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Sam1945
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(new user)
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28/06/2008 20:59
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Jib Sheet Angle
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I am about to rig a new dayboat, and want to know how to establish the correct angle for the Jib Sheets, BEFORE I start drilling holes for the jib sheet fairleads in my new capping rail ! Anybody have any ideas ?
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MBII
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(regular)
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28/06/2008 22:09
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Re: Jib Sheet Angle
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Hi
If you only have the option of one point to lead the sheet to then the standard solution, assuming the jib has pannels, is to follow the line of seam where the pannels join, through the clew to the deck or capping rail and put the fairlead there. This should keep both the foot and the leach tight when the sail is sheeted in. However in different wind strengths and points of sailing the sail will benefit from different sheeting positions. The ideal solution is to use a track so that you can adjust the position of the fairlead to suit. Also the capping rail is unlikely to be the ideal distance from the centreline to create the best slot between the main and the jib.
I hate drilling the first holes in a piece of wood!!
Good luck
James
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Re: Jib Sheet Angle
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Steve Goacher, who knows a bit about sails, reckons that the headsail sheet needs to be pointing at a spot on the forestay 40% up the luff of the sail.
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Re: Jib Sheet Angle
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If you don't want to fit a track, you can always put the fairlead further aft than necessary, and haul the angle of the sheet down by using another small block on an adjustable rope lead up from a cleat. These are called "Barber-haulers" on dinghys and Lizards on real boats. Very low tech, but they only attach at two single places, dispensing with the need for a track. Tracks and cars are more 'scientific' but as I suppose your dayboat is a bit trad., the lizard system may be more practical and allows for a lot of adjustment if you like trimming your sails. The only problem is that in light airs, the weight of the block will drag the lead down and may close the slot between the jib and main too much. Not a problem with a track.
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Re: Jib Sheet Angle
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You have two angles to consider here; the angle between the deck and the sheet, and the angle between the centreline and the sheet at the jib tack. Bisect the angle at the clew and draw a pencil line on the sail. This line extended along the sheet will give equal tension to leech and foot. If the sail has a mitre seam, and not all jibs do, then it may be along this line. In the horizontal sense, on the deck, a line 12 degrees from the centreline should take you to the sheet fairlead. Barber-haulers are most commonly used to reduce this angle temporarily if required.
Peter.
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Re: Jib Sheet Angle
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Of course, leaving aside all the technical drawing skills, all you need to do, as it's a day boat and presumably doesn't have large sails, is to go out on the water and sheet in the sail from the cockpit then play about holding the sheet down in different spots until you find the ideal where the leach neither opens too much or goes too flat and the foot curves nicely without being too straight.
After all, that's what you are after, a nicely set sail and no amount of calculations will guarantee it'll be right in practice.
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Re: Jib Sheet Angle
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The options are more limited with the jib than the staysail, because the jib has to be sheeted in outside the staysail, yet at a point where the boat is narrower. Sheeting further aft to some extent overcomes this, but at the expense of more difficulty getting the loosened sheet to pull freely round the forestay when going about.
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Sam1945
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(new user)
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30/06/2008 18:57
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Re: Jib Sheet Angle
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Thank you all for taking the trouble to reply to this topic. There is a wealth of info here. I shall be doing some technical drawing soon, but also taking Lake Sailors advice and playing about on the water to confirm it all.
Thanks again for your generous help !
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