How much horsepower?
Mr Norman Man Kei Ho
generated by a sail, say 6.5m in 20 knots wind? Just interested why the
windsurfer can go as fast as a fully powered pleasure craft.
--
Norman Ho
hongkong
Peter Somlo
I guess you wouldn't get a relatively large HP value because when a board
is PLANING its drag is much less than that of a `powered pleasure craft'.
Hope this helps.. Cheers.
--
Dr Peter I Somlo FIEEE | Motto1: "Every coin has 3 sides - at least"
Microwave Consultant | Motto2: "Beware of windsurfing - it's addictive"
tel/fax: 61-2-451-2478 | Internet: so...@kralizec.zeta.org.au
Richard R. Thomas
------------------------------------------------------------------------
Norman,
Sails are not engines. Sails can produce air pressure differentials
not horse power.
Sails can be considered to be wind kinetic energy collector/converters
when used as part of a moving system, ie. a sailboard system,
(sailboard/rig/sailor).
Sail size cannot be directly related to the "rate of work done" of a moving
sailboard system because of the numerous other variables involved.
E-mail me if you would like more info.
Regards.
--------------------------------------
Rick Thomas.
S.T.O.
Chemistry Dpt.
University of Tasmania.
Australia.
radi...@cc.memphis.edu
> On 4 Nov 1994, Mr Norman Man Kei Ho wrote:
>
>> Can anyone of you technical guys give me some hints about the horsepower
>> generated by a sail, say 6.5m in 20 knots wind? Just interested why the
>> windsurfer can go as fast as a fully powered pleasure craft.
> Sails are not engines. Sails can produce air pressure differentials
> not horse power.
True, power is force x distance over which the force worked / time required for
the force to cary the "object" over that distance
> Sails can be considered to be wind kinetic energy collector/converters
> when used as part of a moving system, ie. a sailboard system,
> (sailboard/rig/sailor).
> Rick Thomas.
Rick is right about that. Lets just try to give a simple first approximation.
The fluid mechanics manual that I have is from the undergrad days and
approximates the force as:
F=p x Q^2 / A
This doesn't look quite right to me since we're deviding by the area, but lets
go ahead with the analysis. p= the density of the fluid. Q is the flow rate of
the fluid (in this case the velocity of the air times the area of the sail).
A is the area of the sail. Try p=1.1614 kg/m^3 for air at 300 K.
Try the math and see if it works out.
Gotta run...
Robb
Peter Somlo
However, IMHO it is a valid question to ask: How powerful would an
engine have to be (thay weighed as much as the rig) to result in an
identical (planing) speed as I travel with the sail?
Cheers,
Volker Wedemeier
On 25 Nov 1994 radi...@cc.memphis.edu wrote:
> In article <Pine.SUN.3.90.941117...@tasman.cc.utas.edu.au>, "Richard R. Thomas" <che...@tasman.cc.utas.edu.au> writes:
> > On 4 Nov 1994, Mr Norman Man Kei Ho wrote:
> >
> >> Can anyone of you technical guys give me some hints about the horsepower
> >> generated by a sail, say 6.5m in 20 knots wind? Just interested why the
> >> windsurfer can go as fast as a fully powered pleasure craft.
>
> > Sails are not engines. Sails can produce air pressure differentials
> > not horse power.
>
> True, power is force x distance over which the force worked / time required
> for the force to cary the "object" over that distance
Yes, so sails of course _do_ create horse powers. That's what keeps us
moving.
> The fluid mechanics manual that I have is from the undergrad days and
> approximates the force as:
>
> F=p x Q^2 / A
>
> This doesn't look quite right to me since we're deviding by the area, but lets
> go ahead with the analysis. p= the density of the fluid. Q is the flow rate of
> the fluid (in this case the velocity of the air times the area of the sail).
> A is the area of the sail. Try p=1.1614 kg/m^3 for air at 300 K.
>
> Try the math and see if it works out.
>
> Gotta run...
> Robb
Well, I think this equation is a little bit too much out of the context!
But we could do a much more simple approach to at least get some sort of
rough estimate.
Considering, that on a windy day, you can put all your weight onto the
rigg, with the sail inclined 45 deg into the wind, one finds, that you
(can) have a lateral force of about 80kg * g = 800 N.
But what we need is not the lateral force, but the forward component of it.
I'd say it's not more than 200 N when you are at top speed, but probably
rather 100 N. Now let's say you go 40 km/h, which is about 11 m/s,
then you get a power-output of the sail of
P = 100 N * 11 m/s = 1100 Nm/s = 1100 Watts
So the power of a sail should be somewere around 1.1 kW but never much
more than 2.2 kW.
(In horsepowers: 1.1 kW = 1.5 hp and 2.2 kW = 3 hp)
I think those numbers sound quite reasonable, but I think the real
numbers are still somewhat less. Maybe 1 hp or something.
Volker
Richard Engelbrecht-Wiggans
Volker Wedemeier <wede@x4u2> writes:
>
>But we could do a much more simple approach to at least get some sort of
>rough estimate.
>
>Considering, that on a windy day, you can put all your weight onto the
>rigg, with the sail inclined 45 deg into the wind, one finds, that you
>(can) have a lateral force of about 80kg * g = 800 N.
>But what we need is not the lateral force, but the forward component of it.
>I'd say it's not more than 200 N when you are at top speed, but probably
>rather 100 N. Now let's say you go 40 km/h, which is about 11 m/s,
>then you get a power-output of the sail of
>
>
>So the power of a sail should be somewere around 1.1 kW but never much
>more than 2.2 kW.
>(In horsepowers: 1.1 kW = 1.5 hp and 2.2 kW = 3 hp)
>
>I think those numbers sound quite reasonable, but I think the real
>numbers are still somewhat less. Maybe 1 hp or something.
>
I doubt it is as little as 1 hp.
A human can put out something like 1 hp for a short while
(1 hp = 550 ft pounds/sec, and so I am putting out 1 hp
when I run up stairs at a rate of 3 (vertical) feet per
second, which I can do for a short while).
Some pretty smart people have put their minds to designing
fast human powered boats, but haven't been able to do much
better than an eight person rowing shell. Race speed for
a good eight is about 6 minutes for a 2000 meter course,
or about 12 miles per hour; that's WAY below the 40 mph
readily easily obtained on a sailboard. Even for short
distances, rowing shells can't go much faster.
Also, I have a sliding rigger setup for my course board,
and even though I can put out 1 hp for a short while--
and have decent rowing technique--I can't come close to
getting the board on a plane (at top rowing speed, the
board feels--and its wake looks--exactly like what it does
when slogging it out with a sail in very light air.)
My top speed rowing a sailboard is about 6 mph for short
bursts, while I can top 10 mph in a rowing shell; the
sailboard must get up on a plane to go fast, and I am
reasonably sure that doing so requires more than 1 hp.
So...I believe it takes a bit more than 1 hp to push
a sailboard 40 mph; the previous estimate of 1.5 to 3
hp seems reasonable to me.
Richard
MclAlex
(Richard Engelbrecht-Wiggans) writes:
This seems extraordinarily complicated!
Isn't it possible to put a rig in a windtunnel and measure the force in
footpounds?
Also...that three horsepower number can't be right...look at the
jetski/trashmobiles on a plane...how much power do those things need to
move?
Richard Engelbrecht-Wiggans
access to one. If someone does, fine. In the meantime, maybe
if we pool what information we DO have, we can come up with a
reasonable estimate.
In a previous post, I opined that 1 hp seems low. Now I'll suggest
that the horsepower of a PWV is much greater than that generated
by a sailboard rig. First, a typical PWC weighs a heck of a lot
more than a sailboard; I remember helping two other strong adults
trying to muscle one up a beach. I would guess that--togeather
with the operator--a PWC weighs three or four times as much as
does a sailboard. I am not sure how power scales up with weight,
but wouldn't be surprised if "4 times as heavy" means "4 times
as much power required to move it at the same speed."
Second: how many horsepower does a PWC actually produce? (As I
understand it, at least with automobiles, the stated hp of a
gasoline engine is MUCH higher than the actual hp that it typically
produces.)
Third: it takes some energy to produce all that noise. Heck, even
if a PWC consumed gasoline at a rate equivalent to 100 horsepower
of power, I would (almost) believe that 90 percent of it went into
making noise, leaving at most 10 hp for propulsion, which means
that 3 hp might well suffice to propel a correspondingly lighter
sailboard. ( :-) for those of you who think I'm am serious in
this last paragraph).
Richard.
Backwinded
(Richard Engelbrecht-Wiggans) writes:
I lost a 5$ bet to my brother in law. I said that my 1.2 hp Aqua Bug
outboard engine would not propell my AHD Eliminator over 5mph. I lost the
bet as the board went about 8mph Wide Open Throttle. I hand held the thing
and burned my hand and leg to boot!
I wonder how much hp it would take to make the board go 25mph?
Patrick Powers
I don't really know, but it seems to me that windsurfers are models of
efficiency and jetskis rather the reverse.
Albert Wilkes
In article <Pine.SGI.3.91.941126044740.13524B-100000@x4u2>
Volker Wedemeier <wede@x4u2> writes:
>>But we could do a much more simple approach to at least get some sort of
>>rough estimate.
>>
>>Considering, that on a windy day, you can put all your weight onto the
>>rigg, with the sail inclined 45 deg into the wind, one finds, that you
>>(can) have a lateral force of about 80kg * g = 800 N.
>>But what we need is not the lateral force, but the forward component of it.
>>I'd say it's not more than 200 N when you are at top speed, but probably
>>rather 100 N. Now let's say you go 40 km/h, which is about 11 m/s,
>>then you get a power-output of the sail of
>>
>
>>
>>So the power of a sail should be somewere around 1.1 kW but never much
>>more than 2.2 kW.
>>(In horsepowers: 1.1 kW = 1.5 hp and 2.2 kW = 3 hp)
>>
>>I think those numbers sound quite reasonable, but I think the real
>>numbers are still somewhat less. Maybe 1 hp or something.
>>
I`m quite convinced, that the force is quite a bit less than 10kg :
Try your bike : You won`t be able to put more that 20kg (at an 1 to 4 transmission,
which is common for many bikes) forward-bound force on the bike`s rear wheel.
Additionally you won`t be able to put your full weight on the pedals, so I think that a
calculation with 20 kilos on the pedals and thus 5 kg on the wheels will still be over-
estimated.
An then you surely have 30-50% loss of force (REIBUNG !).
So if you get to 3-4 kgs of pulling force on your bike your are already a real sports ...
(I think this resembles reality very well, because if you`re pulling another bike with
2 kgs you will be (approx.) half as fast as before.)
With this power, (without towing someone) you get to 30-40 km/h (36 km/h=20 kn)
Or try to be towed by a surfboard : You will realize, that there is no such thing like
10-20 kgs of pulling power on SurfBoards !
Scott Smith
a...@Informatik.Uni-Bremen.DE (Albert Wilkes) writes:
>I`m quite convinced, that the force is quite a bit less than 10kg :
>Try your bike : You won`t be able to put more that 20kg..
>Or try to be towed by a surfboard : You will realize, that there is no such thing like
>10-20 kgs of pulling power on SurfBoards !
My intuition tends to agree with this: windsurfers go fast more
because of absence of drag, not presence of power. Water drag is
minimized when on a plane, and wind drag is cancelled by the forward
force the apparent wind provides. And, remember you go faster until
forward forces are cancelled by drag forces...
In fact, this makes me think it might be possible to build a
human-only powered watercraft that could get on a plane. The major
design challenge is a lightweight mechanism to efficiently transfer
power from human to water. It would have to be lower-body, rowing
will never work because its upper-body. Plus the human and mechanism
would have to move back on the board as speed increased to lessen
surface area of the board on the water.
Scott
Michael Drews
guy I knew from Prineville, OR claimed to have waterskied on irrigation
ditches using a horse on the side for motive power. Rowing, propellers,
and water jets are not very efficient for moving boats. With two people
rowing with kayak paddles we could move a pontoon houseboat at about
0.5 mph. One person pulling with a rope walking along the bank could
move the same boat at about 3-4 mph. (About as fast as a 25 hp motor.)
Two people pulling with a rope could probably get a short board up on
plane. (Unfortunately the person on the short board kept running into
the dock.) It's amazing what people can come up with to amuse themselves
with when there are water, boards, and no wind ...
Michael Drews
--
----------
Obi-Wan: "The Force has power over weak minds."
Luke: "The Force has power over weak minds."
Pierre Jolicoeur
>but wouldn't be surprised if "4 times as heavy" means "4 times
>as much power required to move it at the same speed."
Are we talking about jet-ski type things? If so, the weight
difference could be more than 4.
>
>Third: it takes some energy to produce all that noise. Heck, even
>if a PWC consumed gasoline at a rate equivalent to 100 horsepower
>of power, I would (almost) believe that 90 percent of it went into
I'm not sure if you are serious here, but I think that the energy loss
in the generation of noise is negligeable. (probably less than .01%)[this
is a wild guess]... [can someone confirm that loss through noise is
very very small?]
Pierre
Adam Grant
Smith) wrote:
> In fact, this makes me think it might be possible to build a
> human-only powered watercraft that could get on a plane. The major
> design challenge is a lightweight mechanism to efficiently transfer
> power from human to water. It would have to be lower-body, rowing
> will never work because its upper-body. Plus the human and mechanism
I remember reading an article in some popular science type magazine
about a small human powered hydrofoil that looked like a bicycle. Only
the propeller and the foils were underwater when the vehicle was planing,
but at slow speeds it rested on a pair of pontoons.
Richard R. Thomas
On Wed, 23 Nov 1994, Richard R. Thomas wrote:
>
> Sails are not engines. Sails can produce air pressure differentials
> not horse power.
>
> Sails can be considered to be wind kinetic energy collector/converters
> when used as part of a moving system, ie. a sailboard system,
> (sailboard/rig/sailor).
>
> Sail size cannot be directly related to the "rate of work done" of a moving
> sailboard system because of the numerous other variables involved.
*************************************************************************
After reading some of the follow-up posts I think we have missed the plot.
It really is meaningless to relate sails to horsepower. This is the
reason why.
A good definition of Horsepower is "the rate of doing work".
The amount of work done would depend on the resistance overcome and the
distance through which this resistance is overcome.
For non-metrics, this value would be defined in foot/pounds.
Therefore WORK,(ft./lbs.) = Frictional Resistance,(lbs.) x Distance,(ft.).
So,
HORSEPOWER = Frictional Resistance,(lbs.) x Distance,(ft.) x Time,(sec.)
-----------------------------------------------------------
550
As stated before, a sail forms PART of a moving sailboard system.
VARY ANY OF THE ABOVE FACTORS AND THE HORSE POWER RATING WILL CHANGE.
* Note that the total weight of the system has essentially a vertical
component, (not a horizontal component) so its influence on
Frictional Resistance is small compared to its value.
* Frictional Resistance has an aerodynamic as well as the hydrodynamic
component. (How are you going to measure them?)
* The viscosity of the two fluids will also determine the Frictional
Resistance.
In-bedded with the sailboard system are active performance feedback loops.
These performance loops will also determine the Horsepower rating.
There are some other anomalies related to sails that need to be considered
in this discussion.
a: Identically sized and manufactured sails will give different Cd and Cl
figures due to the inherent unstable nature of the sail/rig setup.
b: Using a larger sail will not necessarily improve the Time-Distance
figures, (speed).
c: Sails of the same size can have very different s/elevation shapes and
cambers. Imagine the force variables involved with that scenario.
d: The peak rate of kinetic energy conversion for any apparent wind
velocity will be very dependent on the best AoA.
I hope this posting helps those who confuse the relationships between
Energy, Force and Weight with Horsepower.
Regards.
Paul Delnero
: In article <1707BC28...@vmd.cso.uiuc.edu>, EPL...@vmd.cso.uiuc.edu
: (Richard Engelbrecht-Wiggans) writes:
Possibly it is not the horsepower as much as the displacement vs planing
resistance of the board. When you are powered on your board/sail combo,
you are hanging much of your weight back and off the board and onto the
sail(wind). When you were holding that outboard(designed to push a
displacement hull to about 5-8 knots), you were placing much more of your
weight onto the board. Hence the ability to plane was inhibited and
without planing, the resistance of the hull secondary wake will limit your
speed to ~1.34 X (SQR-ROOT of Waterline length).
_____ See Ya...
_______ =-) PAD =-)
________ Paul Delnero
__________ Dublin, NH USA (pdel...@keene.edu)
rai...@mako.mugu.navy.mil
In article <Pine.SUN.3.90.941130...@tasman.cc.utas.edu.au>,
<che...@tasman.cc.utas.edu.au> writes:
> Path:
avalon.chinalake.navy.mil!newshub.nosc.mil!dog.ee.lbl.gov!ihnp4.ucsd.edu!munnar
i.oz.au!newsroom.utas.edu.au!news
> From: "Richard R. Thomas" <che...@tasman.cc.utas.edu.au>
> Newsgroups: rec.windsurfing
> Subject: Re: How much horsepower?
> Date: Wed, 30 Nov 1994 13:44:15 +1100 (DST)
> Organization: University of Tasmania, Australia.
> Lines: 84
> Message-ID: <Pine.SUN.3.90.941130...@tasman.cc.utas.edu.au>
> NNTP-Posting-Host: tasman.cc.utas.edu.au
> Mime-Version: 1.0
> Content-Type: TEXT/PLAIN; charset=US-ASCII
> In-Reply-To: <Pine.SUN.3.90.941117...@tasman.cc.utas.edu.au>
>
>
> On Wed, 23 Nov 1994, Richard R. Thomas wrote:
>
> >
> > Sails are not engines. Sails can produce air pressure differentials
> > not horse power.
> >
> > Sails can be considered to be wind kinetic energy collector/converters
> > when used as part of a moving system, ie. a sailboard system,
> > (sailboard/rig/sailor).
> >
> > Sail size cannot be directly related to the "rate of work done" of a moving
> > sailboard system because of the numerous other variables involved.
>
> *************************************************************************
>
> After reading some of the follow-up posts I think we have missed the plot.
>
> It really is meaningless to relate sails to horsepower. This is the
> reason why.
>
> A good definition of Horsepower is "the rate of doing work".
>
To summarize -- Windsurfing is FUN not work. Therefore, horsepower is the
wrong unit. Instead may I recommend that we use the unit smilepower (sp). Any
sail/board combo that creates a smile on your face has sufficent sp for the
current conditions. Any other measurment is meaningless.
Mike
Wayne Berthiaume
EPL...@vmd.cso.uiuc.edu (Richard Engelbrecht-Wiggans) writes:
> In article <Pine.SGI.3.91.941126044740.13524B-100000@x4u2>
> Volker Wedemeier <wede@x4u2> writes:
>
> >
> >rough estimate.
> >
>
> Also, I have a sliding rigger setup for my course board,
> and even though I can put out 1 hp for a short while--
> and have decent rowing technique--I can't come close to
> getting the board on a plane (at top rowing speed, the
> board feels--and its wake looks--exactly like what it does
> when slogging it out with a sail in very light air.)
> My top speed rowing a sailboard is about 6 mph for short
> bursts, while I can top 10 mph in a rowing shell; the
> sailboard must get up on a plane to go fast, and I am
> reasonably sure that doing so requires more than 1 hp.
>
> So...I believe it takes a bit more than 1 hp to push
> a sailboard 40 mph; the previous estimate of 1.5 to 3
> hp seems reasonable to me.
>
> Richard
>
Richard, you've neglected the upward component provided by the sail.
This lift helps to counteract gravity thus making it possible to use less
force to break the drag and get the board planning. While planning there is
even less drag to contend with; therefore, not as much power is required.
You should note the difference in power needed to maintain a plane is less
than to get the board on a plane.
-------------------------------------------------------------------------------
Wayne Berthiaume wa...@wally-gator.us.dg.com
"One man can make a difference and every man should try." -unknown
-------------------------------------------------------------------------------
Wilhelm Eickhoff
All this reminds me of a time many years ago when I fitted a
5 hp outboard to a Coleman canoe and went for a spin in it
all by myself. Frightened the .... out of me. The thing was
planing before I knew what was happening and only the drag
of the propshaft was keeping it's speed below the soundbarier.
Tried it only once, didn't like the noise.
( what ? no formulas ? )
Bill from Oz