First, if this is for a cruising spinnaker or asymmetrical spinnaker, give us the headstay length and the I measurement of the boat. the (I) measurement is the height of the mast from the deck to the top of the mast. If you do not know, take a long tape measure and attach it to the main halyard and send it up. Next, give us the (J) measurement . This is the length from the bow or tack point, to the front of the mast. See the diagram below for an example.
For a traditional spinnaker, this is what we need. First, (1) measure the stay length. Again, use the tape measure and halyard to send the tape up the stay and measure it. Next, (2) if you have the old spinnaker, lay the sail out and measure the maximum width of the sail. Last, (3) measure the foot length of the sail as seen in the diagram. Please note, that there is extra cloth from the straight line you have produced with your tape measure. This is called FOOT ROUND, and can be measured in inches from the straight line to the bottom of the sail.
With these measurements we can produce a sail the same dimensions as your old, or we can produce a new one that will be in regulation with racing rules. Sail cloth is usually nylon and if you know what it is, let us know. Most racing spinnakers are 3/4 oz. or 1/2 oz. nylon. If there are special panel arrangements, put this under panel cut in your form provided. Of course, colors are very important and must be established with the panel arrangement.