This is a loaded question! The answer every cruising sailor wants to hear of course, is ‘forever.’ Or at least, ‘a very long time.’ In reality, the answer is more complicated. As a triangle, sails will last for a surprisingly long time. Structurally, though, sails gradually lose their integrity as the materials and stitching fail under the influence of the sun and use. The second part of the answer has to do with shape. Sails which stretch too much are unable to retain a critical airfoil shape (having a distinct rounded entry and flat, straight exit). This failure in shape costs you in subtle ways.
How long this degradation process takes is obviously influenced by how much sunlight and how strong the UV is to which your sails are exposed. Other factors that come into play include the amount of breeze in which they are used, how much flogging, chafe, and other abuse they receive. Ultimately, a better way to think of the structural life of your sails is in terms of hours of use. A reasonably well-treated woven polyester sail that is maintained regularly will last 3500-4000 hours.
A typical weekend cruising sailor using his boat two weekends/month, plus two weeks of cruising, over a five-month season will accumulate roughly 240 hours per year; these sails will last for 16 years! At the other extreme, a person living aboard their boat and cruising the Caribbean extensively will use their sails as much as 12 hours per day, 12 days per month, all year round, for a rough average of 1,728 hours a year. This sailor will be replacing sails every 2.5 years. Do the math for your type of sailing and you’ll get the idea.
The second part of the answer for life of sails has to do with its shape-life. This is more difficult to assess since sail shape deteriorates gradually with every hour of use and the effect of this on performance is much harder to judge than the physical condition of the cloth. Sails which stretch too much become too full and unable retain a critical airfoil shape (having a distinct rounded entry and flat, straight exit); this loss costs you in subtle ways.
At this point you are probably thinking, “I’m just a cruising sailor, I don’t care about performance.” Actually, cruisers do care about performance, it’s just based on different criteria. Cruisers, typically, are not on the quest for another tenth of a knot of boat speed or one degree of pointing. But sail shape is critical to control heel.
Full, stretchy sails, rob power in light air, but more critically, they create heel and weather helm just when we want control. At some point, we have to sail upwind – usually at the least convenient times. One of the real luxuries and pleasures of a good cruising boat is the ability to sail effectively upwind when necessary. If sails do not have proper shape, and the materials and structures are not designed well enough to resist stretch, the boat will not be able to go upwind effectively.
Unfortunately, shape-life degrades more rapidly than structural life. Sails will be triangles long after they cease resembling anything like a critical airfoil. Shape-life is very dependent on harshness of use, but even when treated well, sails can only be expected to retain good shape for only half to two-thirds of the structural life of a sail – that’s roughly 1,700 to 2,700 hours of use. How much deterioration in sail shape you are willing to accept is largely a subjective matter. Periodic recutting helps. As long as the material is in decent condition, excess shape can be removed and an effective airfoil shape restored.
Relative to much of the gear on your boat, sails do last a long time; but unfortunately, not forever. When you do decide to replace them, you will be pleasantly surprised. Your boat will come alive as dramatically as if you had put a new engine in your car. There will be spring in her step. When the wind is up there will be a greater sense of control, and going to weather might be fun again (at least for short periods of time).
To help protect your sail investment, here are some suggestions:
- Protect your sails from unnecessary exposure to sunlight and heat.
- Avoid prolonged luffing and flogging.
- Motor with your sails down unless they can be filled.
- Never back a genoa against the spreaders when tacking.
- Use the correct halyard tension. Halyard tension changes as a function of apparent wind velocity. Add just enough tension to remove horizontal wrinkles as the apparent wind increases. Ease when the apparent wind velocity drops.
- Protect from chafe. Make sure spreader and chafe patches are on and in the right place.
- Take sails off the boat when not in use or out of the water for any extended time period.
- Periodically rinse with fresh water. Annual professional servicing and washing is recommended.
- Store sails dry.
- Be sure roller furling sails are well secured when leaving the boat.