Letter to the Editor:

Refer to Bill Fastiggi’s article "Genoa Trim Made Simple"

n 1981 North Sails made a video entitled “The Shape of Speed”. It featured Lowell North, John Marshall and Dick Deaver. When it came to trimming the genoa, North took the spotlight and narrated:
“The keys to the best sheet lead positions are the genoa luff tell tails. As the helmsman slowly luffs up, all the windward tell tails should luff at the same time. If we see them break first near the head while the lower ones are still streaming, we know that the head is not trimmed hard enough and the lead should be moved forward.”

It is easy to understand the physics behind North’s guidance for genoa trim - the entire sail should keep pulling right up until the maximum point is exceeded. The physics behind Fastiggi’s idea of trimming so that the top tell tail luffs early is less obvious, for it implies that there is a range near the maximum pointing angle at which the upper part of the sail can be luffed while the lower part keeps pulling. That such trim can produce as much or more thrust as the North criterion and needs to be explained.

Tom Simkins

Response by Bill Fastiggi:

Dear Tom,

There are many ways to go about trimming a genoa, however this is the trimming technique that has proven fastest on most boats with modern sails. Set the jib leads so that the foot of the sail touches the shroud base at the same time or slightly before the leech of the genoa touches the spreader tip. Sail trim will then range from 2" to 12" off the spreader, depending on many factors; type of boat, wind velocity, wave heights, etc.

If the leads are moved forward, more tension is applied to the leech and less tension to the foot of the sail. This will add power to the sail making the upper leech more closed and provide a greater depth of chord in the lower third of the sail. If the jib leads are moved aft the lower third of the sail is flattened, and the upper leech will twist open.

One of the most important factors is achieving the proper sail shape is the amount of leech twist. The above method is the easiest way of getting close to the correct amount of twist, however it is different on every boat. On most boats when this method of trimming is followed, the upper telltale will break first. On most boats, because of narrow sheeting angles, relationship of chord depth to chord length, and draft position in the sail, this will provide the optimum trim. In many cases when the tell-tales break evenly, the upper genoa leech is too closed, and will cause excessive backwind in the luff of the main, too much shape in the bottom of the sail, and the boat will go through the water at a slower rate of speed.