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What is the Appropriate "Max Luff" for a Cruising Spinnaker? By Sandy Goodall |
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Question: I'm interested in buying a Standard-Size Asymmetrical Spinnaker. In determining the correct size, is the "maximum luff" the same measurement as my boat's "I"?
Answer: The "I" measurement is the height in the foretriangle. It is the vertical distance from the deck, at the mast, up to the point where the upper end of the forestay meets the mast. If we made the luff of an aspin the same length as "I", it would look too short, since the luff of an aspin flyse "loose" and describes an arc (longer route). In order to ensure that the luff was loose enough to fly properly on a run, we would have to let the tack fly very high, and the sail would clearly look as though the luff was too short. So instead we calculate the aspin luff as something longer than "I". My own method, is to use "I" and "J" to calculate the forestay length, and then add a certain percentage to that. I find this allows the maximum sail area, (which is quite desirable) without the risk of the luff being to long. The logic is that you want the aspin luff to be short enough that in "no wind", with the sail hanging straight down the forestay, the sail won't drag in the water. The resulting length satisfies the two important criteria: 1) This luff length is still short enough that you can stretch the luff as tight as you might want, when tight reaching 2) This luff length is not so long as to drag in the water in no wind |
