FURLING GENOA MEASUREMENTS
First, try to measure your old sail by stretching it out over a flat surface. If this is not easily done, try using a long tape measure and measuring the sail while it is on the boat. This could be difficult on a windy day, but if space is a premium, this can work.
Now, go to the sail record and find the measurement page. Using your long tape measure, measure the (1) luff length. This is the length of the front of the sail from the tack eye, to the head of the sail.
Next, (2) measure the foot of the sail from the tack eye to the clew eye. The tack is at the bottom of the front of the sail marked luff and the clew is at the bottom back of the sail.
Measure the leech (3) of the sail by measuring from the head of the sail or top, down to the clew of the sail. Notice that the leech has an inward curve.
By measuring the depth of the curve from the tape measure, into the true edge of the leech, you will get a number in the range of 4 to 12 inches or more. See the diagram and you will see that the maximum depth or "hollow", is approximately 50 % of the length of the leech. This is where you would measure the depth for the leech hollow. Getting back to the foot of the sail which you have measured already, this also has a curve we call "rounding". This is the depth of the foot from the true straight line out to a final curve. See the diagram for an example and you will see the maximum curve is approximately 50 % of the length of the foot.
Cloth is a subject best left for the sail maker and how and where you will be using it. Dacron has many different weights and thread weaves. If you desire just a simple cross cut sail, then there are many to choose from. Laminates. can also be an option in a radial design. Also with a radial design, you can mix weights of cloth for maximum strength and less weight overall.
Last we need to know the fittings that are on the sail. How it is attached headstay, foil or furling unit. The form is there for you to understand where to measure and to fill out. Remember if you measure carefully, you will have a sail that works well the first time it is hanked on the stay.