IMPORTANT: Measure your rig's maximum dimensions. Our sail designers will make the proper allowances for stretch and hardware.  
"P" dimension: Use the main or mizzen halyard to hoist a tape measure up as high as it will go. Record the distance from the peak to the top of the boom.
"B" dimension: Measure from the tack pin of the gooseneck to the point of maximum outhaul travel.
Please note the type(s) of sail tracks on your boat's mast and boom and enter the info on the GET A QUOTE form

The mainsail is the workhorse of your boat's sailplan. Because the mainsail is up virtually all the time, its fabric must be light enough for sensitivity in light air and tough enough to withstand the extreme loads of high wind. The mainsail must have an airfoil shape that covers the range of wind strength you sail in, it must drive the boat on all points of sail (not just to windward), and it has to maintain its airfoil shape when reefed. Finally, the mainsail fabric must be as supple as possible for easy handling by shorthanded cruising crews - the stiff fabrics favored by racing sailors can be a nightmare for cruisers.
  Because cruising boats differ in size and type, and their owners differ in the way they use their boat, we offer a number of panel layouts (each available with the batten type of your choice) for cruising mainsails. While there are no hard and fast rules, each panel layout is best suited to certain size boats and primary uses.

A tried-and-true panel layot for small to mid-size boats and all types of cruising. Fabrics for crosscut mainsails are well proven, low stretch, and available in many weights.
Good for small to mid-size boats. The vertical cut eliminates load-bearing seams along the leech edge. A good choice for battenless or in-mast furling mainsails.
Best for boats over 40 feet. The tri-radial design keeps stretch to a minimum and allows lighter cloth to be used in the low-load center sections, and heavier cloth in the high-load corners.

Good for mid-size to large boats. Radial design allows "step up" cloth weights - heavy along the leech area, lighter along the foot and luff sections.
Best for smaller, performance cruising boats where less stretch than a crosscut panel layout is desired. Also well-suited to battenless or in-mast furling systems.
What type of battens should you get? Here's a quick rundown. Conventional-length battens are easy to handle when hoisting and furling the sail, but long-distance cruisers find them susceptible to chafe and point-loading of the sail at their inboard ends. Full-length battens give superb sail shape and stability to the mainsail, but they require the installation of battencar sliders or tracks, and care must be taken when hoisting and furling the sail. A Battenless mainsail is zero-maintenance, but about 15% of the mainsail's area is sacrificed due to the necessary "hollow" that must be cut into the leech.

(Please Note: We cannot supply full-length battens
because they exceed the allowable length for shipping.)

How many reefs should you get? A general rule is: Weekend sailing = 1 reef; Coastal Cruising = 2 reefs; Bluewater Cruising = 3 reefs, or 2 reefs and a mandatory storm trysail.