I was wondering if anyone has studied the effect of wind gradient for landsailing here?
dont quite know what you mean "studied" we have a dare wind indicator
whatyamaycallit here in Australia, someone with a camera maybe could post
a coloured photo........."studied",,,,indeed!!! 
I guess I should clarify more of what I'm after. I read a blog about wind surfing sail design and comment about twist on an AC72. Apparently there have been many studies mostly by water sailers about wind gradient. (that's the info I want to see)The important part of it is matching the apparent wind angles at the top of the sail as well as the bottom ie twist. To figure out twist you must first know how well your boat performs upwind and down wind in different wind strengths, what speeds it is capable of and what angles you are sailing to the wind. If you have that and know how much faster its blowing at the top of the sail as opposed to the bottom of the sail you can figure it out. Just wondering if someone here has any info on wind gradient studies. If found a few on the net but they are not exactly the same. Then again maybe wind gradient isn't the same all the time.
Thanks John
This might be a starting point.
cdn2.hubspot.net/hub/209338/news/Ad_aerodynamics/index.htm
There are many articles there that might be of interest, there are several books written by Czeslaw Marchaj.
en.wikipedia.org/wiki/Czes%C5%82aw_Marchaj
The AC72 is quite a radical beast, with a mast height of 40m (compared to 4-5m for a land yacht) and sail size of the AC72 of approx 580sqm (compared to 5sqm for a landyacht).
From the info I get is that 'wind gradient' is a sort of logarithmic scale depending on many factors including air temp, air density, surface resistance etc.
so is what your asking what shape/size should my sail be in class X for some particular windstrength for a particular surface type given my body weight is Z with a centre of body mass at my belly button( whichever side it has flopped to) and I am running a.oo x b wheels with hookworm tyres...............
basically we could discuss it at length but youll need to supply a few parameters for those of us who have been studying at length . we are certainly well beyond chopped up windsurfer sails at this point
Just trying to figure out if some twist is desirable for land sailing like it is for water sailing. For what I've researched 2 to 4 degrees of twist seem to be a good thing depending on how tall a rig is. I did some testing yesterday by taping my wind gauge on the top of my 520 mast looking at it with binoculars and lowering it at about a meter to see the difference. Most of the charts I've seen indicate the wind changes around 1.15 to 1.3 from those levels depending on how hard the wind is blowing. So if its blowing 10 mph at a meter it could be blowing 11.5 to 13 mph at 6 meters up. Add your point of sail and boat speed and you have twist from bottom to top. You can find twist by drawing vectors with the numbers and points of sail.
Simple answer, yes we did quite a bit of study in the early 80s relating to landyachts, along with the Auckland university windtunnel (who designed much of the rigs with Tom Schnakenberg).
I no longer have the figures, but it was quite clear that for landyachts, even with a 5 meter mast there is some consideration should be given.
Controlling the twist is something else again with a soft rig, and the big heads as used on windsurfers IMHO give too much for the speeds landyachts achieve. Likewise the simple triangles as many US yachts used to use don't give enough.
I do have some data and non tech discussions from Cogito the C Class cat which are interesting, but I do not think over relevant.
