Space available to fit the propeller is somewhat limited by design. Without modification to the hull it will be difficult to fit anything bigger than a 17“ propeller, usually about the minimum for gear box ratios available to the market today. This will provide not more free space than some 1“ max between the tip of the propeller blades and the hull.

We and others have chosen a 3-blade 17“ MAX-PROP. This propeller is ideal when changing from the VOLVO PENTA B-series engines originally installed to newer engines-types. The MAX-PROPp can be adjusted to work both directions. The VOLVO B-series engines were often fitted with the so called RB-gear box which made the propeller spin in the same direction as the engine crank-shaft, ie opposite compared to today’s gear-boxes (the RB gear box was direct-driven). Given the rather small aperture for the propeller to spin it might be sensible to stick to engines up to 30 HP to be able to fit the right propeller but to avoid bigger engines as it will be difficult to transmit the added HP into the water.

Here you can see how the water-cooled cutlass bearing is replaced and a new Max-Prop propeller is fitted on John Martin of Rye. Please check the drawings describing details of the propeller shaft mounting in the Drawing and Plan section of this website. It is recommended to have the water-cooled bearing protruding some 1/2“ out of the hull to allow for increased cooling of the shaft and bearing. Ignoring this has resulted in very short life span of the bearing on some boats.

Fitted with Max-Prop
We know of two propellers that can be used: Again space for them is limited and therefore a propeller should be chosen where the mechanics are arranged in close proximity to the conus as otherwise the space for the propeller to spin freely may become restricted. TYNAJE (US 2222) has a MARTEC 2-blade folding prop which will be about the only folding prop to be fitted. It is available from MARTEC in California/USA.

Photos Courtesy of boat owner