(Sail Theory Continued)

Center of Effort

The Center of Effort (CE) is the balance point of the total sail area spread around the mast.

To determine the CE of a sail:

Step #1 – draw a line from each corner of the sail to the middle of the opposing side. The CE is located where the lines cross. Each sail will have it’s own CE.

Step #2 – Now that you have determined the CE for the jib and mainsail, draw a line connecting the CE of the jib with the CE of the mainsail as shown below.

Somewhere along this line the CE for the total sail area will be found.

The formula for determining the CE for the total sail area is very complicated and involves and number of variables, all of which are outside the scope of the ASA 106 course and this study guide.

For the purpose of the ASA 106 exam, all you need to do is place a dot along the line that connects the two CEs. Since we are not able to determine the CE for the total sail area, we presume that the CE (for the total sail area) is located just off center favoring the mainsail.

Center of Lateral Resistance (CLR)

Sail theory also requires a look at the keel and the CLR.

The CLR is the balance point for the underbody (part of the boat that gets wet). The location of the CLR is usually only slightly forward of being directly below the CE.

The CLR is generally found near the center of the keel – however, to actually calculate the CLR designers must factor hull shape, length and keel weight. Again, this is something beyond the scope of the ASA 106 course.

Since some weather helm is preferred, place the CLR near the center of the keel but slightly forward of the CE for the total sail area.

For the purpose of the ASA 106 examination, producing a diagram similar to below will be more than sufficient.