Jib Sail Shape

On almost all sailboats, the block on either side of the boat through which the jib sheets lead is adjustable so that it can travel towards the bow or stern and be locked in any spot along the track. It is this lead that determines the shape of the jib. If it is too far forward the foot of the jib is too loose and the leech too tight, because most of the pull on the jib sheet is downward. If it is too far aft, the foot is stretched tight and the leech too loose because of the backward pull. What we want is a compromise between the two extremes, so that the sail is not distorted.

There should be an even flow of air on both sides of the sail at all levels along the luff. In other words, the sail should have a constant angle of attack to the apparent wind. If the lead is too far forward, the bottom of the sail will have a big curve in it and the lower luff will line up with the wind before the upper part does and will luff first. Conversely, if the lead is too far aft, the leech will be loose and tend to fall off up high, causing the sail to luff first at the top. So the test to determine proper jib lead placement is to head the boat up slowly until the jib begins to luff. If it luffs at the top first the lead is too far aft. If it luffs at the bottom first, it's too far forward. But if it luffs the full length of the sail all at the same time, it's set in the right spot.

The wool telltales on the jib are more sensitive to angle change than the jib itself. In other words, you can see the windward one flutter before you can see the sail start to shake along the luff. If you have three sets of these telltales, (in three positions along the luff of the jib about six to twelve inches from the leading edge depending on the size of the boat), you can see which one flutters first and whether your jib leads are in the right place. The telltales also allow you to make the same lead judgment by watching for a stall. If the bottom leeward one flutters first, the bottom of the sail is stalled, meaning that the sail is too flat at the bottom because the jib lead is too far aft. With three sets of woolies your crew can more readily catch a change in the situation due to an increase or decrease in wind velocity and change the jib leads fore or aft accordingly.

Experiment to reduce "twist" and curling of the leech to windward, so that, when the boat is turned into the wind, the jib luffs all up and down the forestay at the same time.

Steve Colgate is the founder of Colgate Sailing Schools, with locations in Tortola BVI, Captiva Island FL, Duck Key FL, St. Petersburg FL, Chelsea Piers NY, Liberty Landing NJU and Newport RI.

Offshore Sailing Schools
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