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(Lauri Tarkkonen) wrote:

In "Lloyd Sumpter" writes:

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.

Fixed-blade prop:
This is the simplest and least expensive option. The blades are fixed
at a certain pitch. They also give the most drag under sail. To reduce
this, most sailing props are thinner, "high-aspect-ratio", and usually
have more advanced foil designs like "cupping" to increase drive in
forward. The downside of THIS is that in reverse, the advanced foil is
going through the water backwards, reducing effectiveness.

Examples: Michigan Wheel "Sailor" series and Campbell Sailor props.
Cost: around $500 CDN

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: ??

Looks like you have not learned much about props. Some fixed blade
props are very poor on reverse, especially if they are optimized to
give the best performance forward and some (good) folding props
are as good on reverse than forward and much better than some
fixed props on reverse. An example for you is the Danish Gori,
but there are others. The centrifugal force has no problem in
keeping the Gori open on reverse. There are some poor ones, but
why buy a poor one, as there are good ones available?

Feathering Prop:

Instead of the entire blade folding down under sail, they rotate,
("feathering") so that the leading edge is all that is presented. This
is not QUITE as low-drag as a folding prop, but far lower than a fixed
prop. When under power, the blade rotates to a fixed pitch angle. The
side benefit is that it rotates the opposite way to reverse, so the
leading edge is leading in both forward and reverse, meaning any
cupping or advanced foil design is used in both directions. Another
side benefit is that most props allow you to adjust the "fixed" pitch,
some easily enough that it can be done underwater, eliminating the
need to haulout to get that "perfect" pitch.

Examples: Maxprop and AutostreaM
Cost: About $2000 CDN

If you have a good three bladed propeller it can be much more
quiet while motoring than a two plade folding propeller and
can be worth the exstra cost.

In our boat at least, it isn't the prop that is noisy it is the shaft
that it is attached to. Sailing with a fixed prop sounds like you are
standing next to a very busy freeway (in addition to the loss of about
a knot of speed).

There are only two ways to stop our shaft from rotating underway -
having a feathering or folding prop is one. The other is immobilizing
the shaft with vice grips.

While that may not be true in other boats, in our particular boat with
our particular set up (which there are some 300 other boats with the
same setup) that's the way it is.

Auto-prop:

This is the same as a feathering prop, but instead of a fixed pitch,
the pitch varies with speed, torque, etc. similar to the "torque
convertor" on a ski-doo. This allows max power at all settings, best
fuel economy, fastest cruising and WOT speed, etc. The downside of
course is the cost.

You might not be able to recover the cost difference in the fuel
saving, especially if you are sailing a lot.

- Lauri Tarkkonen

Example: AutoProp (don't know of any others)
Cost: $3000 CDN

Lloyd Sumpter
"Far Cove" Catalina 36

grandma Rosalie

S/V RosalieAnn, Leonardtown, MD
CSY 44 WO #156
http://home.mindspring.com/~gmbeasley/id2.html