First, take your main either laid out over a flat area, or raising the sail on the mast. Use a long tape measure and measure the (1) luff of the sail. This is the length of the front of the sail. Be sure you have the sail stretched out well to keep the measurement accurate. If you are using the mast, send the measuring tape up with the shackle of the halyard.
Next, you can measure the foot of the sail(2). Use the same technique to measure the foot of the sail as you did for the luff. Give us an idea of how much rounding you have on the foot. “Rounding”, or foot round is the curve of the foot of the sail.
Leech length (3) can be measured the same way as the luff. Take the tape measure from the headboard to the clew. Notice that you have extra cloth if you stretch the tape tight toward the back of the sail. This extra cloth to the main is called “leech roach” This extra cloth gives the sail more area, and is well supported by the battens of the sail. Measure this in the area of each batten. This will give us the amount of extra cloth given to the leech of the main.
Battens, are not always the same for each sail. Measure the length of each batten or batten pocket (5). Also give us an idea of how wide the pockets are and how long they should be for that perfect fit.
Your headboard is the support for all of the extra cloth on the back of the sail. Measure the top of the headboard for the width of the head of the main. Let us know what type of material is used for the headboard, nylon or metal. The mast will have some sort of bend as you look up from the bottom to the top. This is called Spar or “mast bend” (7). By using the halyard, you can gauge how much bend you see , if you look up from the base of the mast. This measurement is in inches and the most bend you may see is about 50% up and can range from 2 to 6 inches. This is how we produce the correct “luff round” so it fits well in the front of the sail and matches the bend in the mast.
We must know the type of mast slug you have for your main, for they vary in size and shape. They may be flat, or round with either webbing to attach them to the sail or shackles. We have a fair way of gauging sail cloth, but the more we know about the sail and how it is to be used, the easier it is to replace it and make it correct the first time.