Changing sail shape with backstay adjustment

The adjustment of sails is based not only on the tension to be given to the sheet, but also and especially by changing the shape of the mainsail and jib through various maneuvers: the halyards ,the base, the barbers or the trolleys to mention a few examples. One of the quintessential adjustments that goes into the shape of sails is the tension of the backstay, or forestay.

Paterazzo, how it evolved

It used to be just a fixed forestay, then “evolved” into maneuvering with the first tension adjustment systems that were later well developed during the 1970s-80s. Today the backstay sometimes reverts to fixed, non-adjustable, on some models of pure cruising sailboats, such as those for charter, but it has not stopped evolving in its version from “maneuver”, with the introduction of a material such as the textile That greatly improved its performance.

Until about 20 years ago the most popular backstay material in fact was steel, today textile materials have almost totally replaced the old solution offering the same or better performance in cable tenacity, along with significant weight savings.

Backstay, what it’s for

The main function of adjusting the backstay is to change the shape of the sails, both jib/genoa and mainsail, by smoothing them out. When we cock the backstay, the masthead goes backward, thus stretching the forestay, especially in masthead rigs, while the middle area flexes going forward. The curvature of the mast causes the mainsail and jib fat to shift toward the bow. The sails are thinner, and the two effects combined cause the boat to swerve less and be less eared.

Conversely, when we leave it we give power to the sails: the forestay increases su catenary and the jib has a deeper shape, the mast straightens and the mainsail fat increases moving aft. In very light wind conditions upwind, 4-5 knots, the backstay should only be pinned (in the case of masts with in-line spreaders) or even, in masts with quartered spreaders, practically banned.

In the stern, if the mast has spreaders in line, the backstay will have to be held with a minimum of tension at all times, and totally capped in high winds. In angled spreader weapons, the shrouds already support a good portion of the mast load, and a different adjustment can be dared, leaving it altogether with little wind and holding it at moderate tension with a stiff wind.

Mauro Giuffrè