Sail Making
I hope the first article was some help in understanding sail design. Knowing how Camber is formulated does have a impact on how a sail performs. With that there is another important factor in sail making, it is plotting a sail's Draft Location.
Draft location is the area of maximum Camber along the length of a sail. This Draft location provides the sail's aerodynamic efficiency. If ignored, the sail loses power, hence you heighten your chance of losing races! Not good.
So, what is correct Draft for an R/C model yacht sail? That depends on the yacht the sail is for or personal choice. The popular point is 40% aft from the luff. Now, how does one obtain a proper 40% Draft location? It is easier than one thinks. Now comes the fun.
Before starting, make sure you have and understand the boat class sail specs to avoid any problems. Once you have a basic triangler sail design drawn on paper, there are a few steps that needs to be done. For 36/600 class sails, the standard panel size are 12" wide with an overlap of 1/8" to 1/4" for the tape seam. Start with the lowest part of the sail, mark the first seam line 90 degree to the leach line. This first lower panel seam should be around 4" to 5" up on the triangle line and clear the corner patches. This will start the Camber in the sail.
From there, measure up 12" on the triangle line and draw another panel line. The top sail panel's length will finish out to what ever is left over. A 36/600 main sail should have 5 panel seam lines and the jib 4 seam lines. This part of the project is important, so take your time and use a pencil, you maybe doing some erasing. See figure 1 for details.
To find a sail's Draft location is a simple process. For each seam line, the Draft location will be at 40% in from the luff. To do so, measure the width of the sail at the seam. Then with the measurement, multiply it by 40%. The formula is as follows: Width x Percent = Draft location. For example, the width of a seam is 10" 3/4 (you will have to convert the fraction to a percent by dividing the numerator by the denominator). By multiplying 10.75 by 40%, the results are 4.3 inches. At that point on the seam is the Draft location of 40%. See figure 2 for details.
With that in mind, do the same measurement and calculation on the other seams to find their 40% Draft locations. If all measurements and calculations are correct, draw a line through all seam's Draft locations on the sail. Now you have establish the sail's Draft location. See figure 3 for details. Well, that is it for this issue. I hope the information well help you understand this stage of sail design. So go ahead and look it over and start your own sails.
