We took a three blade Max-Prop around the world on Swee****er and I
would never use anything else for serious cruising. Low drag,
excellent thrust in forward and reverse (you really care about thrust
in reverse when maneuvering in a tight marina), can be adjusted to
exact required pitch.

On the other hand, the boat I race on uses a folding prop. The key
there is absolutely the lowest possible drag -- nothing else matters
-- and only a folding prop will do it. The fact that it's kind of
anemic going forward and even worse going backwards, and that you have
to set it with the hinge horizontal when you shut off the engine, are
secondary to the lowest possible drag. For a serious race boat, I
would have nothing else, but I see no other use for one.

The standard sailing propeller used to be a two blade with relatively
low blade width that would hide behind the keel of the typical long
keel boat. Now, with virtually all sailboat propellers out in the
open, I wouldn't want a fixed prop under any circumstances -- it's
just a big drag.

As for AutoProp, it sounds like snake oil to me, and unecessary to
boot. The propeller law curve drops off at roughly the third root of
RPM
ie, HP ~=~ RPM^0.3333). Once you throttle back a little, the HP goes
down very fast, almost always a little faster than the engine's
ability to produce HP. This protects the engine beautifully -- choose
a prop to absorb the HP produced at max revs and you know you have
enough HP at all lower revs. Why mess with Mother Nature when she's
making life easy?

And on our current love? 59"x39" three blade cast iron.

Jim Woodward
www.mvFintry.com



"Matt/Meribeth Pedersen" wrote in message link.net...
"Lloyd Sumpter" wrote in message
news
Hi,
After the "What prop should I use", I've done some research and thougth
I'd post what I've learned about various props.


Folding Prop:
This is the ultimate sailing-compromise prop. Under sail, the blades fold
down to become hardly more than a giant "teardrop" on the end of the
shaft, giving virtually no drag. Under power, the rotation pushes the
blades out, and the backward force pushes the blades out
completely. The downside of this is that in reverse, the force is
trying to FOLD the blades, and centrifugal force is all that's keeping
them out. This means VERY poor performance under power in reverse.

Examples...?
Cost: ??

I think Martec has their prices on their web site. I have a 27'er
and the 12 x 10 folding prop I need is about US$550. Gori was
in the same price range, if you're willing to bargain. Both these
companies make geared props, where there is an intermediate
gear between the blades that forces them to open at the same rate.
This keeps vibration to a minimum.

In general I agree that folders don't function as well in
reverse as a fixed, but if you just increase engine RPMs
you can get the thrust you need for most situations.