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

about 2-1/2 hp. that's a LOT, isn't it.

There is another J36 at our marina, which has a fixed prop. It is
astonishingly slower than our boat. I know the sails aren't identical,
but we have caught them going to windward when we didn't even have a
jib hoisted.

Their bottom is cleaner or as clean.On Sat, 28 Aug 2004 05:02:39 GMT,
"Paul L" wrote:

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??.

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?




Rodney Myrvaagnes NYC


We have achieved faith-based science,
faith-based economics, faith-based law
enforcement, and faith-based missile
defense.
What's next? Faith-based air traffic control?

Subject: What are the pros and cons of a folding prop?
From: Rosalie B.

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


Question. Your engine was running but you were in neutral gear. Why wasn't the
prop feathered? i.e., does the prop "unfeather" when the engine starts or when
you put it in gear? What causes the prop to feather?
This is an area I'm not familiar with, though I frequently use VP/CP props.

Shen

putting a folding prop on Westsail is like putting Nikes on an obese man.

The person that inquired has a Westsail. This is not a racing boat.
He wants to sail faster WITH the dodger and bimini, and with the
roller furled jib and with the solar panels and the fuel etc. He
isn't racing.

Just because these are all things that can make a boat go faster
doesn't mean that they are viable options for a cruising sailboat nor
that the folding prop isn't also an option that he can use
effectively.


grandma Rosalie

The other way of looking at it is that the Westsail needs all the help it
can get ;-))
Bob Larder

JAXAshby wrote:
putting a folding prop on Westsail is like putting Nikes on an obese
man.

The person that inquired has a Westsail. This is not a racing boat.
He wants to sail faster WITH the dodger and bimini, and with the

Back in my racing days I used a Martec II folding prop. It I remember right
(Martec recommended) it was a 14x12 and replaced a 16x10 2 bladed and worked
ok. It was on a Yanmar 2GM20F. Less power in forward and significantly
less power in reverse. You need to be much more aggressive in reverse when
docking. Lots more walk to port also. Still had to line up the shaft (I
used the keyway since the two were inline) to get it to fold in light air
since the weight of the prop would cause it to open. I have even heard of
folks jumping overboard and putting a rubber band around them to keep it
closed. If it got fouled with growth so it would not open all the way it
would let you know by vibrating when trying to go forward. This is just
some of the things you need to put up with when you race.

I believe it did fold when going from forward to reverse. You could hear it
go "clunk."

With my current cruising boat I would look at feathering props if I were to
upgrade. I need a good reverse and these provide it.

I guess the question is did it help? I would guess so. Could I tell? No
not really.

I agree with JAX. There is quite a bit of stuff you can do to the bottom of
the boat for speed. But bolting on a folding prop is definitely easy. The
other speed improvements require hard work.


"Rosalie B." wrote in message
...
(Shen44) wrote:

Subject: What are the pros and cons of a folding prop?
From: Rosalie B.

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.]

Question. Your engine was running but you were in neutral gear. Why wasn't
the
prop feathered? i.e., does the prop "unfeather" when the engine starts or
when
you put it in gear? What causes the prop to feather?
This is an area I'm not familiar with, though I frequently use VP/CP
props.


I don't know what a VP/CP prop is.

When our engine is running the shaft is spinning because we have a
Borg-Warner transmission. Our shaft spins whenever the engine is on
regardless whether it is neutral or not. The prop feathers when the
engine is turned off and the shaft stops spinning. The stopping of
the shaft spinning feathers the prop if I understand it correctly.
You really wouldn't want the prop feathered if the engine was on - if
it feathered when you went through neutral when docking or something
it would be very awkward.



grandma Rosalie

"Rick" wrote:

Back in my racing days I used a Martec II folding prop. It I remember right

I have been told that a folding prop and a feathering prop are
different. I haven't seen a folding prop, so I don't know what the
difference is.

(Martec recommended) it was a 14x12 and replaced a 16x10 2 bladed and worked
ok. It was on a Yanmar 2GM20F. Less power in forward and significantly
less power in reverse. You need to be much more aggressive in reverse when
docking. Lots more walk to port also. Still had to line up the shaft (I
used the keyway since the two were inline) to get it to fold in light air
since the weight of the prop would cause it to open. I have even heard of
folks jumping overboard and putting a rubber band around them to keep it
closed. If it got fouled with growth so it would not open all the way it
would let you know by vibrating when trying to go forward. This is just
some of the things you need to put up with when you race.

Yes, I sometimes go over to check and see if the prop is moving freely
and to wipe or chip off growth.

We had a 3 blade prop to start with, and we put on a 3 blade
feathering prop that was as close to the diameter and pitch of the old
prop as possible.

I believe it did fold when going from forward to reverse. You could hear it
go "clunk."

This is transmission dependent to a certain extent. Our transmission
goes clunk when going from forward to reverse. I can't hear the prop
feather. The only way we know if it has not feathered is that we can
still hear the shaft rotating.

With my current cruising boat I would look at feathering props if I were to
upgrade. I need a good reverse and these provide it.

I guess the question is did it help? I would guess so. Could I tell? No
not really.

I agree with JAX. There is quite a bit of stuff you can do to the bottom of
the boat for speed. But bolting on a folding prop is definitely easy. The
other speed improvements require hard work.


"Rosalie B." wrote in message
.. .
(Shen44) wrote:

Subject: What are the pros and cons of a folding prop?
From: Rosalie B.

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.]

Question. Your engine was running but you were in neutral gear. Why wasn't
the
prop feathered? i.e., does the prop "unfeather" when the engine starts or
when
you put it in gear? What causes the prop to feather?
This is an area I'm not familiar with, though I frequently use VP/CP
props.


I don't know what a VP/CP prop is.

When our engine is running the shaft is spinning because we have a
Borg-Warner transmission. Our shaft spins whenever the engine is on
regardless whether it is neutral or not. The prop feathers when the
engine is turned off and the shaft stops spinning. The stopping of
the shaft spinning feathers the prop if I understand it correctly.
You really wouldn't want the prop feathered if the engine was on - if
it feathered when you went through neutral when docking or something
it would be very awkward.



grandma Rosalie


grandma Rosalie

Rosalie B. wrote:

I don't know what a VP/CP prop is.

variable pitch/constant pitch
the former you can feather, the latter you can't