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?

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?

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?

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.

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

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

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