wrote:
Joe wrote:
wrote:
A question sometimes asked is that if you have a large fan at the
stern on a
sailboat blowing forward into the sails would that propel the boat
forward? The usual answer given is no because the fan blowing air
forward would produce momentum propelling the boat backwards. This
would swamp the effect of an effective wind acting on the sails.
But suppose instead you had the fan in front blowing rearward into the
sails?
In this case the momentum would propel the boat forward. Furthermore by
using the method of tacking into the wind, the wind blowing into the
sails could produce a force with a forward component as well. Then the
acceleration forward should be higher than that produced by the
momentum flow of the fan alone. The speed could also be higher than the
speed of the air created by the fan since tacking into the wind can
give you a higher speed than the wind speed.
Would this work?



Yes it works!
I'm in the process of mounting this fan on my bow pulpit.
Making the swivel braket is the hardest part, air flow entry angle is
important.
I hope to gain 13kts:
http://www.superiorairparts.com/Wall...er1024x768.jpg

Joe



Have you performed any tests that lead you to believe the speed can be
greater than by putting the fan at the stern?
That is, will the fan in the front blowing over the sails increase
speed more than when it is at the rear and not blowing over the sails?


Bob Clark

Here's another way to look at the scenario. Suppose you had your giant
fan on a raft with no sail or keel. This raft is connected to the
sailboat by a rope. Suppose this rope initially is slack. You turn on
the fan directed towards the sailboat. The wind produced by the fan
allows the sailboat to move forwards by tacking into the wind. The raft
and fan also move forwards separately due to the momentum thrust of the
fan. The instant the rope is about to become taut you turn off the fan.
When the rope tightens, the sailboat will get a higher speed because of
the forward momentum of the raft. The raft will also be pulled backward
but it won't affect the forward speed of the boat as long as it does
not contact the boat. You make the rope long enough so this doesn't
happen. Once the rope is slack again. You turn on the fan again. The
process repeats.
You see the result will be that the sailboat will wind up having a
speed due to *both* the wind produced by the fan acting on the sails
and from the momentum thrust produced by the fan.


Bob Clark

wrote in news:1153667730.918826.254080
@p79g2000cwp.googlegroups.com:

Would this work?


No.

Airboats with just the fan go 70 mph, even over wet grass. I haven't seen
any sails on any of them to increase speed.

Let's think....If we put an airboat engine/fan on the bow blowing through
all that wind resistance of rigging and sails and tackle and measure the
speed.....then, clean the deck of all sailing paraphenalia and let the
airboat fan power the boat with no sailing equipment, its drag, its weight,
its moment pulling the boat over...

Which do YOU think would be faster?

I'm picking Door Number Two!

Larry wrote:
wrote in news:1153667730.918826.254080
@p79g2000cwp.googlegroups.com:

Would this work?


No.

Airboats with just the fan go 70 mph, even over wet grass. I haven't seen
any sails on any of them to increase speed.

Let's think....If we put an airboat engine/fan on the bow blowing through
all that wind resistance of rigging and sails and tackle and measure the
speed.....then, clean the deck of all sailing paraphenalia and let the
airboat fan power the boat with no sailing equipment, its drag, its weight,
its moment pulling the boat over...

Which do YOU think would be faster?

I'm picking Door Number Two!

Thanks for the response. I didn't know airboats could go that fast.
The key fact that makes me think it could go faster is that with a
motor driven boat there is created apparent wind from its motion even
in still air. The wind speed of this apparent wind is the speed of the
boat of course (in still air.) But it is known that sailboats can
*exceed* the wind speed:

The physics of sailing.
"How can boats sail faster than the wind? Lots of boats
can---especially the eighteen footer skiffs on Sydney Harbour. Ask a
sailor how, and he'll say "These boats are so fast that they make their
own wind", which is actually true. Ask a physicist, and she'll say that
it's just a question of vectors and relative velocities."
....
"The faster that the boat goes, the greater the relative wind, the more
force there is on the sails, so the greater the force dragging the boat
forwards. So the boat accelerates until the drag from the water
balances the forward component of the force from the sails."
....
"Why are eighteen footers always sailing upwind?
In a fast boat, there's no point going straight downwind: you can never
go faster than the wind. So you travel at an angle. But if your boat is
fast enough, then the relative wind always seems to be coming mainly
from ahead of you, as these arrows show. So the eighteen footers never
set ordinary spinnakers: they have asymmetrical sails that they can set
even when they are travelling at small angles to the apparent wind."
http://www.phys.unsw.edu.au/~jw/sailing.html

Furthermore it has been proven that propeller driven boats that have
sails can achieve higher speeds with the sails than from the propeller
alone:

Motorsailing - Some Thoughts.
"Based on my experience the motorsailer is the most practical and
comfortable vessel for serious ocean passagemaking. However these days
power-only long range cruising yachts seem to be the rage. We sell
about 8 power boats for each motorsailer we build. I personally can not
understand the long range powerboat skipper generating a beautiful 7 to
9 knot wind, at some cost, and than just throwing it away - while
worrying about fuel?"
....
"Plus the sailing rig increases the speed of the vessel so less fuel
capacity is needed. This weight savings coupled with the additional
propulsion power available results in faster passages and excellent
fuel economy.
"How can this be? Well most power-only trawler yachts cruise at around
6 to 8 knots per hour depending on power, weight, hull shape and water
line length. All these vessels are creating, at some expense, a wind
equal to their speed. This wind, a vital and reliable source of energy,
combines with and adds to the true wind to create an apparent wind
across the boat which is just thrown away. The motorsailer, on the
other hand, uses its rig to regain this energy resulting in increased
boat speed, up to 25% above a stabilized powerboat, without increasing
fuel use."
http://www.seahorseyachts.com/seahor...emarine_3.html

So a fan at the stern blowing *rearward* with the sails forward, so
the fan does not blow over the sail, could likewise increase speed,
just as with the motorsailers.
What I'm asking is if in fact you did put that fan in front of the
sails so the air did blow over them, would this increase speeds even
better than the fan at the stern case.


Bob Clark

This brings back memories of long and
heated discussions about whether a
windmill on a boat could propel the boat
directly into the wind.

Assume either electric power generated
by the windmill or direct mechanical
connection to the prop.

Have at it!

Chuck


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chuck wrote in news:1153691380_100797
@sp6iad.superfeed.net:

This brings back memories of long and
heated discussions about whether a
windmill on a boat could propel the boat
directly into the wind.

Assume either electric power generated
by the windmill or direct mechanical
connection to the prop.

Have at it!



Jacques Cousteau did it. The windmill was vertical so it ran the
propulsion with apparent wind from any direction. There were 4 of them as
I remember on a good-sized ship.

http://openweb.tvnews.vanderbilt.edu...21-CBS-19.html

IT worked but had mechanical problems.

Actually, someone from Australia did just that. Well engineered, and
successful. Would go about the same speed in all directions.
I wish I could remember where I read about it but it must have been 20 years
ago.

"chuck" wrote in message
...
This brings back memories of long and heated discussions about whether a
windmill on a boat could propel the boat directly into the wind.

Assume either electric power generated by the windmill or direct
mechanical connection to the prop.

Have at it!

Chuck


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News==----
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Newsgroups
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wrote in message
oups.com...
A question sometimes asked is that if you have a large fan at the
stern on a
sailboat blowing forward into the sails would that propel the boat
forward? The usual answer given is no because the fan blowing air
forward would produce momentum propelling the boat backwards. This
would swamp the effect of an effective wind acting on the sails.
But suppose instead you had the fan in front blowing rearward into the
sails?
In this case the momentum would propel the boat forward. Furthermore by
using the method of tacking into the wind, the wind blowing into the
sails could produce a force with a forward component as well. Then the
acceleration forward should be higher than that produced by the
momentum flow of the fan alone. The speed could also be higher than the
speed of the air created by the fan since tacking into the wind can
give you a higher speed than the wind speed.
Would this work?


Bob


Okay, here's what you do:

Install a high-efficiency air compressor belowdecks. Connect this to a
modified luff foil into which precisely sized holes have been drilled at an
angle which allows for maximum efficiency of turbulated airflow across both
the back and front of the sail, with the speed at the back being greater
than that at the front (precise differential you will have to calculate
yourself for your specific sail). Do this for all sails. Report back. :-)

Karin Conover-Lewis
Rawson 30 ketch "Escapade"
Marinette WI

Questions like this remind me of the old Popeye cartoons, where Popeye
thows an old bathtub into the sea, and then, whith a shower head on the
end of a pipe, crams it into the drain. viola! Instant water jet! town
pressure on tub forces water through shower head, and instant
propulsion.

Another Idea that looks good on paper.......



wrote:
A question sometimes asked is that if you have a large fan at the
stern on a
sailboat blowing forward into the sails would that propel the boat
forward? The usual answer given is no because the fan blowing air
forward would produce momentum propelling the boat backwards. This
would swamp the effect of an effective wind acting on the sails.
But suppose instead you had the fan in front blowing rearward into the
sails?
In this case the momentum would propel the boat forward. Furthermore by
using the method of tacking into the wind, the wind blowing into the
sails could produce a force with a forward component as well. Then the
acceleration forward should be higher than that produced by the
momentum flow of the fan alone. The speed could also be higher than the
speed of the air created by the fan since tacking into the wind can
give you a higher speed than the wind speed.
Would this work?


Bob

like the cartoon axiom which states, "cartoon characters may be unaffected
by gravity and may be supported by thin air, but only so long as they are
unaware of their current, unsupported status."
Scout

wrote in message
ups.com...

Questions like this remind me of the old Popeye cartoons, where Popeye
thows an old bathtub into the sea, and then, whith a shower head on the
end of a pipe, crams it into the drain. viola! Instant water jet! town
pressure on tub forces water through shower head, and instant
propulsion.

Another Idea that looks good on paper.......



wrote:
A question sometimes asked is that if you have a large fan at the
stern on a
sailboat blowing forward into the sails would that propel the boat
forward? The usual answer given is no because the fan blowing air
forward would produce momentum propelling the boat backwards. This
would swamp the effect of an effective wind acting on the sails.
But suppose instead you had the fan in front blowing rearward into the
sails?
In this case the momentum would propel the boat forward. Furthermore by
using the method of tacking into the wind, the wind blowing into the
sails could produce a force with a forward component as well. Then the
acceleration forward should be higher than that produced by the
momentum flow of the fan alone. The speed could also be higher than the
speed of the air created by the fan since tacking into the wind can
give you a higher speed than the wind speed.
Would this work?


Bob

That reminds me of: If from the top of your mast you drop a hand tool when
your boat is sailing a 5 - 6 knots where will it land? The answer is right
on you boat. I wonder why? Could the same phenomena applies to a fan
attached on a boat blowing on its sail to provide propulsion?

"Scout" wrote in message
...
like the cartoon axiom which states, "cartoon characters may be unaffected
by gravity and may be supported by thin air, but only so long as they are
unaware of their current, unsupported status."
Scout

wrote in message
ups.com...

Questions like this remind me of the old Popeye cartoons, where Popeye
thows an old bathtub into the sea, and then, whith a shower head on the
end of a pipe, crams it into the drain. viola! Instant water jet! town
pressure on tub forces water through shower head, and instant
propulsion.

Another Idea that looks good on paper.......



wrote:
A question sometimes asked is that if you have a large fan at the
stern on a
sailboat blowing forward into the sails would that propel the boat
forward? The usual answer given is no because the fan blowing air
forward would produce momentum propelling the boat backwards. This
would swamp the effect of an effective wind acting on the sails.
But suppose instead you had the fan in front blowing rearward into the
sails?
In this case the momentum would propel the boat forward. Furthermore by
using the method of tacking into the wind, the wind blowing into the
sails could produce a force with a forward component as well. Then the
acceleration forward should be higher than that produced by the
momentum flow of the fan alone. The speed could also be higher than the
speed of the air created by the fan since tacking into the wind can
give you a higher speed than the wind speed.
Would this work?


Bob