Underpowered, which propeller to install?

[malbert73]

Originally Posted by Jim Cate

The prop on this boat is a Flex-O-Fold three blade, and this is not a feathering prop, but the best of the folding prop offerings. On our previous boat we had an AutoStream feathering prop, made here in Oz, and IMO, a better bit of kit than the Max Prop, and at a considerably smaller price (when we bought it in ~ 1998). Dunno about now.

When considering feathering props, one needs to factor in their lower efficiency than other prop types, due to the flat, non-twisted blade shape and in the smaller diameters, the relatively large hub diameter which limits blade size. There have been numerous threads on this subject here on CF, and if one looks at actual data instead of personal opinions, the F-O-F actually outperforms the Max prop except for static thrust in reverse. Whether this, or any prop will help the OP's situation is beyond my pay grade, but if I was worried about lack of power I'd not be willing to take the efficiency loss associated with a feathering prop of any manufacture.

Jim

+1 on that. Compared to feathering, flexofold has much better forward thrust, reduced drag (and less chance of snagging lines), and much worse reverse. I am willing to take reduced reverse for better other domains.

[bongo]

We've had a Kiwi Prop for more than 5 years with no problems. Smooth, SIMPLE, reliable. I adjusted the pitch for a good curising speed at a lower RPM, and this can be done while it is in the water. The only downside I see is that barnicles love the composite blades. If you don't use the boat for several months in the summer, scrape the blades before you cast off.

[GALAWA]

If your boat is underpowered, and if you are concerned by propwalk, you should definitely consider an AUTOPROP.

The baldes of the AUTOPROP are properly twisted and rotate automatically so that their pitch relative to the flow of water, as opposed to pitch relative to the shaft, is constant.
When powering at slow speed against wind and see, the pitch is reduced automatically enabling the motor to reach maximum RPM and power. This is particularly usefull if your boat is underpowered.
When motorsailing, the pitch is encreased automatically, generating usefull thrust, even at low RPM.
When powering astern, the blades rotate completely so that the leading edge is set properly, and the blades reduce their pitch enabling high RPM and affording a rearward thrust unmatched by any other prop.

This thrust performance is unmatched by any other prop, notably not by MAXPROP's flat blades.

Finally the main cause of propwalk is the fact that
In reverse, with a fixed prop, the blades of which are properly twisted, the blades are used upside down, trailing edge forward, convex side used as intrados, concave side used as extratos. They throw more water radially and this water hits the hull assymetrically above the prop ( and thrust much less)

With regard to the water thrown radially causing propwalk, the flat symmetrical blades of MAXPROPs , and the rotating blades of the AUTOPROP perform equally well. But the reverse thrust of the AUTOPROP is far greater.