Kiwi Feather Propeller

[jfoster]

I ran across an interesting feathering prop concept with allegedly much lower drag. http://www.kiwiprops.co.nz/ Their argument is:

Traditionally feathering props have blades geared together, to ensure that they line up with the shaft when feathered. However the shaft rarely lines up with the water flow, thus increasing projected area and thus drag. With a typical inboard engine the shaft will be angled down at 10 to 15 degrees and with the hull sloping up at say 5 to 10 degrees, the shaft may be 15 to 25 degrees off the streamline of the water flow. This can cause auto-rotation and wear with the need for shaft locks. In addition there can be 5 to 10 degrees of leeway on the wind and surging sideways in big waves.

In the Kiwiprop™ the individual blades are always free to "weather vane" in the actual water flow, to a minimum drag position so don't cause autorotation

Anybody know if this would be significant for longpac or transpac boats?

 

[tiger beetle]

Anybody know if this would be significant for longpac or transpac boats?

I don't know about the significance of drag relative to speed of the boat; I have a two blade martec and it will have less drag than any 3 blade prop (assuming I get the alignment right and have the monel hinge pin set vertically behind the shaft strut). I suspect that having up the wrong sail, or sailing on the wrong gybe, will have much more impact on finishing time than dragging a MaxProp vs. a Kiwiprop would have.

That said, the Kiwiprop looks like a great thing for long distance cruising witha 3 blade prop, as the blades are replaceable with the boat in the water. This is much simpler than carrying around a backup propeller (unless the prop is a Michigan). Critters growing on the plastic blades are problematic, so will require regular cleaning. Given the prop is roughly 1/3 the price of a bronze MaxProp, I will have to think seriously about this prop for my boat. I've been saving up for a 3 blade MaxProp, and the Kiwi prop looks likes it might give Max a run for their money.

I do not know the longevity of the prop. The Martic 2 blade elliptical folding is good for 7-10 years, and then it needs to be rebuilt; another 7-10 years and it's time to replace. I expect MaxProp to have about the same wear rate, and the plastic on the Kiwiprop may wear faster than the bronze on the Martec & MaxProp.

This might of of interest to you - Sailing Anarchy forum regarding the kiwi prop. People seem to like them a lot.

http://forums.sailinganarchy.com/index.php?showtopic=69891&hl=kiwiprop

- rob/beetle