Topic : 2:1 Jib Halyard fixing

Can anyone shed some light on the best place to locate the tail of a 2:1 jib halyard?

I have noticed that on some masts the fixing is below the jib halyard block, on others it is off the bottom screw on the spinnaker block. In the later this means that the load is below and above the hounds - the jib block being below and the spinnaker block being above. Not being a mech eng - would this mean that the sum of the load could potentially end up at the hounds? (In the middle of the two)

Would this give the effect that the rig is less prebent?

Is this good/bad?

Any comments appreciated.

Posted: 31/05/2005 16:02:44
By: Carlw
Prebend, the critical thing is to match mainsail luf curve to initial mast prebend, then the higher the shroud/forestay differencial the higher the bend bocomes as the loadings mount. So in theory as the breeze increases the shroud loading above that of the forestay induces fore & aft bend and flattens the main & dumps excess power.You'll understand that the mains luff curve has to matched exactly to that of the mast
Like all things in sailing this is just one avenue of achieving your goal

Posted: 31/05/2005 21:34:39
By: Barry Watkin
OK - this suggests that prebend is controlled by the shroud/forstay differential and spreaders will help to control it further but are less significant to the equation?

What I'm trying to say is that the rig is prebent if the shroud forestay differential is great enough regardless of where the spreaders are.

Posted: 01/06/2005 09:15:00
By: Onlooker
Barry, help me with this. If the pre-bend of the mast matches exactly the luff curve, then wouldn't the sail be exactly flat and thus generate no lift up wind at all?

Posted: 01/06/2005 09:54:51
By: Alan
Point 1   Spreaders, moving the tips aft will increase prebend set up, this is the most common & widely accepted way of tuning fore & aft bend once the rig has been set. It is generally accepted to be 20-40mm (less for heavy weights,more for light) On old alloy rigs some used 'hook'
shroud to mast terminals to vary the shroud height/forestay diferential according to the conditions.
Point 2, Luff curve is just one part of sailmaking, the seems are cut to an areofoil to produce what is called 'broad seeming'. It is the combination of luff curve & broad seeming that produces the desired shape.
You have hit the nail however if the mast bends more than the luff curve built in the sail you will get horendous creasing from the clew radiating out to the luff.

Posted: 01/06/2005 14:43:35
By: Barry Watkin
Barry thanks for that, - seems the collar on the mast won't let the hounds go any higher - so the setting on the spreaders is going to be v-significant if the dead end is placed on the bottom of the spinnaker block.

see also - chairmans comments on Tom's mast I think 70mm above

Posted: 01/06/2005 17:14:37
By: Carlw


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