Durability of Sail Material
Source: Steve Haarstick
How long will my new sail last? I probably hear this question more often than any other, yet it’s one that is very hard to answer. Now that the start of the sailing season is finally at hand, it is a good time to look at the variables that affect the life of your new sail.
The most important variable in the useable life of your sail is your tolerance for changes in the sail’s shape with use. The stretch properties of all sailcloth will change with use. The more severe the use, the poorer quality of the cloth, the greater the change, and the faster it occurs. Different types of cloth will show different shape changes. But more important than all of these factors is your individual tolerance for the shape changes that are unavoidable.
For example, if you are a world class sailor preparing for the Olympics, any shape change from “brand new” is unacceptable, and new sails are often discarded after one regatta. Durability is obviously not a concern at this extreme level. On the opposite end the spectrum, you may consider that your sail is still “good” as long as it remains in one piece. In this case, shape change and loss of speed potential is not as important. These two sails could have the same cloth, and be used in the same conditions, but the second example will be considered useable for a much longer time.
Your sail’s lifespan also depends on how you use it: Most important is the average and maximum velocity of the wind in which the sail is used. The damage that heavy air inflicts on a sail derives from two sources: The first, and most damaging, is flogging in heavy air. The energy that is available to destroy your sail is proportional to the square of the apparent wind. That means that in 25 knots there is four times the destructive force than in 12.5 knots apparent.
To minimize damage to your new sail, there are just a few rules that you should follow: Do not practice reefing or tacking in heavy air with your new sails, use your old sails. Avoid flogging your sails whenever possible by minimizing unnecessary tacks or gybes before the start of a heavy air race. Never hang your sail from the rigging to dry in a breeze! Don’t walk or sleep on your new sails. Don’t stuff them in the bag. Instead, roll or flake them. Don’t bake them in the trunk of your car. Take the time to tape over sharp edges everywhere: spreader tips, mast and boom fittings, cotter pins, lifelines, spinnaker pole, anything that can snag or tear your sails. Make sure your new genoa has the spreader patches in the correct location: 99% of tears can be avoided with a careful eye. There is no cloth that is immune to tearing. Not Kevlar, Carbon, Pentex, Spectra, Dacron, and especially Nylon. There is no quicker way to demo a new sail than a major tear!
The second source of sail destruction in heavy air is the greater chance of overloading the cloth beyond its elastic limit, particularly in the high load areas of the sail. This becomes more likely as the sailcloth ages. All cloth looses strength with use. Some types of fabrics loose strength much faster than others. A durable sail must retain enough strength after extended use to avoid overloading and the permanent damage this causes. Laminate sails are especially vulnerable to delamination at the inside edges of the corner reinforcements. This can be an acute problem with the “string” constructions popular with other lofts.
Before you consider purchasing the lightest possible sail, keep this thought in mind. Sails that are built as light as possible, also have the smallest safety margin. When the sail material looses strength with use, the possibility of overloading becomes more likely. If this loss were just a little, safety margins could also be small. However, many fabrics loose a high percentage of their original strength with use. It is critical to know how much loss occurs if there is any chance of predicting the structural life of your sail. Without testing the cloth, in particular, without our Impact Flutter testing, you can’t know how much loss to expect. Without taking these losses into account, it is very easy to pick a fabric, or construction that will not have the necessary residual strength to carry the stresses without excessive, permanent distortion. It is not unusual to see Kevlar laminates loose over 50% of their original strength over a reasonably short period of time. Add in Kevlar’s extreme losses in flexibility and strength due to U.V. exposure, can reduce it’s residual strength even further. Other laminates made with substrates made from fibers such as Technora, and Carbon are much less sensitive to U.V. exposure. The more recent Flex Technora laminates from Dimension may not be as strong as Kevlar initially, but loose much less strength with use. Trading off a little more stretch when new, for less change of shape with use is also a valid choice when durability is concerned. We have substituted these new Flex laminates for many Pentex, Kevlar, and even Carbon sails for boats 40 feet and under with excellent durability.
We have also had excellent results with the Carbon materials that we have used for the past 10 seasons. Carbon laminates are not the brittle, super high modulus Carbon used in the American’s Cup sails. They are much more tolerant of fatigue and flexing, and they have NO U.V. loss. Carbon fabric looses far less of its original strength with use than any other laminate we have tested.
And, we HAVE tested sailcloth since the late SIXTIES (over 40 years!)! There is no doubt that our testing is critical to predicting the long term performance and durability of your sails!