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.

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

x-no-archive:yes
(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

Lauri Tarkkonen wrote:

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

Lloyd mentioned that.

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?


When I looked for a feathering/folding prop, I'd never met anyone with a
folding prop that could depend upon the blades opening fully in reverse
every time, particularly in an emergency; they all seemed to have to
baby them and learn tricks. I also wondered whether the more modern
transmission gearings make it worse: Our 2GM swings at a maximum of 1200
rpm, quite a bit slower than the anemic engine it replaced.

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.


We had to replace our fixed two blade because of harmonic vibrations at
high power. The whole boat shook, which can't have been a good thing.
The 3-blade is MUCH quieter and smoother; not quite as efficient, but
not as bad as I expected.

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.


Overall cost savings don't much enter into this sort of purchase.
Cheapest by far would be a fixed prop. It would take us a very long time
to consume $1500 worth of fuel, much less save that much on fuel. (In
1067 hours, we consumed 341 gallons.)

If you want to save $$, slow down. We normally power at 5.7+/- knots and
consume 0.36 gph. That's not an unreasonable speed with our 6.6 knot
hull speed. When we went 6.2+/- (enjoying the new prop), consumption was
0.69. When I backed off to 5 knots for a month, consumption over 43
hours was 0.20. To gain just over a knot, we used 3.5 times as much fuel.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

On Sat, 25 Oct 2003 18:07:58 +0000, Jere Lull wrote:

Lauri Tarkkonen wrote:

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

Lloyd mentioned that.


Of course all the data I have is theoretical - YMMV. The "testimonials" I
read about how much better even some fixed-blade props were in reverse
against folding props were written by folks who replaced their folding
props - so obviously they were not happy with them, or at least felt they
had to justify their decision.


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.


We had to replace our fixed two blade because of harmonic vibrations at
high power. The whole boat shook, which can't have been a good thing.
The 3-blade is MUCH quieter and smoother; not quite as efficient, but
not as bad as I expected.


I will never go back to a 2-blade, period. A writeup at WestByNorth tells
why: http://www.westbynorth.com/choose.htm


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.


Overall cost savings don't much enter into this sort of purchase.
Cheapest by far would be a fixed prop. It would take us a very long time
to consume $1500 worth of fuel, much less save that much on fuel. (In
1067 hours, we consumed 341 gallons.)


Agreed!
I can see some non-monetary reasons for going to a feathering or folding
prop, but can't see the advantage of the auto-prop.

I'm now torn between the 3-blade fixed Campbell Sailor and the AutostreaM.
I like the AutostreaM's stainless-steel: at the very least, it would Look
Kewl on my SS shaft (and I know the corrosion and marine-growth
characteristics of SS). I also like the ability to change pitch - I now
feel that PITCH is the primary variable to get optimum power/speed from
the prop. I suspect that a C.S. fixed would give marginally better
performance than an AutostreaM AT OPTIMUM PITCH. But since the A-S is
easily adjustable, I think I'd be able to achive optimum pitch much faster
and more easily.

I'd also like the feathering advantage, although I was jokingly adding up
all the "fasters" I could get: feathering gets me 1-2 knots faster, the
Sail Guy said a new headsail would get me at least a knot, clean bottom
would give me an extra 1/2 to 1 knot...and I was going 6 knots in an 8
knot breeze. So add that all up, and I'd be going about 9-10 knots!

Lloyd Sumpter
"Far Cove" Catalina 36

Lloyd Sumpter wrote:

On Sat, 25 Oct 2003 18:07:58 +0000, Jere Lull wrote:


Overall cost savings don't much enter into this sort of purchase.
Cheapest by far would be a fixed prop. It would take us a very long time
to consume $1500 worth of fuel, much less save that much on fuel. (In
1067 hours, we consumed 341 gallons.)

Agreed!
I can see some non-monetary reasons for going to a feathering or folding
prop, but can't see the advantage of the auto-prop.


The AutoProp's an unusual beast. After some discussions this past
season, I might consider an AutoProp for a trawler or other
mostly-powered boat: the blades keep a constant *relative* pitch, giving
better thrust and keeping the engine better loaded at reduced RPMs.

I'm now torn between the 3-blade fixed Campbell Sailor and the AutostreaM.
I like the AutostreaM's stainless-steel:

I like the *idea* of SS as well, but our SS shaft gets considerably more
growth than the bronze blade, even at the hub. And bronze seems more
suited to hard knocks. I've been thinking of switching back to a bronze
shaft....

I'd also like the feathering advantage, although I was jokingly adding up
all the "fasters" I could get: feathering gets me 1-2 knots faster, the
Sail Guy said a new headsail would get me at least a knot, clean bottom
would give me an extra 1/2 to 1 knot...and I was going 6 knots in an 8
knot breeze. So add that all up, and I'd be going about 9-10 knots!


They apply at different speeds. Once the wind's up and you're pressing
against hull speed, you're wasting power intentionally. I honestly have
noticed the speed bump up a half to full knot when I locked the blades
at 4-5 knots. The bottom makes the most difference at lower speeds, as
can the sail. Adding all of the effects together can make the difference
between 2-3 knots and not being able to move at all. THAT can surprise
neighboring boats.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/