A Rational Discussion of Full Length Battens

This article will consider, in some detail, the subject of full-length battens. Out of necessity, there will be digressions into other batten lengths, and the characteristics of the sailboat and the mast the sail is set upon. We will look at how the battens affect the shape of the sail itself, in light air, moderate air and heavy air. We will look at what happens to the battens on a run. What about raising and lowering the sail? What are the sail design considerations which come to the fore...what about "lots of roach?" There is a whole container load of often unconsidered baggage that comes with what batten length you choose for your sail. Some of it is good, and some is not so good.

So what do battens do anyway? This seems like a good question to answer right in the beginning. I see battens as having two primary jobs: (1) they allow us to add roach to the back edge of the sail, and (2) they act as a stress reliever, or a load sharing device for the yarns in the sailcloth which makes up the leech of sails. The stress reliever aspect is the result of the battens forcing the leech of the sail into a relatively flat surface, allowing all the yarns which pass under the batten to share the mainsheet load, thereby reducing the load on the yarns in close proximity to the leech, and thereby reducing stretch.

A long time ago, people who were making sails found out that if an edge of a sail was not supported by some type of spar, like a mast or yard, it had to have a hollow cut into that edge to prevent it from flapping in the breeze. But sailors have also always been looking for "a little more area..." Some bright person found that by adding skinny little sticks, which lived in pockets on the sail and were placed roughly perpendicular to the edge, they could begin to cantilever sailcloth out past the straight line defining the edge of the sail. The sail was getting bigger!

If we roll time forward to when people were trying to handicap sailboat performance for racing by measuring the hull and the rig, it should be no surprise that batten lengths were of interest to the rule makers. It had been understood for a long time that longer battens allowed sailmakers to build mainsails (or jibs for that matter) with wider girths. The original attempt to limit girths was done via limiting the batten length. A sailmaker could make a mainsail as wide as she liked, but with the short battens of CCA and early IOR rules, the leech would fall off to leeward, yielding a slower sail. There have been some highly imaginative attacks on the mainsail midgirth problem. One of my favorites was the mast with a huge permanent bend way up near the top. This effectively moved the headboard way aft from its "normal" position, allowing/requiring the sailmaker to put in a huge amount of "roach" (actually luff round) in the luff edge of the sail instead of the "normal" roach on the leech edge. In this way the sail ended up with a massive midgirth, even though it still used short battens. The obvious solution to the midgirth problem is simply to measure the girth on the sail itself, which is what the rule makers eventually decided to do. What went wrong was that they did not go back and reassess the batten lengths, which were left unchanged from the earlier rule.

So along comes SCORA, the Southern California Ocean Racing Association. They were asking themselves "Now that the size of the mainsail is strictly limited, what can be done to make the sail last longer?" Why is it that after a year or so the sail develops a deep crease, or "V" at the front of the top batten? And a few years after that, the crease runs down past the front edge of all the battens? It looks ugly, and certainly goes slow. A bad combination. So these SCORA folks started messing around with batten lengths. Part of their study involved retrofitting longer battens onto old, tired mainsails. They found that the back edge of the sail showed a huge improvement in shape. Basically, the number of yarns which had previously done all the work grew by the percentage increase in the length of the battens. At the location of the number 3 batten (counting down from the top), the SCORA length is double the old CCA/IOR length, so each yarn is doing half the work it did before! Simply fitting the longer battens into an old, tired sail removed the crease, flattened the leech, and moved the draft forward: an altogether healthy combination.

IMS eventually was forced to lengthen their batten limits also, although regrettably they refused to simply adopt the SCORA lengths, but instead came up with their own maximums, slightly shorter than SCORA. And they still kept their huge rating penalty for battens longer than the maximums. They have trouble with the notion that batten length is not a speed producing factor. Speed comes from two things: sail shape and sail size. They have a good handle on controlling the size. Batten length does not really improve the shape of a brand new sail, it just keeps an older sail looking new longer. This is not something to penalize.

The idea of full-length battens is certainly not new. If you have ever seen a picture of a Chinese junk, you know full-length battens have been around for thousands of years. However, the application of full-length battens to modern displacement boats with sloop rigs is relative new, at least in large volume. The remainder of the article will discuss the pluses and minuses of full-length battens versus sails without full-length battens.

There is a whole collection of boats which have gravitated towards full length battens for good reason. ("Good reason" in this case means substantial improvement in sailing performance.) As a group, these tend to be high speed sailing craft like sailboards, multihulls, Aussie 18's, the America's Cup Class boats, and the like. What these boats have in common is they tend to sail at relatively small apparent wind angles, especially when on a run, compared to a conventional sloop. This stems from the fact that this group sails runs going so fast that they pull the apparent wind angle way forward. A byproduct of boats which sail runs at small apparent wind angles is that their optimum sail shapes are flatter.

A good (and extreme) example of a high speed sail boat is the 60' trimaran "Lakota" owned by Steve Fawcett. "Lakota" sails on a run so fast (20 to 25 knots of boat speed is common), the apparent wind is always well ahead of the beam, usually hovering in the 50 to 60 degree range! There is really no circumstance when a spinnaker has any value. Their fullest sail is a roller furling jib top which is set on a bow pole to hold it further out in front of the boat. Their mainsail is not substantially fuller when they are running than when they are beating, because the apparent wind angle is not all that different.

Compare "Lakota" to a conventional displacement sloop, like a Cal 39, which sails downwind at boat speeds like 6 to 10 knots. The Cal will be sailing at apparent wind angles of 150 to 165 degrees. Full sail shapes are required to generate power while sailing at these large apparent wind angles. The Cal 39 will need a much fuller mainsail shape for sailing runs than "Lakota."

Let's look at how a mainsail behaves when full-length battens are used and when non-full-length battens are used.

In the case of a non-bendy mast (which is most cruising boats and a large percentage of production boats), full length battens take control of sail shape, essentially over-ruling the effect of changes in the outhaul and the cunningham. The sail can be made flatter by (a) using stiffer battens or (b) reducing the tension on the battens themselves. The sail can be made fuller by (a) using more flexible battens or (b) increasing the tension on the battens. An extrapolation of this is that the sail shape is basically predetermined by the batten stiffness. This means the shape will be "okay" almost no matter what you do or don't do to trim it.

In the case of a flexible mast, mainsail shape can be adjusted by bending the mast. The sail becomes flatter when the middle of the mast is bowed forward compared to the head and tack. In this case, full-length battens do not overwhelm the shaping of the sail.

It should be pointed out that many of the 'high speed sailing craft' mentioned above have yet another method of shape control by having a selection of sails, and even rigs(!) to choose from. The sailboard people have "quivers" of sails and masts, as do the Aussie 18's, with rigs numbered 1 through 4. It may be that the America's Cup has nothing to do with most day to day sailing, but the wind range of their mainsails is only about three to four knots wide! More or less wind by that much makes them wish they were using a different mainsail.

It is surprising how much the full-length battens control the sail shape. Easing the outhaul to try to fill out the sail for running will affect the sail mostly up to the bottom batten, and produce very little change above the batten. Changes in the cunningham seem to have less effect on the draft position, but this might be due to friction between the sail slides at the front of the battens and the sail track. If the change in the cloth tension induced by the cunningham cannot distribute itself the whole way up the sail, then the draft position will not be affected.

One occurrence where full length battens have a distinct advantage is when motor-sailing. The mainsail will generally sit quietly on one tack or the other if you are motoring around with the sail up.

Full-length battens can pose a difficulty when sailing in very light air because the battens seem to be more comfortable/stable when the mainsail is sitting on the wrong tack! The fixes which seem to help minimize this behavior are less halyard tension and less batten tension.

One concern I have with full-length battens is when the boat is overpowered. Suppose you are beating with a genoa and a main which does not have full length battens. Suppose the wind has recently filled in to the point where you wish you were sailing with a #3 jib instead of the #1 genoa, but you're stuck with keeping the genoa up. You can control angle of heel by making the mainsail as flat as you can (lots of outhaul) and lowering the traveler (so you are getting drive only off the leech of the mainsail), and as much back stay as you dare to straighten the forestay and therefore flatten the genoa. At this time the front of the main will have a large bubble in it, caused by the large volume of air exiting off the leech of the genoa. This is known as backwinding the mainsail. It may look awkward, but it is the fastest arrangement given the constraints. If we look at this same circumstance using a full batten main, the battens will prevent the bubble from forming in the luff, essentially forcing the mainsail down into the high speed exhaust flowing off the jib. This is now constricting the air flow, essentially acting like an air dam, preventing the air from exhausting off the leech of the jib. This will be a performance liability...but it will "look better."

When sailing a run with a conventional displacement boat, and the boom is out at 90 degrees, full length battens suffer from some extreme bending around the leeward upper shroud. The wind is pushing the batten (the whole sail) to leeward outboard of the shroud. The batten is constrained to lay against the shroud, and also be connected to the aft edge of the mast. This contorts the batten into an 'S' shape, and can causes failures at the front end of the batten pocket if the batten cars are not strong enough.

When running, there is the problem of chafe between the shroud and the mainsail. Certainly when you rub sailcloth against a stainless steel shroud, or a spreader tip, the sail will give way. Full length battens tend to cause the sail to chafe faster because the sail cloth is pinched between the shroud and a fiberglass batten. I'm not sure how important this problem is, however. I don't think holes of this type are threatening to the life of the mainsail, unless you are sailing around the world or something similar. What can be done to mitigate this? Placing chafe patches where the batten pockets contact the shrouds will be about the only thing you can do. But let's talk about chafe for a minute. Chafe does not happen when two items touch each other. Chafe only happens when two items rub against each other. There must be movement for there to be chafe. The movement that is the problem here is caused when a gust of wind hits the mainsail. The leech is blown to leeward, causing the boom to rise. As the boom rises, the sail is sliding up across the shroud. After the gust, the pressure on the leech is reduced, allowing the boom to drop back down again, so the sail slides down the shroud back to where it was before. Every time there is a change in apparent wind strength, this movement occurs. If you can reduce the movement of the sail against the shroud, you will get less chafe. This can be accomplished by using a boom vang when sailing downwind. The primary purpose of the boom vang is to control the shape of the leech of the main when sailing on a reach and a run, and it will inhibit the up and down movement of the boom. You will have less chafe and more control using a boom vang no matter what batten length your mainsail has.

I have covered most of the sailing behavior of full length battens. I would like to now address the sail handling differences between full-length and non-full-length battens. These are mechanical things which are different when using full-length battens as opposed to non-full-length battens.

The most alarming difference comes from what I call batten droop or batten thrust. When raising (or lowering) a full-length battened mainsail, the leech end of the battens tend to be lower than the front end. This batten droop causes the batten to thrust the luff slide (or sail slide) at the front end of the batten against the mast track. Note that if the batten did not reach the luff slide (not full-length), then, even though the batten droop is still there, it has no effect on the slide. In general, luff slide tracks are designed to be pulled away from the mast, because, without full-length battens, that is what the mainsail does. The change to full length battens completely reverses what is going on. The battens are now pushing the slide towards the mast. There will be a great deal more friction when trying to raise or lower a fully-battened main than a non-fully-battened main. The solution to this problem is to buy specially designed luff slides which are intended to deal with the compression loads from the battens. On boats over about 30 feet, often times the solution is to replace the sail track on the mast with one which is designed to deal with both tension and compression loads, and has low friction slides (now called 'cars') which make raising and lowering the sail much easier. This solution will easily run into the thousands of dollars for sail track and cars only...sail not included!

Nearly all sailboat hardware companies have products aimed at solving this problem. And, no, the products are not all the same. Ronstan, Harken and others offer ball bearing cars. There have been reports that the balls can get gummed up, especially if your boat spends some time in a boat yard where there is sanding and painting going on. In this case be sure to clean the cars carefully after leaving the yard. Antal offers a sleeve type car which fits snugly around their track and requires almost no maintenance. Tides Marine has a product called Strong Sail Track and Slides (suitable for mainsails up to 450 square feet) which uses brass slides on a plastic track. The ball bearing cars like Harken and Ronstan are quite tall. Harken's smallest batten traveler system, "System A", uses "bat-cars" which are 3 inches tall. The headboard carriage is 7 7/8 inches tall. The intermediate cars are 2 1/8 inches tall. (Conventional sail slides average around one inch in height.) A by-product of this is that when the sail is stowed, it will stack much higher on the boom than with conventional sail slides. Putting the main halyard onto the headboard will require a longer reach than before. Note that when the sail is reefed the reef tack position will be higher above the boom because of the height of the sail slide cars. Starting the sail slide track as close to the gooseneck as possible will help.

Full length battens also carry a weight premium. They certainly weigh more than the battens in a conventionally battened sail. And when you add in the weight of a low friction batten carriage system and it's track, it can be easily double what a conventional mainsail would weigh. If all other things are equal, less weight aloft is better than more weight aloft.

We often hear that full length battens and lazy jacks have some sort of connection with each other, as if lazy jacks won't work unless the sail has full length battens. Actually lazy jacks or the "Dutchman System" work equally well independent of batten length. In fact they will all work with no battens at all!

What about sail design considerations made possible by full-length battens?

The most common request relevant to full length battens is for a sail with "lots of roach." There have been plenty of misleading articles on this subject. First of all, most boats have a standing backstay, and the back stay serves as a pretty good limiter for how much roach can go into a sail. For most boat owners, having to lower the main halyard in order to tack or gybe is pretty much out of the question. In a large percentage of all boats, a sailmaker can get the roach to reach the back stay using non-full length battens, so don't think you need full length battens in order to have "lots of roach."

Now of course if you DON'T have a standing back stay, then things are much different! If you consider the fluid dynamics of sail design, what we as sailmakers would like to get away from is sails with pointed heads. "Lots of roach" is very good, especially if it is near the head of the sail. (Note that we no longer see rudders or keels with pointed tips.) But when we look at boats with no standing backstay, we have just switched over to "high speed sailing craft like sailboards, multihulls, Aussie 18's, the America's Cup Class boats, and the like" as mentioned near the beginning of this article. And, as a group, that collection of boats have trailing edge shapes which are very attractive from a fluid dynamics point of view, and very fast as I mentioned before. There is also a collection of boats with free standing masts, like the Nonsuch line, some of the Freedoms, and the WyileCat 30's, where, if the sailmaker is not constrained by some rule (like PHRF), the roach can become quite large. In these cases full-length battens are the only way to support the large roach, and work very well.

Probably the fastest way to wear out a mainsail is to flog it to death. Mainsails tend to flog when sailing overpowered with the jib exhaust dumping onto the mainsail. The sail tends to flog more if there are concentrations of unsupported weight on the leech, as in reef clew patches. Each reef clew patch is composed of 6 to 10 layers of sail cloth which are the reinforcement for the reef clew ring. Then there is the reef clew ring itself, and if the boat is over 35 feet, there might be webbing to anchor the ring to the patch. Then there is the leech line cleat and its cover. This adds up to a lot of weight, and is a 'catalyst' for flogging. One of the features of full length battens we like to take advantage of is their ability to stabilize the reef clew patch. If we can design the mainsail so there is a batten which runs right across the reef clew patch, the batten will do a good job of reducing flogging because it will help hold the reef clew still. To accomplish this properly, the number of reefs must be predetermined, and the number of battens and their locations must be allowed to float to the location which does the most good. Usually either five or six battens will work nicely, depending on how many reefs the sail will have.

You may now know more than you ever wanted to know about batten lengths. We make mainsails of both varieties. Both styles of battens, batten pockets, and associated hardware are carefully developed to be the strongest and most reliable. But we want to be sure that you evaluate the marketing efforts which have somehow convinced many people that a mainsail with full-length battens is somehow easier to handle. Consider that "bat-cars" never existed before the full-length batten mains became common...which I interpret to mean the fancy cars were not needed in order to raise and lower a sail with conventional battens. (It is hard to imagine how easy it would be to raise and lower a mainsail with conventional battens and ball-bearing luff sliders!)

There are pros and cons to both batten styles. Hopefully with this knowledge, you can make a wiser choice when deciding what to do about batten lengths when ordering your new mainsail.


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