You seem to have it nailed, Lloyd. One comment: I know three guys who
went AutoProp in the last three years, and none of them liked the
price one bit, and all of them are ecstatic with the result and babble
on endlessly on how great they are.

I must admit, my friend with the original 1979 Volvo 35 hp on a
full-keel Wallstrom steel ketch of about 16 tons says that buying the
AutoProp meant a whole second lease on life for his engine, although
he suspects greater wear due to torque on his coupling and
transmission. He now goes hull speed (couldn't before), gets better
fuel economy, and docks like he's parallel parking a minivan. It's
quite impressive to see him "braking" to a full stop....this prop has
phenomenal bite.

They cost a lot because they are custom casting. You have to take
extensive geometry off the arse of the boat. Also, he cut away part of
his rudder (it's skeg-mounted) to take full advantage of the prop
swing.

Not everyone can or wants to do that, but not everyone has $15-20K for
a new diesel in the 50-75 HP range.

R.

On Thu, 23 Oct 2003 15:18:22 -0700, "Lloyd Sumpter"
wrote:

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: ??

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

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.

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

Lloyd Sumpter
"Far Cove" Catalina 36