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Location: Annapolis, Md
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Re: Small main sail, large jib - questions
This topic seems to crop up around here from time to time, often with very strong opinions on all sides. As my esteemed fellow moderator said, with skill, care, and good crew work the short comings of these rigs can be tamed and made manageable, especially in a 24 footer. But I tend to look at big jib-small mainsail rigs from a different perspective.
If you look at the evolution of sailing rig proportions, when you look at small working craft, cruising boats until the CCA and IOR racing rule era, race rigs on boats before and after the CCA and IOR race rules, the norm was large mainsails and small jibs. If you look at wind tunnel testing that seeks to compare drive to sail area, as a broad generality a fractional rig with larger mainsail, and smaller minimally overlapping jibs, tends to be more efficient than the small mainsail, big jib sail plans.
So if this true, why does the big jib-small mainsail rig exist? As Faster noted this rig resulted from designers trying to create a rig that was faster than the race rule expected. In this case the rig proportion came from a rule which under measured the sail area related to the leech of a headsail. It resulted in boats that relied on huge jibs to sail in light to moderate breezes, but which were quickly overpowered as the wind increased. As Faster notes, initially this can be addressed by under trimming and eventually 'flagging the mainsail', but at some point there is not much you can do to keep the boat moving and under control. The net result is that the headsails on boats like these have very narrow wind ranges. For example, an AP 150% genoa may have a workable range between 2-3 knots apparent and 12 or so knots apparent, and at the upper end, the main is typically undertrimmed. If I look at the headsails on a boat like mine (and I only cite my boat since I know it very well) my AP 109% minimal lapping genoa has a range from 2-3 knots apparent up to around sustained 25 knots apparent (with a single reef in the mainsail).
Consequently, because the headsails are used for a much narrower range of windspeeds, these boats need more frequent sail changes and so are less suitable to dealing with a building breeze shorthanded. Because these headsails are so big, the ability to adapt to building breezes by furling the jib becomes more limited as well. Most times these boats are casually sailed with something like a #2 genoa. The problem here is that these sails lack capability at the lower end of windspeed range (say less than 5-8 knots). To be fair, that simply many not be a problem for many people since many casual sailors tend to motor at this lower end of the windspeed range anyway. The other issue is that it is simply harder to drag these larger overlapping sails around the shrouds, and baby stay, making tacks way less convenient short-handed.
In a general sense the issues associated with this rig proprtion was not so bad on a well crewed race boat. But for short handed sailing, even on a small boat, these rigs are very inconvenient. And while efficiency and ease of handling are not an end all, to me, if I were looking for a different boat to own, while I still had a choice of picking a rig for easy handling, I would have a very hard time seeing these big jib/ small mainsails as the right choice.
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Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay
Last edited by Jeff_H; 12-13-2012 at 09:02 AM.