A Sail Replacement Strategy

How do you know when a sail is past it's prime? The camera never lies. "Sail Tech" from our November/December 2009 issue.

It’s the time of year when most of us look back on the season past to remember the good times, attempt to forget the bad, and also think about how to improve next year. A big step toward this goal is taking a hard look at the sail inventory and evaluating what’s good, what’s bad, and what’s ugly, yet maybe usable for another season. Te main reason it’s appropriate to do this now rather than during the spring rush is twofold: sailmakers offer significant fall discounts, and your memories of these sails are fresh from just having used them.

But what criteria do you use to separate the inventory into these three broad categories?

First, have a critical look at each sail and evaluate what Will Keyworth at North Sails Chesapeake calls its “functional condition” and then it “performance condition.”

“By functional I mean its physical shape,” says Keyworth. “If it’s been patched heavily, been repaired several times, or has delaminations in the cloth, then it may be beyond repair or re-cutting and should be replaced. Then, even if you use it for a non-serious regatta and it blows up, you have a replacement ready.”

If the sail passes this first test, then it’s on to the test where “performance condition” means something much more subtle: how the sail hold its flying shape relative to what it was designed to do when new.

“Just like people, sails will start to change shape with age,” says Keyworth, “so we want to look at how a sail has been able to hold its designed depth and draft position in its range of windspeed. As the material shrinks or starts to breakdown and stretch, the shapes tend to migrate toward being flat-forward and draf-aft.” This less-than-ideal shape creates more drag than lift.

Critiquing sail shape is now easy using photographs of a main or jib. Sailmakers use sofware that can analyze the shape of the sail, usually along the middle and upper draft stripes, to measure depth and draft position. North Sails’ Dave Scott uses such a tool, called Sail Scan, and an example of a J/109 sail analysis is shown below, which depicts all the relevant dimensions of the sail’s flying shape in the existing conditions of wind speed, angle, and rig tune.

John Baxter, of Doyle Midwest in Chicago, says these software tools are best used with customers to show how the shape evolves from when new—an example is shown belowfor the genoa on a new and a three-year-old Beneteau 36.7, which got a lot of heavy use throughout the season as the only class-legal sail.

“This sail was used for every race, Wednesday nights, and practice over that time,” says Baxter. “It probably has more than 500 hours on it, and was the only genoa the boat had.”

Part of determining when and what to replace will depend on a boat’s particular budget and its needs. “The genoa and other upwind headsails are the most abused sails of a boat’s inventory,” says Baxter. “They are flogged, bashed into the mast, pushed out of their intended wind range, crunched up on the foredeck, stepped on, and sometimes even dropped overboard. This constant abuse inevitably leads to a change in sail shape. In the new era of membrane-type sails this shape change is sometimes not as noticeable [as Dacron sails] because the sails remain smooth.”

One element of laminate sails technology is the “shrinkage” problem, where the wrinkling of an otherwise smooth surface causes a reduction in the sail’s dimensions.

“A typical 40-foot light No. 1 genoa could shrink as much as 6 inches on the luff over the first two years,” says Baxter. “This is a problem of any film-type sail regardless as to what construction method is used. Typically, the lighter the sail the more likely it is to suffer from this shrinkage as the sail ages. In most cases some simple retuning will do a lot to keep the sails fast for longer.”

Given this, how does one decide to replace or try a re-cut?

It depends on the severity of deformation, but sometimes recuts can add a little more life to the sail. Keyworth says the typical re-cut is done by adding luff-curve and sometimes negatives
to the leech to help flatten the exit shape.

“At best, and only if the sail material is sound and not too damaged from sunlight, you can get a maximum of two re-cuts to a sail,” says Keyworth. “After that, you’re just wasting our time and your money.”

But while this shape may be OK for one more season, perhaps with a minor re-cut, there must be a point at which a sail has outlived its useful life and simply has to go. So, when should we replace?

“This is all determined on what is most important,” says Baxter. “In most cases, a boat will try and stay with some sort of normal sail rotation. For boats that have larger inventories, there are some sails that do not get much use, and others that do most of the work. Even though mainsails are up all the time, the abuse they get is usually far less than that of a genoa or spinnaker. This is a result of the sail being supported on two of its three sides, not hitting the mast, and not being flogged as much due to its having battens.”

The most commonly replaced sails, therefore, are the No. 1 genoa, half-ounce spinnaker, and then the mainsail. In most sailing venues, No. 3 jibs are not used as much, so they tend to retain their design shape longer. Baxter and Keyworth both say careful planning is a must, so when it does come time to replace the No. 3, an owner can slot it in.

And what about spinnakers? They’re harder to evaluate in shape, but much of the same principles apply, but perhaps even more so: due to their constant handling through sets, jibes, and drops, the melamine finish on the cloth, which is important for both strength and to limit porosity, starts to break down.

“In many cases spinnakers are probably the most overlooked sails in the inventory,” says Baxter, “and it is common to see boats out sailing with five-year-old spinnakers. The sails still look fine shape-wise, but they are porous. Because they are unsupported in how they fly, they load very differently than a mainsail or genoa. As the finish wears off, more air passes through the sail than is retained.”