JIb luff control systems

[Phill]

Peter, You ask a good question that gets very involved, but I'll try.

'Normal' forestay vs jib halyard tension is best compared to Mast vs cunningham tension on the main. We set up our mast bend to best match the luff curve built into the main, to set the overall depth/power for the conditions. Then we adjust the draft position with the cunningham and or main halyard. If we compare the forestay to the mast, the forestay (overall rig tension) will determine the sag (bend) that we want to match to the luff curve built into the jib. With that 'set', we then adjust the jib's draft position with the halyard or cunningham (sometimes called 'jib cloth') tension. Those boats that use a jib luff wire can use halyard tension to replace the forestay as the load bearing wire, effectively becoming the forestay, when the jib is hoisted.This gives them the ability to power up or depower the jib during a race. We used this system in the 470 class, the forestay was only for keeping the mast up when the jib was not hoisted. With the jib up the forestay went so slack that it fell about 4" back and laid against the jib. However, with that system, a jib cunningham is required to then adjust the jib's draft position. When a jib luff rope is used, the forestay (rig) tension determines the jib luff sag (power). The jib halyard can then be used to adjust the draft position, because the luff rope streches, making a jib cunningham unnecessary. However, rig tension is not legally adjustable during a race. So once set, the overall draft/power of the jib can not be adjusted.

The advantage of jib luff wire and cunningham is better adjustability.
The advantage of jib luff rope is simplicity. ... With more complex interactions. Main sheet, Vang, wind velocity and traveler can all add/subtract tension to the overall rig and effect the jib sag.

On Lollipop, my first sails had a jib luff rope . I originally used a 3/1 purchase, ( the very one I loaned to Andy ) to tension the halyard. My reason for this was to just get out and race. I planned to 'fix' my control systems after seeing what the hot sailors were doing. 17 years later, almost nothing has been changed from my original simplest versions.
In the jib system complex interactions, it seems that as the wind veloicity changes, the mainsheet/vang tensions, add and subtract to the rig tension proportionately in the correct direction, making the sag adjustments sort of automatic. In any case, I am happy with the simplier systems.

Hope the makes sense, and helps.

phill

[KaiB]

Ahh...once again, thanks Phill.

So you set rig tension (both side and fore) to establish a pre-bend to match daily condition?

Once this is done, you've got halyards (main and jib) out- and main- down hauls and vang (as well as traveller and barbers) to adjust on the course.

Am I getting warm?

Fair winds, Kai