Good morning,
I would like to know wether a chart with the following axis exist
on one axis, there is the wind speed,
on another axis, there is the sail size/surface,
and, in between, there will be the corresponding weight or tension on the sail (in lbs or kg) due to the wind speed
Has anyone come accross that type of table before? If so, where can I find it?
Mu! There are a many more factors than just wind speed. You will need a multidimensional graph, and even then it will be impossible to correctly account for sail design variances and individual preference. Trial & Error is your friend.
I've seen a formula somewhere that has force on one side and wind speed on the other.
But a sail is more complicated than that, it's foil produces lift, that needs to be taken into account as well I think.
Just googled this, if it's any use?
In the meantime, I found this
F = 1/2 * air density * (wind speed) ² * Aerodynamic coefficient * Surface.
If wind speed is 20 m/s and the sail surface is 6.4, then I get
= .5 x 1.293 x (20) ² x 1.1 x 6.4
= 0.5 x 1.293 x 400 x 1.1 x 6.4
= 1820 newton = 185 kg or 407 lbs
not sure about the drag coeficient, you chose 2, I chose 1.1. found conflicting information about what to select.
I am doing this to know what rope / cord strenght I should use (what tensile in lbs or kg) ? and if I need to do several loops/rounds when I attach the sail to the clew with the rope. I am trying to shorten the time I spend riging my sail.
maaaaaate...just loop it round once and yank it out...any length of outhaul rope will be fine..go to your local shop and get a length....spend more time sailing than worrying about formulas and stuff.....
You are not going to break any decent outhaul/downhaul rope at the clew (unless its old and worn.) If you are so worried then get some marlow formuline which lasts 10x that of normal braided dynema in my experience. I used to replace my downhaul rope about 5x per year until I got some formuline, never had it snap and rig big race sails for 100+ sessions per year and it has lasted 2 years (I should really replace it but it shows no sign of wear)
Yvan, talk to the other guys where you're learning, listen, watch and learn. Also Redsurfbus is on the money re line 
cheers firiebob!
Another thing I thought of was dont focus on these forces. The outhaul and tension of a sail is a 'feel' gained from experience.
As a quick guide - if you are placing your boom clamp mid cut out then the sail printed stting will often be correct (not always), placed higher to the top of the cut out, add a couple of cm to the extension on the boom.
If the sail feels twitchy then you have too much outhaul on, but will go upwind very well. If it feels slow to plane and heavy you may have too little outhaul on, this can be shown as the sail will touch the other side of the boom when powered up (this is called negative outhaul and used by speed sailors when bearing off the wind).
The best thing for you to do is set your sail and spend a session adjusting the outhaul from max to mid to min in a constant wind, this will give you an idea of the different feel that the sail gives at different settings.
As for rigging, I race with people who use only 1 line of rope through the clew eyelet and nothing more, as part of adjustable outhaul setup. I prefer a double line through the eyelet. Some booms have a loop and go set up (http://www.k-bay.co.uk/_product_43824/Alloy_Tail_Piece_62cm_-_Standard), rather than pulleys there is a hole that the line comes from, a cleat and a 'rimmed catch' (cant think of what to call it) on the other side of the mid point. All you have to do is put the loop through the clew and over the catch, then tighten by pulling more line through the cleat........takes seconds to rig the outhaul this way.
