JAXAshby wrote:
glenn, just where is it you found you "facts" that "a medium displacement boat"
has 2,866.66666666 pounds of drag?

From the VPP diagrams and backup data on my boat, the VPP for a
Beneteau First 47, C.A. Marchaj's "Sail Performance" and working
backwards from Dave Gerr's figures. The VPPs were run with standard and
Gori folding 3 bladed props and showed from 12 to 15% increased speeds
with the folding props up to about 80% of the first reef point.

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.

--
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

(JAXAshby) wrote:

Rosalie, your prop was also turning while you were running the engine. that
alone is one hell of a drag.

That's what I was saying. When the engine is running the prop is
turning. When we shut the engine down and feather the prop the prop
doesn't spin the shaft anymore. That's why we got it - so that the
shaft wouldn't spin under sail.

I don't know if the prop spinning under sail has more drag than one (a
three blade one) that is stationary but not feathered, but the only
way we could keep it from turning while under sail would be to put
vise grips on the shaft.

"Paul L" wrote:

You will definitely will see a decent speed improvement under sail with a
folding prop. Depending on the prop you buy, you should see better
power/control in reverse too. They are very reliable now, so I don't think
that is a down side. The biggest downside is their cost. I have a Max prop
and think it great.

Paul
www.jcruiser.org
"MLapla4120" wrote in message
...
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.


We have a feathering prop (vs a folding prop) and we do get an
increase of about 1/2 knot under sail, and it also backs better under
power. I haven't tried to quantify the backing under power - it is
just what we feel.

Disadvantages are - you lose a bit of power forward because the blades
are flat and the prop takes a bit more maintenance than a fixed prop.

[We were sailing but had the engine on in neutral so the prop was not
feathered - we were running the refrigeration- and when we had
finished that, we turned off the engine and feathered the prop, and
our speed increased 1/2 knot - same wind and current. Now I know this
is not a completely scientific test, but it is significant to us.
There are also people in our group who did tests with a fixed prop
over a measured course, and then did the same tests with a folding
prop over the same course and found a similar result.]




grandma Rosalie








grandma Rosalie

bite me.

"JAXAshby" wrote in message
...
Its real easy to test, as I can get my folding 3 blade to stay open. I
can
see the boat speed, then have it fold and measure the speed. It is
significant. If the MIT tests say otherwise then they are not testing
reality - wanna guess what errors they made in the test or you in the
interpretation??.

sure, paul lever knows more testing props than MIT. good on ya, paul.


Paul
www.jcruiser.org
"JAXAshby" wrote in message
...
You will definitely will see a decent speed improvement under sail with
a
folding prop

no, you won't. folding props only hve value for racing boats, where 2
seconds
a mile means the difference between 2nd place and 6th.

According to MIT tests, a folding prop means a savings of a mere 170
pounds
drag at 5 knots (or 40 pounds drag at 2-1/2 knots, or 10 pounds drag at
1-1/4
knots) over a --------- three ------------ blade prop. ***Much***
less
with
compared to a two-blade, and even less compared to a two-blade rotated
verticle
behind the keel.

Wanna guess just how much powered is required to pull 170# at 5 knots?

There aren't too many other things you can do to gain that much performance
that easily.

Paul
"Glenn Ashmore" wrote in message
news:OI2Yc.31945$A91.27814@okepread02...


JAXAshby wrote:
glenn, just where is it you found you "facts" that "a medium displacement
boat"
has 2,866.66666666 pounds of drag?

From the VPP diagrams and backup data on my boat, the VPP for a Beneteau
First 47, C.A. Marchaj's "Sail Performance" and working backwards from
Dave Gerr's figures. The VPPs were run with standard and Gori folding 3
bladed props and showed from 12 to 15% increased speeds with the folding
props up to about 80% of the first reef point.

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.

--
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

Uh huh, and the point would be?
"JAXAshby" wrote in message
...
Rosalie, your prop was also turning while you were running the engine.
that
alone is one hell of a drag.

"Paul L" wrote:

You will definitely will see a decent speed improvement under sail with
a
folding prop. Depending on the prop you buy, you should see better
power/control in reverse too. They are very reliable now, so I don't
think
that is a down side. The biggest downside is their cost. I have a Max
prop
and think it great.

Paul
www.jcruiser.org
"MLapla4120" wrote in message
...
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.


We have a feathering prop (vs a folding prop) and we do get an
increase of about 1/2 knot under sail, and it also backs better under
power. I haven't tried to quantify the backing under power - it is
just what we feel.

Disadvantages are - you lose a bit of power forward because the blades
are flat and the prop takes a bit more maintenance than a fixed prop.

[We were sailing but had the engine on in neutral so the prop was not
feathered - we were running the refrigeration- and when we had
finished that, we turned off the engine and feathered the prop, and
our speed increased 1/2 knot - same wind and current. Now I know this
is not a completely scientific test, but it is significant to us.
There are also people in our group who did tests with a fixed prop
over a measured course, and then did the same tests with a folding
prop over the same course and found a similar result.]




grandma Rosalie

now, THAT is an informed response.

From: "Paul L"
Date: 8/28/2004 2:01 PM Eastern Daylight Time
Message-id: nM3Yc.321$6q.104@trnddc06

bite me.

"JAXAshby" wrote in message
...
Its real easy to test, as I can get my folding 3 blade to stay open. I
can
see the boat speed, then have it fold and measure the speed. It is
significant. If the MIT tests say otherwise then they are not testing
reality - wanna guess what errors they made in the test or you in the
interpretation??.

sure, paul lever knows more testing props than MIT. good on ya, paul.


Paul
www.jcruiser.org
"JAXAshby" wrote in message
...
You will definitely will see a decent speed improvement under sail with
a
folding prop

no, you won't. folding props only hve value for racing boats, where 2
seconds
a mile means the difference between 2nd place and 6th.

According to MIT tests, a folding prop means a savings of a mere 170
pounds
drag at 5 knots (or 40 pounds drag at 2-1/2 knots, or 10 pounds drag at
1-1/4
knots) over a --------- three ------------ blade prop. ***Much***
less
with
compared to a two-blade, and even less compared to a two-blade rotated
verticle
behind the keel.

Wanna guess just how much powered is required to pull 170# at 5 knots?

Glenn, how does it feel to have a fish hook in your mouth?

the marketing people done did snag you.

170# at 5 knots is 85# at 2.5 knots is 42# a 1.25 knots. For a fixed
***three*** blade prop.

In other words, zip.

In fact, a two blade at 5 knots was IIRC about 75# and a two blade behind the
keel wwas about 45#.

In other words, "You how the f*&*% much to gain 0.05 knots speed??"

And, that damned feathering three blade cost you HOW much in forward speed
because the blades are flat?

Folding props are for race boat boats, and boat owners who like to brag how
much *they* spent on their boat. Sorta like the suburban home owner bragging
about spending $400/week to have his LARGE swimming pool cleaned.

btw, glenn, Dave Gerr rehashes other people's writings without all that much
verification.

glenn, just where is it you found you "facts" that "a medium displacement
boat"
has 2,866.66666666 pounds of drag?

From the VPP diagrams and backup data on my boat, the VPP for a
Beneteau First 47, C.A. Marchaj's "Sail Performance" and working
backwards from Dave Gerr's figures. The VPPs were run with standard and
Gori folding 3 bladed props and showed from 12 to 15% increased speeds
with the folding props up to about 80% of the first reef point.

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.

--
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

There aren't too many other things you can do to gain that much performance
that easily.

sure there are. you can clean the bottom of your boat. you can thoroughly
fair the hull before you bottom paint. you can take 500# of useless junk out
of your boat. you can trim the sails. you can buy better sails. you can take
down your dodger and/or bimini and/or 3 of your 8 solar panels. you can use a
hank on jib instead of a roller furled jib. you can use a vinyl bottom paint.
you can do polars on your boat to sail it smarter. you can move your anchor
and 275 foot of chain to the center of the boat. you can sail more so you need
300# less fuel onboard. ----------------------- you can install a two blade
prop ------------------------- which i damned cheap and damned effective. you
can line up your prop with the keel.

To name just a few.



Paul
"Glenn Ashmore" wrote in message
news:OI2Yc.31945$A91.27814@okepread02...


JAXAshby wrote:
glenn, just where is it you found you "facts" that "a medium displacement
boat"
has 2,866.66666666 pounds of drag?

From the VPP diagrams and backup data on my boat, the VPP for a Beneteau
First 47, C.A. Marchaj's "Sail Performance" and working backwards from
Dave Gerr's figures. The VPPs were run with standard and Gori folding 3
bladed props and showed from 12 to 15% increased speeds with the folding
props up to about 80% of the first reef point.

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.

--
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

I don't know if the prop spinning under sail has more drag than one (a
three blade one) that is stationary but not feathered,

It does, but quite a bit.

uhhhhhhhh, mmc? which word didn't you understand?

From: "MMC"
Date: 8/28/2004 3:34 PM Eastern Daylight Time
Message-id:

Uh huh, and the point would be?
"JAXAshby" wrote in message
...
Rosalie, your prop was also turning while you were running the engine.
that
alone is one hell of a drag.

"Paul L" wrote:

You will definitely will see a decent speed improvement under sail with
a
folding prop. Depending on the prop you buy, you should see better
power/control in reverse too. They are very reliable now, so I don't
think
that is a down side. The biggest downside is their cost. I have a Max
prop
and think it great.

Paul
www.jcruiser.org
"MLapla4120" wrote in message
...
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.


We have a feathering prop (vs a folding prop) and we do get an
increase of about 1/2 knot under sail, and it also backs better under
power. I haven't tried to quantify the backing under power - it is
just what we feel.

Disadvantages are - you lose a bit of power forward because the blades
are flat and the prop takes a bit more maintenance than a fixed prop.

[We were sailing but had the engine on in neutral so the prop was not
feathered - we were running the refrigeration- and when we had
finished that, we turned off the engine and feathered the prop, and
our speed increased 1/2 knot - same wind and current. Now I know this
is not a completely scientific test, but it is significant to us.
There are also people in our group who did tests with a fixed prop
over a measured course, and then did the same tests with a folding
prop over the same course and found a similar result.]




grandma Rosalie