One of the most important things you should know about your mainsail is that it's the back of the main that works with your keel to provide lift when you are sailing to windward. This single fact will have a bearing on the shape and size of your sail, which in turn will influence the fabric and panel layout you choose. The back of the main becomes less important once you bear away, for then propulsion becomes more a factor of projected area than aerodynamic shape. But even cruising sailors who try their best to keep the wind at their back, need to go to windward on occasion. So if windward performance is what you want, then remember the roach. In this article we will take a brief look at sail plan configurations and how to achieve an optimum mainsail by choosing the appropriate size, fabric, and panel layouts.
For the last 10 years there has been a trend toward in-mast furling mainsails. It's impossible to argue against the convenience of push-button sailing and rolling the main into the mast to reduce sail is certainly a convenient way to go. The drawback is that for the main to roll away, you can't really have much sail area that extends beyond a straight line between the head and clew. It's true that you can gain a bit of area by having vertical battens (the kind often utilized in stowaway mains), but this is a token amount and hardly worth the aggravation of battens that roll up.
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By extension, it can be argued that boats with rollaway mainsails do not have good windward performance, which in turn could lead to problems, especially if you are trying to sail off a lee shore. Now, I am not trying to be an alarmist (although last summer I did have a problem off the Azores Islands because of a sweeping current and a lack of pointing ability), but if you are looking at mainsail choices and considering sail plans, you might want to consider what I view to be an optimal configuration: a large mainsail with power in the back end, and small, non-overlapping headsails, each using the latest sail handling systems like batten-cars and lazyjacks to help with the main.
There are very few pure-cruising sailors who relish their time at sea and don't care how long it takes for them to get to the next port. The rest of us tweak and trim our sails to get better performance, hoping to save at least a few hours on each passage. We all look for and expect performance from our boats and it's the sail plan that provides it. Lighter, stronger, and more exotic fabrics are relatively new to the cruising market where DacronTM has long dominated, and there are good reasons for this. DacronTM is rugged and reliable, and despite stretching a little over time, it has proven to be the best fabric for those planning to go offshore. One drawback has been that as boats get bigger, the loads become greater, and the sails get heavier. But now, exotic materials are able to make sail handling easier, as well as making sails look better and last longer. The only problem that remains is that the profusion of choices complicates the sail-buying process and confuses sailors.
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As far as I am concerned, for cruising boats up to 50 feet in length, there are really only two, or possibly three, fabric choices. This is based upon my experience making many sails that have performed well over a wide range of conditions for many years. The aforementioned durable Dacron
TM is a staple in the sailmaking industry and it goes without saying that, you can't go wrong with Dacron
TM as a basic choice. For a more performance-minded sail, consider Pentex
TM or a polyester cruising laminate. We discussed the pluses of Pentex
TM in the first two articles in this series, and how the fibers are used in a laminated fabric (Review
Part One or
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With such well-advanced engineering, most sailmakers will have no problem building you any size or shape mainsail. Full-batten sails with lots of roach are becoming more common on cruising boats where performance is desirable. And where fabric was once a limitation, it's now an advantage. In the next article we will look at all the features that make your mainsail easier to trim and handle, and how you can incorporate them into a new sail. As I have already pointed out, it's called the mainsail because it is the main component in your sail inventory, so it's certainly worth getting it right. And doing so will make your sailing safer and more enjoyable. 
