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

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

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

(JAXAshby) wrote:

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

If you sail instead of sitting in the marina your boat will have a
clean bottom.

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.

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

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

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

On Sat, 28 Aug 2004 12:48:25 -0400, Glenn Ashmore
wrote:

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.

For what it's worth:

Buddy of mine with a steel Wallstrom-designed (partner to Brewer) 1979
ketch popped for a three-bladed AutoProp, a feathering design. He had
to haul out for many reasons: 1) to confirm the exact geometry of his
hull around the shaft; 2) to cut back his rudder at that point for the
install; and 3) to get the prop itself on. 1) was because it's
essentially a custom casting, and NOT cheap (about $3,500 Cdn.).

After three seasons now, he's happy as a clam with his decision and
outlay. He says the following:

Advantages:

Bigger prop, better bite and power curve. He's got a 35 HP Volvo
(probably 15-25 HP too small for a 28,000 lb. boat), but according to
him, the power he transmits to the prop is greatly increased. His top
speed without redlining has gone from 6.5 to 8.2 knots, or
approximately hull speed.

He says he gains 1/2 knot due to the self-feathering action, a
significant gain in typical light Lake Ontario air for this
essentially blue-water cruiser.

He backs down (after a quick rev to feather out the blades) far more
effectively now. He stops far more rapidly.

His docking is far more controlled. He can move his heavy, trad.
keeled boat like a minivan now. It's quite interesting to see.

Disadvantages:

The cones in his transmission have been wearing far more quickly and
have required replacement. He can handle this himself as a repair, so
it's more an annoyance than a tragedy, and spares from Volvo are
pricey.

He figures that shifting the gears with a bigger, heavier prop is
causing wear and tear beyond the engine spec. You can hear the "clunk"
of his shifting outside the boat, actually. He is consulting with a
marine engineer to determine a better course of action, but he is
leaning towards a shock-absorbing coupler and a thrust bearing
designed to isolate the engine transmission more effectively from the
sheer inertia of this otherwise fine prop.

Overall, he is so happy with the performance, however, both under sail
and power, that he would consider getting a new diesel to make full
use of the prop, rather than sticking with the small but still viable
diesel that perhaps doesn't have the beef at the back end to cope with
God's Own Feathering Prop G.

Hope this little tale helps.

R.

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

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

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.

For what it's worth:

Buddy of mine with a steel Wallstrom-designed (partner to Brewer) 1979
ketch popped for a three-bladed AutoProp, a feathering design. He had
to haul out for many reasons: 1) to confirm the exact geometry of his
hull around the shaft; 2) to cut back his rudder at that point for the
install; and 3) to get the prop itself on. 1) was because it's
essentially a custom casting, and NOT cheap (about $3,500 Cdn.).

After three seasons now, he's happy as a clam with his decision and
outlay. He says the following:

Advantages:

Bigger prop, better bite and power curve. He's got a 35 HP Volvo
(probably 15-25 HP too small for a 28,000 lb. boat), but according to
him, the power he transmits to the prop is greatly increased. His top
speed without redlining has gone from 6.5 to 8.2 knots, or
approximately hull speed.

He says he gains 1/2 knot due to the self-feathering action, a
significant gain in typical light Lake Ontario air for this
essentially blue-water cruiser.

He backs down (after a quick rev to feather out the blades) far more
effectively now. He stops far more rapidly.

His docking is far more controlled. He can move his heavy, trad.
keeled boat like a minivan now. It's quite interesting to see.

Disadvantages:

The cones in his transmission have been wearing far more quickly and
have required replacement. He can handle this himself as a repair, so
it's more an annoyance than a tragedy, and spares from Volvo are
pricey.

He figures that shifting the gears with a bigger, heavier prop is
causing wear and tear beyond the engine spec. You can hear the "clunk"
of his shifting outside the boat, actually. He is consulting with a
marine engineer to determine a better course of action, but he is
leaning towards a shock-absorbing coupler and a thrust bearing
designed to isolate the engine transmission more effectively from the
sheer inertia of this otherwise fine prop.

Overall, he is so happy with the performance, however, both under sail
and power, that he would consider getting a new diesel to make full
use of the prop, rather than sticking with the small but still viable
diesel that perhaps doesn't have the beef at the back end to cope with
God's Own Feathering Prop G.

Hope this little tale helps.

R.