from the perspective of the shaft. They show a propeller with a very small projected area. This representation is very misleading because with a shaft inclined by 10 to 15 degrees and a rear slender line inclined by 5 to 10 degrees, the propeller receives the water nets at an angle of about 15 to 20 degrees.
This configuration generates a large projected area for each blade which results in drag and oscillation with all the correlative problems of noise, wear and decreased performance under sail. Any oscillation causes significant wear of the internal mechanisms for which maintaining effective lubrication is always a complex problem in the harsh conditions of the underwater environment.
Compared to competing models, it is necessary to add to the cost price of these propellers with gear feathering and not automatic an expensive system of locking the shaft and all the related problems. Not all different types of inverters can lock the rotation of the propeller shaft when the engine needs to be running to activate the internal clutch. By eliminating gear systems and using the Zytel’s™ neutral buoyancy, the KIWI FEATHER PROP propeller allows each blade to orient itself freely like a weather vane according to the water nets that actually run through it, regardless of the inclination of the propeller shaft, the drift or the movements of the sea. Thus, the drag and the phenomena of autorotation are reduced to the lowest levels.