An economic propeller choice for narrowboats

The Vetus 3-bladed propeller, measuring 19” in diameter with a 14” pitch, is a relatively large propeller, but no problem for the hi torque Törkmar motor. Made from manganese bronze, it offers excellent value and reliable performance, making it a very good propeller for the money.

Understanding Propeller Specifications

The term Fa/F = 0.52 refers to the propeller’s disk area ratio. This is the total blade area divided by the total area of the circle swept by the propeller tips. A value of 0.52 indicates a relatively low blade surface area, which is a characteristic of propellers designed for lower speeds, common for inland waterways. This low ratio contributes to the propeller being less taxing on the engine. The 1:10 taper on the propeller hub is a standard way of describing how the shaft narrows. For every 10mm of length, the shaft diameter decreases by 1mm, ensuring a secure fit on a tapered shaft.

Shaft Recommendation

A 35 mm shaft is recommended for this propeller to ensure it can handle the torque and thrust generated. Using a shaft of this diameter provides the necessary strength and stability, preventing issues like bending or excessive vibration. The combination of a strong shaft and the propeller’s material and design ensures a durable and efficient propulsion system that is a great investment for many narrowboat owners.