rhys, hate to tell you this, but an Auto-Prop doesn't feather.

Still, the clown spent $3,500 Cdn, so you gotta expect him to tell you
*something*.

20 miles a day is a 15% improvement on a base 5.6 knot cruising speed
and you are correct that folding props make the most difference in light
air.

Reducing drag has the advantage over adding sail area in that it does
not add to heeling moment.

BTW, Gori, Martec, Brunton/Varifold and others make 3 blade folders.
Volvo even makes a 4 bladed folder.

Now, you can continue to rant and make an ass of yourself as usual but
that is all I have to say about it.

For what it's worth:

Buddy of mine with a steel Wallstrom-designed (partner to Brewer) 1979
ketch popped for a three-bladed AutoProp, a feathering design. He had
to haul out for many reasons: 1) to confirm the exact geometry of his
hull around the shaft; 2) to cut back his rudder at that point for the
install; and 3) to get the prop itself on. 1) was because it's
essentially a custom casting, and NOT cheap (about $3,500 Cdn.).

After three seasons now, he's happy as a clam with his decision and
outlay. He says the following:

Advantages:

Bigger prop, better bite and power curve. He's got a 35 HP Volvo
(probably 15-25 HP too small for a 28,000 lb. boat), but according to
him, the power he transmits to the prop is greatly increased. His top
speed without redlining has gone from 6.5 to 8.2 knots, or
approximately hull speed.

He says he gains 1/2 knot due to the self-feathering action, a
significant gain in typical light Lake Ontario air for this
essentially blue-water cruiser.

He backs down (after a quick rev to feather out the blades) far more
effectively now. He stops far more rapidly.

His docking is far more controlled. He can move his heavy, trad.
keeled boat like a minivan now. It's quite interesting to see.

Disadvantages:

The cones in his transmission have been wearing far more quickly and
have required replacement. He can handle this himself as a repair, so
it's more an annoyance than a tragedy, and spares from Volvo are
pricey.

He figures that shifting the gears with a bigger, heavier prop is
causing wear and tear beyond the engine spec. You can hear the "clunk"
of his shifting outside the boat, actually. He is consulting with a
marine engineer to determine a better course of action, but he is
leaning towards a shock-absorbing coupler and a thrust bearing
designed to isolate the engine transmission more effectively from the
sheer inertia of this otherwise fine prop.

Overall, he is so happy with the performance, however, both under sail
and power, that he would consider getting a new diesel to make full
use of the prop, rather than sticking with the small but still viable
diesel that perhaps doesn't have the beef at the back end to cope with
God's Own Feathering Prop G.

Hope this little tale helps.

R.

On 30 Aug 2004 03:34:57 GMT,
JAXAshby wrote:
rhys, hate to tell you this, but an Auto-Prop doesn't feather.



The blades rotate until they are inline with the shaft axis, how is this
not feathering?

Still, the clown spent $3,500 Cdn, so you gotta expect him to tell you
*something*.



What would have done the job as well, for less money?



--
Jim Richardson http://www.eskimo.com/~warlock
'Windows' really does make a fine swear word, representing all that's
taboo and awful - just like '****', '****', etc."
-- Mark Hughes, sdm

The blades rotate until they are inline with the shaft axis, how is this
not feathering?

take a look at the blades. they rotate and thus *reduce* drag, but they
certainly don't "feather".

(JAXAshby) wrote:

The blades rotate until they are inline with the shaft axis, how is this
not feathering?

take a look at the blades. they rotate and thus *reduce* drag, but they
certainly don't "feather".

Blades can be set to in-line with the keel (two blade props), but the
prop still has the blades at about 90 degrees to the shaft. For two
blade props on boats where there is something of the keel sticking
down into the water past where the prop is (like on many sailboats),
this does reduce drag. I think however that many sailboats don't have
two blade props and this doesn't work well with a 3 or more blade
prop.

In feathering and/or folding (since I know there is a difference but
don't remember what it is), the blades move to align themselves along
the shaft - kind of like furling an umbrella.

Some props can be folded or have the pitch changed from inside the
boat and some you have to either haul or go into the water. I think
that is variable pitch. A fixed prop where everything is one solid
piece is a non-feathering/folding and constant pitch prop.


grandma Rosalie

There seems to be a bit of confusion here. There are basically 4
different types of props with movable blades. All can improve sailing
performance to one degree or another.

Folding props: Blades with a fixed pitch are pivoted along the axis of
the shaft so that they fold back in the fore and aft direction. Blades
may be geared together or independent. In forward they are held open by
the forward thrust. Most have some camber so they are close to the
efficiency of fixed blades in forward but in reverse they are held open
by centrifugal force which means that you have to apply more power to
get them to perform in reverse. Folding props are preferred when sail
performance take preference over powered performance.

Feathering props: Blades are pivoted (more or less) perpendicular to the
shaft. They remain extended when idle but align themselves with the
flow to present the smallest cross section. The blades are geared to
the shaft so that they are held open by the torque. Pitch can be
adjusted by modifying the stops. In reverse the torque flips the blade
over so that you get the same pitch (and performance) in forward and
reverse. However, to achieve the lowest drag the blades usually do not
have any camber making them slightly less efficient. Feathering props
are preferred where a balance must be struck between sail and powered
performance.

Variable Pitch Props: Blades are assembled similar to feathering props
but are geared to a control shaft concentric to the drive shaft. By
adjusting the position of the control shaft relative to the drive shaft
from inside the hull the pitch can be varied to meet current conditions.
Usually the blades are cambered to optimize forward performance.
Variable pitch props are preferred where maximum performance under power
in all conditions is desired and cost is not a limiting factor.

Auto-Prop: Blades are pivoted similar to feathering props but are
independent of each other and can rotate a full 360º. The offset
geometry of each blade is designed to find its own most efficient pitch
by balancing torque against water pressure. Auto-Props can give close
to optimum performance in most conditions in forward or reverse. They
are not truly feathering however. With no torque water pressure forces
the blades back slightly which results in considerably more drag than
normal feathering props. Also they have considerably more mass which
puts a lot of strain on the drive train when shifting from forward to
reverse and back. If left idle for any length of time they require
considerably more maintenance than the others to keep the blades
rotating freely. Auto-Props are best where powered performance takes
precedence over sailing performance.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

On Mon, 30 Aug 2004 09:39:46 -0400, Glenn Ashmore
wrote:

Auto-Prop: Blades are pivoted similar to feathering props but are
independent of each other and can rotate a full 360º. The offset
geometry of each blade is designed to find its own most efficient pitch
by balancing torque against water pressure. Auto-Props can give close
to optimum performance in most conditions in forward or reverse. They
are not truly feathering however.

They are close enough in function to use the term constructively. I
don't think Autoprop's self-description of their product as a
"feathering prop" constitutes trade fraud in this instance.


With no torque water pressure forces
the blades back slightly which results in considerably more drag than
normal feathering props. Also they have considerably more mass which
puts a lot of strain on the drive train when shifting from forward to
reverse and back.

Agreed. As noted, my friend accepts the wear as adequate pay-off for
the motoring performance enhancements he was seeking. I wouldn't put
an Autoprop on a J-Boat, for instance, or any racer-cruiser. It's a
good compromise if you understand the pros and cons, not a universal
panacea for prop drag.

If left idle for any length of time they require
considerably more maintenance than the others to keep the blades
rotating freely.

He hauls in a TraveLift once a year (luckily his club possesses one)
and inspects and adjusts then as part of his general yearly hull
maintenance/cleaning/repainting. He says it's pretty straightforward
so far, but he acknowledges that they are complex pieces of machinery
for props.


Auto-Props are best where powered performance takes
precedence over sailing performance.

Debatable, if you consider the alternative as being a fixed prop or a
folding prop. I think you have to consider hull type, displacement and
engine output along with intended use. My friend takes his large steel
ketch out alone a great deal, and while he is fine sailing it solo, he
appreciates the degree of control his Autoprop gives him in tight
situations and in solo docking. Certainly that aspect--the degree of
control of a 15 ton boat-- is quite noticeable and is obviously worth
it to him in his use of a heavy displacement cruiser.

That's why I tried to give both pros and cons, as the Autoprop isn't
particularly well-known, being British. Getting one personally would
be senseless for my current boat, but seems a good compromise for him
and has bought him a few more years out of his 35 HP Volvo, even if he
has to rethink transmission isolation and so on.

But it's not for everyone. No "marine solution" is, except maybe for
those wooden tapered plugs people hang off seacocks. G

R.

On 30 Aug 2004 11:58:56 GMT,
JAXAshby wrote:
The blades rotate until they are inline with the shaft axis, how is this
not feathering?

take a look at the blades. they rotate and thus *reduce* drag, but they
certainly don't "feather".




I have, the blades rotate to line up with the axis of the shaft, how is
that *not* feathering?

--
Jim Richardson http://www.eskimo.com/~warlock
If Bill Gates had a nickel for every time Windows crashed... Oh wait, he does

the blades are curved, and rather dramatically so.



The blades rotate until they are inline with the shaft axis, how is this
not feathering?

take a look at the blades. they rotate and thus *reduce* drag, but they
certainly don't "feather".




I have, the blades rotate to line up with the axis of the shaft, how is
that *not* feathering?

--
Jim Richardson http://www.eskimo.com/~warlock
If Bill Gates had a nickel for every time Windows crashed... Oh wait, he does

So,Doodles, what you are saying, is that unless the blades are totally
flat, the term "feathering" can not be used?

otn

JAXAshby wrote:
the blades are curved, and rather dramatically so.




The blades rotate until they are inline with the shaft axis, how is this
not feathering?

take a look at the blades. they rotate and thus *reduce* drag, but they
certainly don't "feather".




I have, the blades rotate to line up with the axis of the shaft, how is
that *not* feathering?

of course, or very nearly so. That is what the word means. At least to the
professionals. rubber ducky sailors are a different breed, of course.

Subject: What are the pros and cons of a folding prop?
From: otnmbrd
Date: 8/31/2004 10:20 PM Eastern Daylight Time
Message-id: . net

So,Doodles, what you are saying, is that unless the blades are totally
flat, the term "feathering" can not be used?

otn

JAXAshby wrote:
the blades are curved, and rather dramatically so.




The blades rotate until they are inline with the shaft axis, how is this
not feathering?

take a look at the blades. they rotate and thus *reduce* drag, but they
certainly don't "feather".




I have, the blades rotate to line up with the axis of the shaft, how is
that *not* feathering?