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December 8, 2015 “I am commissioning the new build of a 45 ft Herreshoff Mobjack. I am changing the fore triangle plan to a boomed staysail and a high-cut jib. Because this hull is 17 tons on 39 LWL, would a jib topsail help with pointing and speed?”

David Flynn

December 7, 2015 Quantum Expert Answer

 A jib top is particularly effective for reaching. That's because with its high clew as the sheet is eased the entire sail gets fuller and continues to draw efficiently, whereas a low-clew genoa will tend to twist off aloft. Sailors and sailmakers have argued the double-head rig vs. a big genoa issue for years and the answer always seems to be that upwind, the large low-clew genoa is fastest. Reaching a jib top with the same amount of area will be more efficient, thus faster, with or without a staysail.  

When you have a self-tending club staysail it can be used upwind with a headsail that permits adequate vertical and horizontal "slot" between the sails. The club jib will work with a high clew 85% to 95% LP headsail (often called a Yankee) beating in a good breeze. A bigger headsail will choke off the slot. To go fast and point well in lighter air, you'll probably find the horsepower you need in a big genoa 135% - 155% (rather than a jib top) and you'll leave the staysail furled.

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