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Old 17-02-2009, 08:50   #31
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Different Ships Different Long Splices

In his last post Jim Cate is correct as to the effect of the Vang except, I believe he ment to refer to the "clew" rather than the tack. Tightening the vang forces the boom down, regardless of the set of the mainsheet, tightens the leach and takes some of the twist out of the sail. If the the sail is continuously attached to the boom, with a bolt-rope in a slot or with slides and shackles, and the sail, designed for that type arrangement, has not been stretched out of shape by, for example, someone taking a reef fore'n aft (slab reefing) without properly fixing the bunt-lines, tightening the vang also flattens the belly of the sail and will do so quite markedly on some boats.

As to whether sail slides load a boom or not, that depends upon the design of a sail and its condition. Some argue that a loose footed main is preferable as it permits the sail to be shaped more readily, similar to the Genoa. Others argue that since the Main does not have the benefit of the "end-plate" effect of a deck as does a genoa, attaching the foot of the sail to the boom reduces reverse-flow under the foot of the sail from the windward to leeward side which reduces the efficiency of the sail, more or less so depending upon the aspect ratio of the sail. In my day, most mainsails were continuously fixed to the boom and most racing sails were designed with shelves and "flattening reefs", which definately required that intermediate bunt-lines (or reefing lines) be taken up to avoid damage to the sail.

As to whether one can readily relocate a mainsheet, it would be wise to have a qualified engineer run numbers on a boom as, particularly if a sail is loose footed, moving from end boom to mid-boom sheeting substantially increases sheet loads and can dramatically increase boom loading with bending moments that would not otherwise exist.

FWIW...

s/v HyLyte
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Old 17-02-2009, 09:05   #32
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The vang applies load in more then one direction. It pulls down the leach of the main at the same time it tries to drive the boom horizontally through the mast. If the main is loose footed or a shelf foot you are not going to see any support along the length of the boom, if the main has a standard bolt rope it will minimally support the boom.

If you are going to break the boom do it the right way, rig a preventer forward from the center of the boom and the stuff it in the drink on a power reach. It'll break.
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Old 17-02-2009, 09:09   #33
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Oooops

"In his last post Jim Cate is correct as to the effect of the Vang except, I believe he ment to refer to the "clew" rather than the tack"

Dang, I hate it when that happens!!

You are so right Hylite. Thanks for pointing out my error... shows what happenswhen you do this stuff first thing in the morning!

Cheers,
Jim
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Old 17-02-2009, 09:29   #34
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'sokay Jim--Most people don't have a clew about the matter anyway!
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