January 29, 2016 “I have a Hunter 31. The maximum heel I want to sail is 22 degrees. I have 110% and 135% genoas. I usually take a beating when racing in wind of 20 mph or more, so I would like a headsail that will handle those conditions. I have a new Quantum membrane main that can be flattened quite well. I need something smaller than the 110 and a double-reefed main in 20+ mph. I only have six inches left on my jib car track forward of my jib car when sailing the 110. It seems that the 135 points better than the 110. My thoughts are to keep a longer LP and shorten the luff to the top of the main when double reefed. I have seen boats with shortened jib luffs. Which would be the most efficient way to go? Shorten the luff or a smaller LP?”

David Flynn

December 7, 2015 Quantum Expert Answer

Probably a little bit of both. Once you decide on a target area, reduce both proportionally. As you reduce the LP, the clew will have to rise for the lead to stay on your track. Designed clew height should not get too high (3'-4' max if track allows) as this will begin to compromise upwind ability. Reducing luff length works well, especially in the interest of maintaining a reasonable aspect ratio (height versus width). If the sail gets too tall and skinny, it is hard to control the twist and overall shape. The downside is that the luff is the most efficient part of the sail in terms forward driving force (the back of the sail creates more sideways force). 

As in many things, balance is the answer. A Quantum sail consultant in your area will be happy to look at your actual measurements and sail sizes to help you determine the geometry that best balances the trade-offs. Based on your description, it sounds like the right solution might have an LP of around 85%, and a luff length shorter by 2-3'.

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