(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 30 Aug 2004 03:34:57 GMT, (JAXAshby) wrote:

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

From www.autoprop.com

"In forward the propellor rotates to the correct pitch automatically.
This results in increased propulsion efficiency whcih reduces fuel
consumption, and extends cruising range.

"While under sail the propellor feathers itself to reduce drag by 85%
compared to conventional 3-blade propellors.

"The Autoprop also self pitches in reverse to give you the same thrust
in reverse as you would get in forward. This greatly improves stopping
power, backing down, and overall maneuverability."

Note the use of the word "feather" as in "feathers itself", a concept
with which I believe you would be familiar, JAX, particularly on
those lonely Saturday nights.


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

That "clown" has seen more salt water than Mr. Morton during a flash
flood, JAX, including the first private yacht transit of Hudson's Bay
since...well, Hudson, so let's just say he doesn't quite have the
credibility gap you exhibit with most of your bilious, ill-informed,
poorly argued and borderline dyslexic posts.

Now, punk, go measure a footwell or something. Sailors are speaking
here.

Really, could the barrel get any smaller or the fish and the cannon
any bigger?

R.

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?

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

otn

let me help improve, over the knee, with your understanding of English words.

v. feath·ered, feath·er·ing, feath·ers

v. tr.
To turn (an oar blade) almost horizontal as it is carried back after each
stroke.

To alter the pitch of (a propeller) so that the chords of the blades are
parallel with the line of flight.

In article ,
(MLapla4120) wrote:

I'm going to re-power soon and am also going to get new shaft and prop.
It seems that in my boat class (Westsail 32), some people are going
to folding props to help speed under sail.
I'm for increased speed, but also want reliability. My current bronze
propeller is pitted and old. Every time I turn around and look at it, it
is full of sea growth. That makes me think I'm getting poor performance.
So, I'm for an improvement, but I am unsure of what kind.
Any opinions from boaters that have encountered this situation would be
appreciated.

Thanks,
Mark , "Belle" Westsail 32

ANY modern prop will improve your performance under power, forward and
reverse. Technology has improved in 30 years.

A feathering prop can drastically improve sailing enjoyment if you don't
bother to park your prop behind the keel. Your Westsail may not get the
improvements we get as we're lighter and cleaner, but we pick up .5 to
..8 knots when I remember to stop the prop, which has us sailing more
than we used to.

Windward performance improved, allowing us to get a bit closer to the
wind.

We also get more comfortable sailing past hull speed, but the "wetsnail"
doesn't have a hullform that allows much of that.

--
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/