What are the pros and cons of a folding prop?
 

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

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.

Thanks,
Mark , "Belle" Westsail 32

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?

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?

Assuming you're talking about a sailboat, then I'm currently taking a
look at www.kiwiprops.co.nz which look neat, and the testimonials
read well. But I've no personal experience. I'd like to hear from
anyone who has

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?

As usual, Jax has taken some good data and come up with a completely
erroneous conclusion. The drag from the prop increases as the square of
the speed. Using the MIT figures, at 8 knots you are looking at
something over 430 pounds of drag. For a medium displacement boat that
can add up to 15% or more in improved performance. For a 40' LWL
cruiser that means an extra 20 to 25 miles a day.

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?






--
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

"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

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

btw, "a medium displacement boat" that does 8 knots continuous is rare indeed.

btw-2: that 15% that is so often bandied about comes from a marketing
department at a folding prop company.

btw-3: ------ folding -------- three blade props are rare indeed.

btw-4: the subject of this thread is folding, not feathering (a hugely more
expensive breed of cat)

btw-5, the 170# figures from MIT were for --------- three --------- bladed
props. Two bladed props have much less drag, and two bladed props aligned
behind the keel have even less.

btw-6, when the winds are sufficient to drive ""a medium displacement boat" at
8 knots, you have more than enough wind to drive the boat at 8 knots with a
bucket dragging behind just by putting up anothe 20 square feet of sail.

btw-7: most folding/feathering props are promoted by their marketers as an
improvement in **LITE** airs, not heavy.


As usual, Jax has taken some good data and come up with a completely
erroneous conclusion. The drag from the prop increases as the square of
the speed. Using the MIT figures, at 8 knots you are looking at
something over 430 pounds of drag. For a medium displacement boat that
can add up to 15% or more in improved performance. For a 40' LWL
cruiser that means an extra 20 to 25 miles a day.

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?






--
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

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