Is a new sail flat?

Not sure about readings on line but unless its a furling main then it must, and would usually, have shape to it. Furling mains are flat so as to stow correctly and the "shape" to the sail would create a problem as the mast would need to be cavernous to accept it. Beyond that, with normal sails they need a profile to create the correct aerodynamic properties.
 
I can't think of any sail that would be designed to be completely flat. All sails will be designed to have some shape. Think (very roughly) of the top of an airplane wing. They are designed to be aerofoils. Spinnakers will, of course, have even more shape.

As they get older, dacron sails in particular will become baggy. The camber in the sail will increase, and move aft. They will become less efficient and will tend to make the boat heel rather than drive he forward.

Lots of books on sail shape, though I don't have one to hand to recommend.

Maybe try the North Sails website, or another sailmaker.
 
It all depends.

The sail designer will either have a brief in his own head, or one that has been given to him by the boat designer or by an owner, or if it is a classboat used for racing there will be rules on sail construction which might dictate how much fullness is allowed in the sail on construction.

When I ordered a set of sails for my Enterprise dinghy many years ago I was asked what kind of sailing I did..well racing obviously, but more specifically did my regular sailing take place on the sea, rivers or lakes/reservoirs. If you are a sea sailor you will want a flatter (which is a relative term) sail than if you were racing on the Norfolk Broads, where light winds dictate a fuller sail will generally work better, but which will be difficult to de-power if the wind suddenly get up (on a yacht you would reef, on a dinghy you would use the kicker and the cunningham to flatten and depower)

All dacron type sails stretch (unlike the cotton ones I started sailing with..which shrink), so over time and hard use your new flattish sail will become fuller, but not necessarily in a good way as the fullness may not appear in the optimum position for fullness to be usable. It may just lead to your boat being overpowered without being able to control it by flattening the sail (an alternative to reefing in rapidly changing conditions)

When a sail becomes completely baggy, and it is old and well used, then there is the possibility that it is 'blown out' which means that it has stretched beyond the point where it is possible to get an aerodynamically efficient shape out of it. This happens a lot quicker with the poorer quality sail cloths you sometimes see that are thin and highly resinated (shiny) to keep their shape. If the sail is otherwise of good quality and good condition you can get it recut and the bagginess removed, but you have to weight the costs of that up against a new sail, and how long the recut sail is likely to last.

Tim
 
davidpbo said:
I have old sails which appear baggy.

When a sail is supplied new is it flat ?
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No. Almost certainly not. If it's made of good, decent woven stuff like terylene or cotton, the panels will have been cut so that it can't be laid out flat. Take a sheet of A4 paper, cut it in half, trim the two cut edges to be slightly convex, sellotape together again, that sort of thing.

Fancy laminate things can be made to have more subtle continuous curves in them.
 
I think what you're getting at, is sails are generally ( a wild generalisation but you get the gist ) supplied on the flatter side - while of course keeping an aerofoil 'wing' shape - and in my view that's what one should specify for a seagoing boat - as during their life they will slowly but surely become fuller.

A short term answer to full sails is an adjustable clew outhaul as on dinghies, it's surprising how few cruisers have this; combined with the slightly out-dated 'flattening reef'* or a cunningham style downhaul a few inches above the tack it will help but not cure a baggy sail.

* There was a period in the late 1970's when 'shelf foot' mainsails were tried; they were a baggy disaster.

The only real answer is to buy new sails more often than most people like to; they are after all the whole raison d'etre of the boat, a lot of people are happy to pay for engine replacements but ignore their sails...I know, as I crewed a racing boat with 15 year old sails, against people who were sponsored and considered a sail very old at 6 months !
 
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davidpbo said:
I have old sails which appear baggy.

When a sail is supplied new is it flat ?

Any simple reading on the subject on line ?

Thank you.
Click to expand...

A flat sail is as much use as a chocolate fireguard.

All sails have a designed shape as new. They can vary, a good sail maker will talk to you about what you want and can vary the sail shape accordingly. For racing sailmakers the amount of technology behind the design process is significant.

On a racer you could have a light, medium & heavy #1, each of pretty much the same sail area but of different weight and cut to suit different wind ranges.

On one boat we had to move the mast step to change between the two mainsails. They were from different sailmakers and the difference in the cut was noticeable (for racing anyway).
 
I have a new suit of Dacron sails. The loft told me they build Dacron sails flatter than the optimum, in anticipation of subsequent stretch, whereas they build laminate sails fuller than the optimum, in anticipation of shrinkage. Mind, they're only talking a percent or two, so barely noticeable to the average Joe.
 
bbg said:
I can't think of any sail that would be designed to be completely flat. All sails will be designed to have some shape. Think (very roughly) of the top of an airplane wing. They are designed to be aerofoils. Spinnakers will, of course, have even more shape.

As they get older, dacron sails in particular will become baggy. The camber in the sail will increase, and move aft. They will become less efficient and will tend to make the boat heel rather than drive he forward.

Lots of books on sail shape, though I don't have one to hand to recommend.

Maybe try the North Sails website, or another sailmaker.
Click to expand...

Adding to the above, new sails specified for cruising will come with a measure of camber. For performance sails the camber will be less, but never flat as they will otherwise fail to drive on the wind when tightened up.

But after a couple of seasons the camber shakes out, wind and sun wreaking their damage on the structure. No amount of halyard and sheet tension will completely overcome this.

For almost all points of sailing, other than fine on the breeze this is of little consequence to cruisers. Having just installed a new main, I can attest again that a new stiff main drives considerably closer to the breeze. But after a little while, that will fall off again. Alas! Who can afford new sails every 3 years?

PWG
 
But recutting is cheap...and cheerfull

I had my old sails re-cut this spring by a local sail loft, both the rolling gennie and the main. Fantastically changed the gennie, which wouldn't even roll properly before as she was so baggy. I think the main could have used even more cut from her, but as the entire operation only cost me £150 or so I'm not complaining.

The simple answer is if you are getting new cruising sails, I would suggest that you make the jump in price to get sailcloth that has Dyneema/Kevlar/Spectra etc. woven into it. This differs from cruising laminates (which are sandwiches of materials), as it is more like a crossed web of Spectra cords running through the cloth, so it has less tenancy to de-laminate, or to stretch compared to Dacron. Hood, North Sails, Sanderson (using Hood cloths) and most of the others will all sell you such sails for cruising. They have MUCH less stretch than Dacron, and when I checked prices this summer they were not that much more expensive (several hundred pounds, not thousands) than plain Dacron - most of the money is in the fabrication and cutting of the sail, not the cloth.

Having said that, such cloths are stiffer and can be more difficult to flake on the boom, and more difficult to unjam if you get a batten stuck in a lazyjack. But their _effective_ lifespan is so much longer than simple Dacron that it is probably worth the hassle. And they are claimed to be longer lasting and cheaper than cruising laminates, although they will not be as high performance. Good middle ground it would seem.
 
It is all down to the construction of the sail cloth. A normal woven dacron cloth is a woven cloth with the warp going along the cloth and the weft going across (I may have that the wrong way round) The point is that the cloth is very resistant to stretch along the strands but pull it on the diagonal (bias) and it stretches like mad. To reduce this stretch the cloth is basically covered in filler which stops the fibres moving. Alos the sail maker cuts the sail panels so that the strain lines go along the fibres rather than on the bias. This is why a cross cut sail the panels should perpendicular to the leech rather than horizontal.
Higher quality cloth such as Hoods cram far more fibres into the weave to reduce the movement, reducing the need for filler. This leads to softer more long lived sail.
As soon as a sail gets used the filler starts to crack (you see a light marbling effect on the surface) and eventually fall out. This allows the sail to stretch and become baggy. At this stage the best thing you can do is throw it away and buy a new one. Spend more on a better quality cloth and it will delay this time. Sails made from cheap sailcloth do not last as long as ones made from expensive cloth.
Laminate sails are a different technology altogether where they keep their shape really well until they suddenly fall to bits as the laminate fails.
 
Lakesailor said:
Hmm. So my main, made before 1976 will be past it's best then?
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Just possibly. I threw a Genoa stamped 1976 in the skip last year, the new one is awesome. Even better is this year's new main which is definitely not flat. You don't really realise how **** an old sail is until you compare it with a brand new one. Interestingly, the new main is very sensitive to correct halyard tension, unlike the old which would only set properly with the halyard cranked on fairly vigorously. The new one is very easy to over-tension on the luff.

PS Edit: I can't believe the forum software censor objects to a word describing something as fit only to be dealt with by a renderer of deceased equines.
 
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Try some more words and be amazed.
I think Mormons have taken over the Forums.

Strange thing is the main sets well and I can still sail at hull speed and better. It has started fluttering between the battens and the fulness is a bit more than I would like.
On the other hand, for short day sails on a lake it does the job.

That Jeckells Logo changed in 1976

Aug14_3.jpg

But you can see it's getting very frail toward the leech.

seahawksail3.jpg
 
Old sails

My guess is that the op is looking at old sails and wondering if new sails would work better. ie worth the cash. The answer is probably much better especially going to windward in a stiff breeze.
Dacron/polyester does stretch under use. As said this can be adjusted for mainsails but not so easily for jibs.
I think a new jib for strong winds if you use hank on or new jib for furling will make a lot of difference to pointing ability. Not so important in light winds when you want some shape.

I think the way a sail; maker will assess a sail is to stretch it out horizontally from 3 corners and look at and measure camber (baginess) produce by gravity. Or in actual use you can photograph the sail for measurement and assessment. Or if you are a dummy like me buy a new one and hope for improvement that justifies the cost.
I am on my 4th set of sails or is it 5th set.(30 yrs) especially for (hank on) smaller jibs a new sail always gives better performance especially for jibs in stronger wind. olewill
 
Lakesailor said:
Strange thing is the main sets well and I can still sail at hull speed and better.
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I'll tell you now, that sail is not "setting well"....

As with the debate between dacron and laminate, the advantages of a new sail are often misunderstood.

Your new sail is unlikely to make you go faster on a reach or a run.

Your new sail WILL make you point higher, and heel less, upwind.

If all racing was point to point reaching, all sails would still be dacron. Racing owners spend the big bucks to get to windward.
 
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