The moment you reef a headsail you lose some of its design attributes, and if you view sail efficiency as part of overall seamanship - which you should - then finding ways to improve the performance of your headsail is important. An average headsail has the maximum draft located at a point about 33 to 38 percent aft from the luff. Therefore, as soon as you roll the sail up, even a little, you roll away the ideal shape and end up with a compromise. Furthermore, as the clew rises the center of effort gets higher as well, precisely at a time when you would prefer to have it lowered to reduce heeling moment. You cannot do much about this, but you can modify your deck layout to ensure that your genoa is trimmed properly and performing effectively.
Start with a sail that has the correct clew height and then modify your deck layout so that you can move the sheet lead position to accommodate clew location as the sail is reefed. Each sailmaker has his own idea of where to place the clew. Those with a racing bent like it low, whereas classic cruisers, for example, those with traditional-looking schooners or cutters, like it high. In the end it really depends on your sailing plans and the kind of boat you are sailing. For most cruisers the clew height should fall somewhere between the two extremes, since there are benefits to be gained from each. A low clew, for example, provides the best upwind performance since the shape is more consistent throughout the sail, the center of effort is lower and you have a short, sure sheeting point. On the down side, the moment you reef the sail, your sheeting position changes (Figure 7.8) and unless you have a way of adjusting the sheet lead, you quickly lose all performance.
With a high-clewed sail, on the other hand, you can reef the sail and even without much adjustment to the lead position you will end up with a decent sheeting point. The problem is that high-clewed sails are fairly inefficient for windward work, although they are fine for reaching and work well with a staysail. Again, it is a matter of preference. My ideal sail is one that has the clew high enough so that there is good visibility under the sail but low enough that the sail retains some of its performance ability. You also need to allow room for waves crashing over your bow to pass easily under the foot of the sail, and you need the clew low enough so that you can adjust the leech line without hanging over the lifelines.
If your deck layout does not already allow you to adjust the sheet lead position while under sail, modifying with modern deck hardware is a simple matter. Replace your car and track with one that can be adjusted under load, and add a line that runs from the front of the car forward to a turning block, and then aft to a winch. This allows you to drag the lead forward, or ease it aft. As soon as you reef your genoa, the clew travels forward. Sails with lower clews need a sheeting position adjusted sooner and more often. The same applies when you ease the sail out when sailing on a reach. If you do not move the lead forward the clew rides up and spills wind from the leech, depowering it and losing most of its efficiency. Having the ability to adjust the car position is crucial to overall performance.
The headsail adjuster on the Reichel Pugh 70 Mojo worked perfectly, especially so because the clew of the head-sail was fairly high off the deck.
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