The Fully Battened Main

by Andrew Dove/Cruising Editor Nancy Knudsen on 21 Jan 2008 On our Peterson 46 Blackwattle, we have carried our fully battened main all the way round the world with great success. The combination of a fully battened main and batcars made it easier to reef as it reduced the friction, and the sail maintained its shape always without problems. After this troublefree experience, we would have a fully battened main as a high priority in any future enterprise.

So I found what Andrew Dove (Area Manager of Northsails in the Caribbean) has to say extremely interesting:

The first full batten main of any size that really impressed me was when I first moved from Montserrat to Guadeloupe and witnessed Philippe Poupons arrival in his trimaran Fleury Michon. The sail had an important roach and had adjustable batten fittings on the leech and luff receptacles. In France at this time there was an explosion in the multi hull market. One of the first suppliers of specific batten fittings was a small independent company called SDA. The owner was called Mr Patin. Non-French readers will miss an amusing detail here in that Patin means slider, an apt name.

The SDA system was always based on round battens that gave good stiffness in proportion to their weight. As a sail maker, shipping these battens was and still is a major problem. The system would fit the later ball bearing tracks or sliders and existed with long sliders that work remarkably well as their length avoids twisting which so often is the cause of the sail being difficult to hoist or lower.

Today most hardware suppliers have their system. Most modern day systems work well. They are specified for certain boat ranges and generally I think that the boat sizes given are accurate. To catalogue the problems seen on customer’s boats would be long but here are the main ones that come to mind:

Cars used have inadequate bearings for the compression. Obviously the greater the roach, the more the compression though more expensive. Buy cars with aluminium ends rather than plastic ones. Use torlon balls rather than a lighter polyester and on the head car at least think of using rods that spread the load.

Batten fittings vary greatly in price. Do not undersize these either, as some battens can pop out in gybes. This tends to happen when the batten passes from the intrados to the extrados of the sail where the distance around the curve is slightly longer. Battens should not be too close to reefs either, as horizontal reef line tension can pop the batten as well. Pocket size is critical here. The pockets should either have added volume proportional to the batten size, in which case should be flip flopped, one to port the next to starboard etc to balance the sail. A flat pocket should be large to envelope the batten without forcing against it. If large the leech end of the pocket with a tie in system must be tapered or equipped with a means to keep the batten tip central. A number of our 3DL mains have internally moulded pockets within the lamination and nothing is added to one side. These are lighter and smoother and adapt well to the C Tech or Antal type fittings that sit within the pocket.

In the Caribbean many systems have corrosion problems. Obviously a sail with any carbon content should avoid metals, other than titanium, or must take great care in insolating the metal from the fitting. Plastic type end fittings can wear early where aluminium or stainless screws attach the sail to the luff cars. The thread in a plastic type fitting is always fairly fragile.
The aluminium leech screws can oxidise rapidly in a tropical environment, one needs to control such fittings from time to time.

The batten’s role is to support the sail’s leech. Battens do not shape a sail as much as allow the design shape to be expressed. On a small roached mainsail, batten compression is limited and batten diameters and materials less critical. However, as roach size increases the need to resist compression is greater. Carbon battens obviously give the best stiffness for a given weight. Early carbon battens were very brittle and would break in a poorly-controlled gybe. Batten construction is now better and a Kevlar covering is often used to make carbon battens very long lasting. Polyester battens often become soft at the maximum draft position on the sail. A useful tip for non tapered battens is to invert the battens each time the sail is removed from the rig for servicing.

When designing the sail, care should be taken that the batten does not full at the same height as the spreaders. With swept back spreaders the spreader tip can push on the middle of the batten and invert it. The extra wear of the batten against the spreader should simply be avoided.

Sail draft in a soft Dacron main can wear the battens as the batten needs to change shape completely from tack to tack. Even on flat windward sails, as the enormously roached Class America sails, a crew member is needed to kick the battens in the lighter airs. On a high roached Dacron main stiff battens can help roach inversion though the cause of this problem is the clothes resistance to load. To maintain leech tension Dacron sails need to be deeper than a higher modulus solution. Using a Fan cut Dacron layout where the panels remain perpendicular to the leech helps to maintain the leech loads along the thread line of the sail cloth limiting stretch. On heavily cambered mains the battens may stay backed in light airs. Certainly if you have a rigid vang, then slacking temporarily the halyard, then retensioning it immediately after the tack or gybe, will avoid you needing to apply AC techniques.

One can apply vertical tension to the sail through mainsheet tension but most importantly though halyard tension. Many full batten mains need an enormous luff tension. Anybody who has sailed a beech cat will realise the downhaul tension applied to establish the sail. I have been involved in the Ponnant 90m sailing ship project that has full batten mains. Initially the boat was regularly breaking the 36mm Spectra halyards. This was ten years ago and I’m certain that halyard technology has evolved. However we plotted hydraulic pressure against luff tension measured by a Newton metre inserted in the base of the luff. When I got the market to rebuild the mains we set the batten ends along the normal luff curve but cut negative curves along the luff between the batten points. This way we were able to reduce halyard tension by basically a third. The boat stopped breaking its halyards. This boat was not too concerned by compression in the mast but obviously this was greatly reduced by the same occasion. The most recent sails for this boat have added an adjustable luff line as one would find in an asymmetric spinnaker or code O which would seem a good idea.

Battens though necessary are often heavy. In the battle to reduce weight to avoid pitching and healing the number of battens should be reduced to a minimum. Often intermediate floating battens are sufficient. I often prefer to have the lower battens long but not full-length. This eases handling when reefing. As a rule the most compression occurs where the change in roach angle is maximum. The new Americas Cups mains are amongst the sails with the biggest roaches. These have a number of battens grouped in the head to support the compression loads here.

Boats of all sizes have in boom furling mains. This choice is motivated by their theoretical ease of handling. These allow push button sail control without adding much weight aloft. The sails have to be fairly flat and be built such that the cloth weight is evenly distributed on the luff and leech so that the sail furls around the mandrill fairly. If the sail has any real roach then batten pock is a problem. It can cause premature bolt rope wear and bunching behind the mast when furling. I personally prefer 95% length battens stopping within a reinforced area just behi