Old Nick ) writes:
On 1 Nov 2003 13:28:49 GMT, (William R.
Watt) wrote something
......and in reply I say!:

Bill....if I may address you as such...

You ask for power formulae for a _sail_...then argue?

clarify. some responses did not address the question.
you can go back and re-read the original question if you like.

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William R Watt National Capital FreeNet Ottawa's free community network
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I scaned diagrams of a possible sprit sail and put them on my website. So
far I just use the wetted surface and displacment to determine the sail
area. I still have more calculations to do for it. There's a sail cutting
diagram too. To use as much of the sail material and to keep the centre of
effort low I did not follow the recommended proportions in John Leather's
"Spritsails and Lugsails". I drew a sail more like older less efficient
sprit sails. BTW if you chose the length of the foot and leach then you
can use Leather's proportions to find the head and luff independent of the
mast length, although he relates them all to mast length. Maybe I'll
describe that in the design text later.

the diagrams are at www.ncf.ca/~ag384/Solo15.htm. I won't link it to my
home page until its finished which could be quite a while yet. Its still
very rough. I'm spending as much time trying to figure out how to use the
computer as I am trying to work out the design of the boat.




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William R Watt National Capital FreeNet Ottawa's free community network
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On 2 Nov 2003 16:09:57 GMT, (William R.
Watt) wrote something
.......and in reply I say!:

Old Nick ) writes:
On 1 Nov 2003 13:28:49 GMT, (William R.
Watt) wrote something
......and in reply I say!:

Bill....if I may address you as such...

You ask for power formulae for a _sail_...then argue?

clarify.

A sail cannot be quantified. Too many variables.

some responses did not address the question.


hmmm... they may not have _answered_ it....

you can go back and re-read the original question if you like.


No need. AFAICS, the reason there is such a spread is that conditions
apply.
************************************************** ****************************************
Until I do the other one,this one means nothing
Nick White --- HEAD:Hertz Music

remove ns from my header address to reply via email

!!
")
_/ )
( )
_//- \__/

On 1 Nov 2003 13:28:49 GMT, (William R.
Watt) wrote:


no, there's got to be a formula relating wind speed, sail area, and
horsepower.
--

Such a formula could be generated, In fact, a vast family of such
formulas could be generated, all equally valid, and all giving
different results.

The assumptions required to generate such a formula swamp any results
that might be derived from it.


Rodney Myrvaagnes NYC J36 Gjo/a

"Religious wisdom is to wisdom as military music is to music."

Rodney Myrvaagnes ) writes:
On 1 Nov 2003 13:28:49 GMT, (William R.
Watt) wrote:


no, there's got to be a formula relating wind speed, sail area, and
horsepower.
--

Such a formula could be generated, In fact, a vast family of such
formulas could be generated, all equally valid, and all giving
different results.

The assumptions required to generate such a formula swamp any results
that might be derived from it.

yes, but that's true of most things in nature and yet applied mathematics
works. for example, formulae are used to design aeroplane wings. the two
approaches used are to make the most appropriate assumptions and verify by
testing. the results only have to be accurate enough to be effective
design tools.






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William R Watt National Capital FreeNet Ottawa's free community network
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William R. Watt wrote:

yes, but that's true of most things in nature and yet applied mathematics
works. for example, formulae are used to design aeroplane wings. the two
approaches used are to make the most appropriate assumptions and verify by
testing. the results only have to be accurate enough to be effective
design tools.

I don't know that that is a valid comparison. Aerodynamic formulas for
aircraft calculate the amount of horsepower required to overcome drag
and provide lift but that is not what you are after. Also aircraft
foils operate in a very limited angle of attack and with predictable
wind speeds.

If a single horsepower factor for a particular sail area/wind speed
existed the polars developed from VPP programs would be circular. You
can't take a single horsepower and compare it to the horsepower
delivered to a prop. The propeller delivers all its power in one
benificial direction. Wind force on sails has a lift and drag component
and the net benificial power varies depending on the direction of the
lift to the relative heading you want to steer. That is constantly
varying. You might determine an equivelent horsepower for one wind
speed and one aparent wind angle but it would be valid for only that
condition.

--
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 3 Nov 2003 13:54:29 GMT, (William R.
Watt) wrote:

Rodney Myrvaagnes ) writes:
On 1 Nov 2003 13:28:49 GMT, (William R.
Watt) wrote:


no, there's got to be a formula relating wind speed, sail area, and
horsepower.
--

Such a formula could be generated, In fact, a vast family of such
formulas could be generated, all equally valid, and all giving
different results.

The assumptions required to generate such a formula swamp any results
that might be derived from it.

yes, but that's true of most things in nature and yet applied mathematics
works. for example, formulae are used to design aeroplane wings. the two
approaches used are to make the most appropriate assumptions and verify by
testing. the results only have to be accurate enough to be effective
design tools.

I am tryng to be helpful. The noise in the set of reasonable
assumptions will produce output noise many times the size of the
signal. An airplane wing is used in one medium away from boundaries.

You could empirically derive some formula from the performance of a
rogallo type hang glider well off the ground. It would, however, be
close to useless for predicting a sailboat's behavior in the real
situation of a water/air boundary, with its normally height-dependent
wind-velocity vector.

I hope the next questions don't offend.

How skilled a sailor are you?

Can you enter a local club one-design race and be fairly sure you
won't come in last?

Have you ever felt the difference a new sail makes?



Rodney Myrvaagnes NYC J36 Gjo/a

"Religious wisdom is to wisdom as military music is to music."