i think you should draw a simulation... 1x1 cm grid on a sail, drawn in it's position according to the wind strength,boom, twist, freeleech.... for each sqare cm draw an arrow that hits the sail at certain angle... count speed of wind, density in try calculating how much force comes in at each square centimeter and when you get the force of each part of the sail, sum it up. when you got htis, you are able to calculate everything... if you make a program to do it, you win otherwise it is a whole lot of work...

I'm too busy and lazy to do this... then again, there is probably a much better way, but I only took basic physics and statics (the more detailed mechanics) for now at uni...didn't get to dinamics yet :(

I need to correct myself. Obviously I am not so much interested in mathematical formula but rough output numbers in kilowatts power for average windsurfer gear. Considering complexity of windsurfing rig straight physical calculations are useless ( or better said I don't want to bother you guys such with boring things on this forum) But knowing if we have mere 300W paddle board or 1 horsepower sail under our control to get us planing speed or 10 kilowatts dragster to reach magic 50 knots can be fascinating. I guess that some empirical approximation is possible and was done...

I seem to remember that we did the calcs before on here, and it turned out to be a couple of horsepower... so sideskirt seems right on the money

yep it was worked out,

then we got into a long debate about how 15knots in victoria is more powerfull then 15 knots in qld because of pressure at different temperatures.

i htink that just proved that qld sailors are faster

Excellent Sideskirt.

10knots=> P=1,221kW ==> 1,67Hp
20knots=>P=2,58kW ==> 3,52Hp
30knots=>P=3,84kW ==> 5,24Hp
(cit.)
That is good starting point.
I think estimates are close enough to reality.
I guess- because of turbulence flow , drag etc we are about as near as 50% to reality which is very good.
I propose then simple empirical experiment to verify and definitely put exact numbers.
If we can get our guinea pig on the windsurfing board and measure just three vector forces: at harness line, mast bast and foot rest at known wind speed - then we have at least one scientific factor. Name it: SurfFX :) (power output)
Considering your next sail purchase from Neil Pryde we can ask not only for Luff and boom numbers but also power output.
For those of you still in doubt: Do you think that all sails are equal- ie 7sm race cam sail has the same output as 7 m wave cam-less ?

So there's a linear relationship between power and windstrength?
I'm sure I remember from somewhere a logarithmic relationship, ie force varies with the square of wind strength.

sideskirt said...

also air density helps a lot... moisty air at same speed as very dry air gives more power :)

Are you sure? Moist air is less dense than dry air...

H20 in gaseous form has a molecular weight of 18, while dry air has a weight of around 28:
www.engineeringtoolbox.com/molecular-mass-air-d_679.html

And for total weirdness, you can improve the efficiency of a solar chimney by spraying warm water in at the bottom.

I don't think that relation is either linear or cube shaped .
Aerodynamics of our gear is so inefficient that plain simplified equation doesn't works better than long term weather forecast.
Simply put : if sailing boat could travel three times faster then actual wind speed than
at 50 knots Antoine Albeau should be sailing 150 knots not mere 49.09 at Saintes Marie de la Mer canal.
http://www.boardseekermag.com/special_features/speed/windsurfing-speed-record_061.htm
Anyway nobody bother to compare Lamborghini to Fiat Uno based on energy dispersed in fuel oxidation process because such data could be misleading. In some cases we can prove old junk disperse more energy then super car at same distance.

sideskirt said...

it is more of a comparison of mazda rx8 and ford mustang... mazda RX8 with 1,3L engine generates about 250Hp and mustang 3.7L engine generates 305Hp....

almost 3x larger engine volume but only 20% more power...

also: Wangl engine and Otto engine in another way of comparison of sails with cambers and without cambers :)

No because a rotary fires twice as often per rotation (essentially it is a 2 stroke).
Check FIA rules, the multiply rotaries' displacement but 1.8 or 2 or soemthing to get an equivalent displacement.

If you want to really look at power output, have a look at RC car engines at 600hp per litre

Anyway, back to sails.

It does not matter how much power your sail has because you can only use one sail at any given time. It does not matter what model you buy.
I used to buy powerful wave sails and realised I had been conned.
5.3 powerful wave sail, or 5.5 flatter wave sail. Same power in the same wind, so who cares what model you buy?
Sort of...

That is all fine on paper but not in real life.
Human being is fluid too and even glass is.
But for specific windsurfing gear computation is not that easy as for NASA space shuttle.
I regret that our airfoil is a bit less efficient that theirs.
Otherwise I will take a small trip to lower orbit say "hello!" to ISS and land safely on Runaway Bay. I guess my airfoil to mass ratio on my 7.0 Gaastra and / my 80 KG is not worse then shuttle / wings and belly