Battens are an important part of the sail structure, but with many different options and different use cases, it can get confusing. Here is the lowdown on battens and what you need to know to choose the right ones for your sailing needs.
Battens are the primary structure of a mainsail. They support the sail's shape, improve overall durability by limiting the effects of flogging on fabric, and remove any limitation on size (roach area). Full-length battens in the top sections of the sail are now common.
Traditionally, mainsails designed for serious offshore work limit the size of the roach (area outside the straight line between clew and head), reducing the need for battens in an attempt to maximize durability and reduce maintenance. Hardcore blue-water cruisers sometimes go so far as recommending the elimination of battens entirely. They argue that battens and batten pockets are maintenance headaches and sources of potential failure. Removing the battens, however, has a huge impact on the shape, life, and size of the sail, and performance is affected dramatically.
Before you decide to add or remove your battens, it’s important to fully understand their role.
What Battens Do
Battens are like the framework of a tent across which the material is pulled taut and smooth. They support the area outside the straight line between clew and head. Without battens, this area would flap uncontrollably. Full-length battens, if they are stiff enough at the back end and tapered toward the front, also help maintain shape.
Acting as “I” beams, they resist the forces on the sail that try to compress the leech in towards the luff when the sail is sheeted in. This preserves the open leeched airfoil shape and keeps the sail from becoming fuller and more semicircular (rounded leech) as the breeze and the loads increase. A flatter airfoil shape with a straight, open leech keeps the boat upright and reduces weather helm. The more roach you need to support, the greater the compression, and the more important battens become.
A batten running the entire width of the sail is most critical in the top sections of a mainsail because the roach represents the greatest percentage of the cord (straight line distance between leech and luff). In the lower sections of the sail, the roach is a smaller percentage of the cord, so the battens don't have as much work to do.
Full-length battens carry the compression loads all the way to the mast. If the battens are shorter, the loads are transferred to the material of the sail wherever they end. Over time, the fabric breaks down and hinging develops.
The bottom line is that the more full-length battens, or framework, are used, the more durable the sail will be, and the better it will hold its shape in a breeze. More structure equals less flog and quieter luffing (as when taking a reef). Reduced flogging will preserve the resination that holds woven materials together and makes them stretch resistant.
At a minimum, full-length battens should be used in the top sections of the mainsail.
The Downsides of Full Length Battens
The downside to full-length battens is the compression they transfer to the luff hardware. The battens force the luff of the sail into the back of the mast. The sail slides that attach the sail to the mast are loaded up, creating friction, and causing them to twist and toggle in the groove. In worst-case scenarios, slides can become locked up and prevent the sail from being raised and lowered (making it only possible to raise or lower if the boat is perfectly head to wind).
Offshore, this creates a problem when trying to reef or drop the mainsail completely when reaching and running. At a minimum, batten compression causes chafe and wear at the inboard end where the batten presses against the mast. When eased to sail off the wind, the battens will want to poke past the mast, creating a V-shaped wrinkle. Each of these problems is magnified as the sail gets bigger.
The keys to all of these issues are the batten receptacle and the type of slide used. Batten receptacles are the boxes that contain the batten on the luff end and connect the sail to the mast. They eliminate chafe and wear. Ideally they have a stainless steel, articulating universal joint to keep the batten from pushing forward while allowing the batten to spin independently of the slide.
The type of slide used has an impact on how well the sail goes up and down. Flat slides (the most common type on newer boats) are best. They cannot get twisted out of line. Round slugs are the worst because the twisting forces will often cause them to lock up in the groove, particularly if they are smaller in diameter. External claw-type bronze or nickel-plated steel slides (found on older masts) are a problem too, due to the inherent friction of the claw arrangement, and the joints between the sections of track. On larger sails, a separate, external luff track (like Tides Marine, Antal, Harken, etc.) becomes necessary to insure easy operation.
If some or all full-length battens are used, you must decide how to attach the sail to the mast. Make sure to consider the headboard, which is often the chief source of difficulty. Over the past twenty years, a number of alternatives have been developed. While none is perfect for every application, with a little planning you can choose the method that does the job and fits the budget.