Battens - what do they do?

[knuterikt]

Yes. Or indeed if you gained the same SA with a longer luff (P) and the same boom length (E).

For the same sail area with a larger roach you've got a greater effective SA.

The reason is you get tip vortices from the top of the sail. One way of thinking about that is that it negates a large part of the area of the head of the sail. There's a good diagram in one of CA Marchaj's books that explains it very well - probably dodgy to photocopy it and attach it but Fig 75 on P93 of "Sail Performance" if you can get a copy from the library. All books on aerohydrodynamics of yachts should describe it in a good level of detail though. I've flicked through Fabio Fossati's book but could find such a suitable diagram.

Thanks for the explanation.
I got curios because I don't think that NOR rating http://www.norlys.org/ use information about battens when calculating the rating.

NOR rating (formerly NOR lys) started to use the ORC VPP system this year, and It does not look like ORC have any information about battens in the database.
But the sail measures give numbers for the roach in the way they are taken.

 

[Chanquete]

The main objective in sail aerodynamics is to obtain a sail profile with the minimum drad and the largest lift (considering the projection of the attained lift in the sailing direction.
One important drag component is the induced drag. Withouut entering in detail this drag is a result of the vortex system created by the sail.
It has been found long ago, that an ellyptical lift distribution along the sail minimizes this drag.
It is also known that the classical triangular planform of older sails exhibits large induved drag values.
I dont mean that a pure ellyptical shape of a sail is mandatory but it is very useful to respect more opr less this concept.
In fabric sails battens are indispensable to mantain a nearly ellyptical shape.
Other drag contributors are uncontrolled wing fluctuations. I dont mean the controlled beating of bird wins.
Battens rigidizes wing shapes.
With our present knowledge this is an acceptable solution.
In the feature sails with controlled flexibility may change the panorama.
Under a particular wind intensity turbulence characteristis and the dynamic behavior of a boat in particular sea conditions the flexibility characteristics of battens can improve or worsen the performance of a sail.

 

[Tranona]

The problem is that a new mainsail (which I could do with) is going to cost a lot of money so I don't want to take a chance on gettiing it wrong.

You are unlikely to get it "wrong" if you follow the advice of your sailmaker. Battens are pretty much the norm, for good reason. The real debate is whether you stick to the conventional short battens, go the whole hog and have full length battens and batten cars, or as is increasing common 3/4 length battens. A good sailmaker will cut the sail to maximise the performance of your chosen configuration and your boat.

 

[lpdsn]

Thanks for the explanation.
I got curios because I don't think that NOR rating http://www.norlys.org/ use information about battens when calculating the rating.

NOR rating (formerly NOR lys) started to use the ORC VPP system this year, and It does not look like ORC have any information about battens in the database.
But the sail measures give numbers for the roach in the way they are taken.

It's not the battens per se that are handicapped, but obviously you need battens to support the roach.

Here's how they measure a mainsail for IRC.

http://www.ircrating.org/images/stories/pdf/measurement/measurement_mainsail.pdf

As I said, it is a secret formula how they use that to calculate the rating, but you can see the focus on roach.

 

[Iain C]

They improve sail shape, and support the loach of the trailing edge, where it curves outside the straight line drawn between head and tack corners. A fully battened main allows full control of the sail shape. In mast reefing means a flat loach and less efficient sail, so is a trade off for convenient sail storage and handling.

Racing boats don't use furling sails at all, and will have carefully designed battens and profiles to optimise performance, especially to windward, where the ability to point higher and faster is King.

A loach...

A roach...

Hope this helps ;-)

 

[AngusMcDoon]

Well it should be called a loach because then it goes with luff and leech.

 

[charles_reed]

Battens are for junk rigs really. A clever one part sheet to all their ends and you have a succession of booms rising to the sky. Hoist and lower regardless of attitude to the wind. Such a quiet sail - never any flapping. Climb up the windward battens to look for coral heads and Lepe Spit. No stress in the sail - it cannot blow out or rip past a batten and so on.....

So beautiful to behold and fast and maneuverable. Long live the fully battened sail.

An interesting idea!
The junk rig has been around since the 12th century - the bermudan rig is only about a century old.

I'm assuming the OP was confining his remarks to the Bermuda rig. Otherwise we'd have to start mentioning C A Marchaj and his (at least 3) books on the subject of sails.

 

[chrisedwards]

12th century BC. All gone now - even the knowledge.

An interesting idea!
The junk rig has been around since the 12th century - the bermudan rig is only about a century old.

I'm assuming the OP was confining his remarks to the Bermuda rig. Otherwise we'd have to start mentioning C A Marchaj and his (at least 3) books on the subject of sails.

 

[Babylon]

No - I'm not sure at all. Which is why I welcome the opinions of others, especially of anyone who has a battenless Bermudan mainsail.

I know that the famous cruising yachtsman Eric Hiscock preferred not to have battens and the author of 'The Sailaker's Apprentice', Emiliano Marino, doesn't like them. Apart from those two I can't find any other references to battenless Bermudan mainsails.

Les Powles didn't like them either, I think mainly because of his experience of breakage on long ocean passages:

http://www.amazon.co.uk/Solitaire-S...UTF8&qid=1376732643&sr=1-4&keywords=solitaire

 

[Babylon]

Thanks for all the very interesting input.

Now to elaborate the question: with full or 3/4 length battens, is one still able to tweak the sail according to sailing conditions - ie flatten the sail in higher winds, move the draught forward or aft to maintain drive, etc?

Or, as an earlier poster said, is it all binary - either ON or OFF?

Or have I misunderstood something?

 

[lpdsn]

Les Powles didn't like them either, I think mainly because of his experience of breakage on long ocean passages:

IIRC, RKJ broke one or two of his the last time round, but I don't think he considered getting rid of them entirely.

 

[charles_reed]

Thanks for all the very interesting input.

Now to elaborate the question: with full or 3/4 length battens, is one still able to tweak the sail according to sailing conditions - ie flatten the sail in higher winds, move the draught forward or aft to maintain drive, etc?

Or, as an earlier poster said, is it all binary - either ON or OFF?



Or have I misunderstood something?

Well I do use mast bend on my fully battened mainsail, but it's not quite as effective as it is with a radial cut short-batten sail.

Round section battens do have a reputation for breaking more easily than flat one and certainly breakage of old-fashioned birch battens was commonplace and the resultant tear an unnecessary risk to take for ocean sailing where getting the final 1/2 knot is not a consideration.

 

[AngusMcDoon]

I've had 1 of 10 full battens break in 30k miles of trimaranning. They get transferred from one mainsail to the next as they aren't cheap (£600 for the set). They are Fiberfoam tapered composite rectangular cross section.

http://www.fiberfoam.net/

 

[lw395]

Thanks for all the very interesting input.

Now to elaborate the question: with full or 3/4 length battens, is one still able to tweak the sail according to sailing conditions - ie flatten the sail in higher winds, move the draught forward or aft to maintain drive, etc?

Or, as an earlier poster said, is it all binary - either ON or OFF?

Or have I misunderstood something?

A good fully battened sail can be well flattened by mast bend, the Cunningham still works etc etc.
The digital on/off refers to the tendency for the sail be less willing to drive on the bottom half while the top half flogs.
It depends whether you have a well designed rig, or a FB sail chucked on a mast not ideal for it.
For a cruising yacht, I would expect the outhaul to be critical, the FB main should be fairly flat with it cranked on, not too reliant on mastbend.
When reefed it should have a good shape, perhaps 7% draft?

 

[dunedin]

A huge number of racing boats - top end dinghies, yachts and cats - use fully battened sails, so yes you certainly can tweak the shape appropriately.

No racing boats that I am aware of do without battens (except perhaps those with wings and no sails!). The rare exceptions being one-designs originally designed for other purposes, notably the Topper raced by thousands of junior sailors, where battens were not fitted so the sail could be rolled up round the mast and the boat dumped on the beach - and getting a decent racing sail shape in a Topper is a nightmare as a result.

Since reading the various threads on furling mains vs conventional battened ones, we have been keeping an informal observation now for circa 5 years. In all that time I am fairly certain we have never once been overtaken upwind by a boat with a furling / un-battened main sail, irrespective of boat size. Quite a few battened laminate sails have passed us though, going higher and faster. Currently we have a Dacron mainsail with one full batten and the rest normal sized, which seems a reasonable price / performance / durability balance. A 12:1 Cunningham control and adjusting this regularly is important though, as well as a 36:1 main sheet fine tune helps.

 

[chrisedwards]

Laminates? The junk rig Westerly Longbow which outclassed so many "faster" boats on the RTI just used scaffold poles for battens.

 

[charles_reed]

Laminates? The junk rig Westerly Longbow which outclassed so many "faster" boats on the RTI just used scaffold poles for battens.

BUT, junk rigs are totally different to bermudan. Not only do the battens develop the aerofoil, but they are essential for the reefing process - the heavier the better.

In response to breakage of battens, I've never had a GRP one break, though it was a matter of course with early wooden ones.

I've always used standard Aquabatten sections.