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

Yes, you won't even need the sail!
http://www.answers.com/topic/air-boat-jpg
Scout

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

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?


Of course it will. Haven't you ever watched a Popeye
cartoon?

SV

Would this work?



No, and we promptly removed our GE fan from the swim platform at the
start of the season. The fan cost more than Scotty's boat.


RB
35s5
NY

Wind blowing on bare poles will make the boat go.

The apparent wind created by a boat drifting withe the current (in still air
relative to the ground) will make it go faster than the current.

Yes, the fan blown into the sail at the correct locations will increase boat
speed. Blowing it from the rear and using ballistic theory will not yield
the true answer. Blowing the fan over the sails and correctly applying
Bernoulli's Laws shows the sailboat will indeed move forward. Under the
right conditions the sailboat will move faster than the windspeed of the
fan.

I am an intellectual (Mensa member in good standing), look great in Speedos
and wonder if LP is available. Kates keeps on standing me up - without
Viagra!

Jax

Jax wrote:
snip
I am an intellectual (Mensa member in good standing), look great in Speedos
snip..

Jax



Sez who? We've been subjected to the pictures unfortunately.

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



Bob

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!

Somebody said that you died of aids...



Jax typed:
Wind blowing on bare poles will make the boat go.

The apparent wind created by a boat drifting withe the current (in
still air
relative to the ground) will make it go faster than the current.

Yes, the fan blown into the sail at the correct locations will
increase boat
speed. Blowing it from the rear and using ballistic theory will not
yield
the true answer. Blowing the fan over the sails and correctly
applying
Bernoulli's Laws shows the sailboat will indeed move forward. Under
the
right conditions the sailboat will move faster than the windspeed of
the
fan.

I am an intellectual (Mensa member in good standing), look great in
Speedos
and wonder if LP is available. Kates keeps on standing me up -
without
Viagra!

Jax

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