Unlike a bronze propeller a well designed plastic prop will flex under load adding pitch in reverse and sometimes loosing pitch in forward. The improvement in reverse over forward can be from the flexing of the plastic propeller blades adding pitch to the prop in reverse.
The nest time you have the prop close to hand try flexing the blade tip. if it moves even a little bit it will be gaining and loosing pitch under load.
larry
--- In electricboats@
>
> I now have one of the so called 'speed' props from Torqeedo, and if
> you are considering a Cruise 4, this prop is worthwhile.
>
> But not for the reason you might expect...
>
> First some background. The Australian Torqeedo distributor, Claude
> Desjardins, has provided me a 'speed prop' for testing on Current
> Sunshine. I understand it was designed for use on light planing hulls
> with a view to getting more top speed for them than the standard prop.
>
> Oddly enough it seems to make little difference to speed - and if
> anything is perhaps a little slower for top speed. Since I've had it
> I have not had the opportunity to test it under still conditions and
> so my tests so far have all been effected by wind. And even just a
> slight breeze can effect the results by .1 or .2 of a knot either
> way. Anyway, the top speed is still around about 6.5 knots.
>
> But what I really notice is its power in reverse. It way better than
> the standard prop. Many times better. And this big improvement in
> reverse is also confirmed by a friend who has two Cruise 4 on his Oram
> 45ft cat. He also notices very little change in speed, but a big
> improvement in reverse.
>
> The standard prop is orange and has very fine blades - the speed prop
> is white and its blades have more area especially towards the tips.
> So this is perhaps why it shows such an improvement in reverse. But I
> expect there are alos other more subtle shape changes as well that are
> helping here.
>
> Reverse on the standard prop can be really unsettling on any boat with
> substantial mass - and this would apply particularly to the sailboats
> of this group. For the original design target for these outboards,
> the small dinghy, reverse is not so important.
>
> But for sailboats manoeuvring in close quarters it can be critical.
>
> If you are thinking of getting a Torqeedo be sure to ask about the
> speed prop.
>
> Cheers
>
> Chris
>
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