A simple strap with low-friction rings can improve mainsail performance.
Issue 148: Jan/Feb 2023
Sails are amazing fabrications. They start out as bits of flat cloth, and through the tailoring of the sailmaker and expert trim of the sailor, are transformed into effective airfoils. Of course, it takes quite a few adjustments to get it just right, and invariably the boatbuilder misses a few tweaks, leaving it to us as sailors to figure out how to tug the cloth in just the right way. That is sailing.
Several images showing the distortions that often occur without proper aft tensioning.
A common problem is keeping the luff near the tack or reef grommet close to the mast. Unless the grommet is firmly secured, the outhaul can break slugs or pull the bolt rope right out of the mast groove. Unfortunately, this tack attachment point is often a few inches too far aft to do the job properly. The sail is pulled outward for the distance between the foot and the first grommet, resulting in a crease running from the clew up to the first slide holding the sail into the mast track. When the sail is reefed the problem is double, since many boats with single-line reefing rely on the forward reef line to secure the tack, and it is even farther aft.
The dog bone pulls the tack back close to the mast, where it belongs. Even with the shortest shackle, the tack anchor point is about one inch farther aft than it should be.
The solution on many racing boats is a tack strap. Most often it is a Velcro strap woven through the tack ring and wrapped around the mast. Occasionally, it is a sewn part of the sail. On the J/70 tack strap, this works when the Cunningham is eased, but as soon as the tension comes on, the angle is not quite right. And the reefing horns on some boats are too far aft to carry the outhaul load. The Cunningham (aka downhaul) tension should be directed both forward and downward, but it’s seldom rigged this way.
The dog bone, just two low-friction rings sewn into a strap. The length is adjusted so that the
rings reach about halfway around the mast. Ball-bearing blocks will also work. The motion can scratch the mast finish; we later protected it with anti-chafe tape.
The solution is a simple dog bone sewn from webbing and two low-friction rings. Wrapped around the front of the mast, it redirects the Cunningham force in the proper direction. The Cunningham comes up one side, through one of the low-friction rings, through the tack grommet or reefing grommet, through the other low-friction ring, and down to the tensioning tackle.
The strap is best made from polyester or Spectra webbing, since these ride well on the mast, though it could be spliced from Dyneema single braid. You will need something to prevent the strap from sliding downward. An existing pad-eye or cleat will do. In my case, the handle for the roller furling boom is convenient. If the available fitting is too high, consider extending it downward with a pendant.
J/70 tack strap. And yet oddly, it is really in the wrong place. Or rather, another strap is needed by the Cunningham.
“But I don’t use a Cunningham.” Many boats tension the mainsail entirely by the main halyard. Give some thought to where your grommets are anchored. Look at the set. Perhaps a strategically placed strap or lashing will do the trick.
“When I reef, the tackline pull comes from the boom, actually pulling the grommet aft!” This is a common problem with in-boom single-line reefing. My last boat did that. I kept a length of line at the mast specifically for making a lashing around the mast to hold the new tack forward. Later, I positioned a pair of open blocks on the mast that I could place the tackline around, just like the dog bone, redirecting the pull forward.
The reefing lines need to pull outward at both ends, though I very seldom see it rigged this way.
On my trimaran, I like the dog bone, because it allows me to move the low-friction rings up and down as required. Because it has around-theboom roller furling, and we must lock the handle at whole revolutions, the reef grommet can move quite a bit vertically. The possibilities are limited only by the imagination.
The result is a sail that can be trimmed to perfection, with just the right tension angle at the tack and with the luff close enough to the mast to satisfy the most particular sail trim maven.
Good Old Boat Technical Editor Drew Frye draws on his training as a chemical engineer and pastimes of climbing and sailing to solve boat problems. He cruises Chesapeake Bay and the mid- Atlantic coast in his Corsair F-24 trimaran, Fast and Furry-ous, using its shoal draft to venture into less-explored waters. He is most recently author of Rigging Modern Anchors (2018, Seaworthy Publications).
Thank you to Sailrite Enterprises, Inc., for providing free access to back issues of Good Old Boat through intellectual property rights. Sailrite.com
