Ok, so I've heard a few conflicting opinions on what effect camber inducers have on the performance of a sail.
I'm most interested in the low end power.
There was a thread a while back where the general consensus was that non-cammed sails were better for low end power because pumping worked better due to the sail being able to stretch.
However I have talked to a few other people and they say that cammed sails are better for low end power + pumping because they hold the foil shape. Pumping moves air over the foil which generates more power than a non-cammed sail because the cammed sail maintains a foil shape with higher lift.
The long and short of it is that I want a large sail for light conditions. It doesn't need to go fast, or be particularly stable. All I want is to get planing in minimal wind. Cams or no cams?
In my uninformed opinion which may well be wrong:
Go for cams (unless it's an Ezzy with heaps of shape already built in)
The idea of a sail is to change the direction of the wind. F = ma and all that, you want to accelerate the wind behind you, giving you a bit of a push forwards. The best way to do this is to gradually turn the wind using a foil, rather than a flat plate.
Cams make your battens stay the same full shape regardless of how much wind is pushing on them. Uncammed sails belly out more the more wind they have (which is pretty much the opposite of what you actually want them to do).
However, cams will mean that the sail is heavier, the bigger luff pocket will make it harder to fly the sail when waterstarting or uphauling, and it's harder to rig.
But I like my 6 cams on my biggest sail, and zero cams on my smallest 
quote:
Originally posted by DL
The long and short of it is that I want a large sail for light conditions. It doesn't need to go fast, or be particularly stable. All I want is to get planing in minimal wind. Cams or no cams?
quote:
Originally posted by nebbian
In my uninformed opinion which may well be wrong:
Go for cams (unless it's an Ezzy with heaps of shape already built in)
The idea of a sail is to change the direction of the wind. F = ma and all that, you want to accelerate the wind behind you, giving you a bit of a push forwards. The best way to do this is to gradually turn the wind using a foil, rather than a flat plate.
Cams make your battens stay the same full shape regardless of how much wind is pushing on them. Uncammed sails belly out more the more wind they have (which is pretty much the opposite of what you actually want them to do).
However, cams will mean that the sail is heavier, the bigger luff pocket will make it harder to fly the sail when waterstarting or uphauling, and it's harder to rig.
But I like my 6 cams on my biggest sail, and zero cams on my smallest
As always I disagree with Gestalt. Big sails with cams built for light wind have far more draft than a non-cammed sail. If the non-cammed sail was to attempt to achieve the same it would be baggy as a bag of wotzits, which is just wrong.
Where non cammed sails are good is with pumping.
Traditionally the most powerful bottom end sails built for getting heavier people and boards on the plane have been 2-3 cam sails.
Think I agree with mkseven, although I haven't had a huge experience with cambed sails. They have full shape at 0 wind, (well in theory, if they're good sails, more wind shouldn't be able to increase their shape)
As before said non cambed sails need some wind to turn them on.
The trouble here is how much wind????
Some sails fully rotate and shape up with about 5kns others seem to need more like 15-20kn to get full shape. If you have the later I'm sure it won't be much good in light winds.
This is probably another area where mast compatibility plays a roll
quote:
Originally posted by 555
Sounds like some slightly dodgy aerodynamic theory there Nebs! Bernouli's theorem is that if you make air move faster, it's pressure will decrease. That's why our sails have that curved foil shape - the air travelling over the bulged side of the sail has to go further than the air on the inside, which means that it has to go faster to meet up again after the sail has passed through..
A bit off topic.... no.... yes......no ?
Mentioning pumping: remember that half (or more) of the effect is due to loading the fin briefly to create more lift and help the board lift up. Also (on a wve / freestyle board) rocking it back on its rocker to stop it from pushing so much water up front.
Not all of it is about the sail...
Anyway back on topic.... cammed.
quote:
Originally posted by DL
Ok, so I've heard a few conflicting opinions on what effect camber inducers have on the performance of a sail.
I'm most interested in the low end power.
There was a thread a while back where the general consensus was that non-cammed sails were better for low end power because pumping worked better due to the sail being able to stretch.
However I have talked to a few other people and they say that cammed sails are better for low end power + pumping because they hold the foil shape. Pumping moves air over the foil which generates more power than a non-cammed sail because the cammed sail maintains a foil shape with higher lift.
The long and short of it is that I want a large sail for light conditions. It doesn't need to go fast, or be particularly stable. All I want is to get planing in minimal wind. Cams or no cams?
plenty of dodgy aerodynamics going on in this thread. Air does not meet back up at the trailing edge, smoke tests of foils prove this. nebbian pretty much has it right I reakon. people argue newton (f=ma) or bernoulli, or even more ridiculously percentages of both to explain lift. Both are ways of describing the same thing, one by conservation of momentum one by conservation of energy. By some mathematical trickery they can be shown to be equivalent.
In my opinion cams are desirable on big sails where you want all the lift you can get but less desirable in smaller sails as you have stacks of lift and what you want is instant control by powering and depowering the sail, cammed sails are less easy to depower.
quote:
Originally posted by PhilJ
plenty of dodgy aerodynamics going on in this thread.
Thought for the day:
Would a reflexed sail provide less turning moment, so therefore allow the use of a smaller fin, which in turn would allow you to go faster?
quote:
Originally posted by nebbian
Thought for the day:
Would a reflexed sail provide less turning moment, so therefore allow the use of a smaller fin, which in turn would allow you to go faster?
So, cams are best for low end, light wind power?
Would a Severne Overdrive be a good choice?
. so how many 9.5m plus race sails without cams have you used? i've used a couple myself form different manufacturers.
Don't know or particularly want to get excited about aerodynamics. I have tried and have both types of sails and from my understanding in ideal conditions for the average windsurfer either type will give similar performance.
The big issue comes when changing conditions kick in. I sail on the river and there can be patches of lull in between the good stuff. With the cammed sail, it holds its shape through the lull and doesn't flatten (it basically keeps the shape you have set it too). With a no cam sail you would have to bag it out a bit to handle the lulls and then it would be overpowered in the windy bits.
Size for size, I don't notice any difference when water starting or flipping on a gybe. Then again I use Tushy Lightnings, which only have 2 cams and have a luff pocket which is no bigger than the equivalent no cam (T3).
OK Gestie, go get you're 9.5m wally sail and I'll see you on the water.
I'm was not talking about race sails, i'm talking about the power planing sails.
If you want a long board sail for sub planing winds, then yes choose the wally sail anyday.
You're absolutely correct draft is shaped into the sail not just by battens. Cams help static draft however, most modern no cams require a bit of wind to push the draft into shape. It may not be much but also consider bottom end also when you sail into a lull and the shape drops out of the sail a bit. No batten soft sails require less wind to fill so they are the ultimate in light wind.
You also mention tight leach which has nothing to do with cams or battens, put a tight leach on a cam sail and you get the same power effect. Rig a cammed sail with no downhaul and enjoy you're trip to the physio the next day, but at least you'll be moving early on the water.
Stupid me for always associating bottom end requirements with planing, I guess that is because you come from longboarding background. How many races did you win on the no cam sails in light winds?
There is truth in both camps, flip a coin and let you're sailing do the talking 
wally sails are only 6.5m
Avoiding all technical bizzo, I've got a 7.5 (3cam) Gaastra GTX, love it!
Dunno about the guys at the shop's intentions, selling it to me as my first sail, but on light-medium days, it's great.
The rigging is supposed to be more difficult, but...(here I go, I said no tech. crap......) the cams 'create' the sail's shape, leaving the guesswork out of rigging, although the outhaul tension must be right, otherwise you look like a 'dill' trying to 'pop' the sail after a turn. The only downside I find (mentioned earlier), is when waterstarting in gusty conditions it's touchy, but that could be just my lack of ability showing!
I find it interesting that there is so much contradiction in opinions as to what effect cams have on early planing.
Maybe this is because it is not about the cams, but more about other aspects of the sail?
Big sails are better for early planing because they catch more wind.
Big sails are less stable because they are "big"
Therefore, big sails tend to have cams to increase stability.
So it would stand to reason that most light wind sails have cams solely because they are big, not because cams are good in light winds.
Maybe the question of "do cams help early planing" is as misleading as asking whether red sails go faster?
Its simple - may I be so bold as to say "if you are planing, cambers are faster in pretty much all conditions", assuming everything else being equal.
If they weren't they why are they in the biggest race sails and in the smallest speed sails?!
from what i have found most modern cambered sails have very open leeches which gives them great top end but the down side is that low end power is reduced and the ability to pump the sails in marginal condition is also reduced. Cambers on most sails exert pressure onto the mast which 'forces' shape into the sail which is why the draft position is held in place better than 'raf' sails. So if you are looking for a sail with better bottom end look for something that has a tighter leech .
Does anyone have information on the weight of the Severne Overdrives?
It doesn't seem to be published on the Severne website.
