Sheeting angle

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Colin Helliwell
Joined:18 Jun 2014, 18:44
Sheeting angle

Post by Colin Helliwell » 22 Aug 2014, 20:53

The plans for my [ageing] Nimbus show the sheeting coming through at deck-level and through a fairlead to the boom. Other pics I've seen of (probably more recent) IOM designs often feature a ~2cm pillar fairlead through which the sheet exits. I was drawn to that at first - it keeps the pull purely in/out, not pulling the boom down, more controlled. And yet - since the kicker isn't adjustable - I'm wondering if that is best. When the boom is out you want a little less kicker-action, more so probably when sheeted in. So is an always-horizontal sheeting angle best? Why is the 'pillar' popular?
*** I'm not trying to be controversial, or slate accepted practice! Just coming at this from full scale, and seeking to understand the principles which apply here. Keen to learn. ***

Joined:06 Jan 2006, 00:47
Sail number:CAN 307

Re: Sheeting angle

Post by Hiljoball » 25 Aug 2014, 05:42

Hi Colin, as no one else has replied on this, I'll have a go.

I think you are referring to a 'sheeting post'.

On a big boat sailing close hauled, the main sheet controls the twist in the main and the traveller is used to control the angle of attack - the sheeting angle. As the traveller is let out towards the rail for a close reach,it cannot go further and so the vang has to take over controlling the twist of the main and the main sheet takes over controlling the angle of attack. By setting the twist with the mainsheet, the traveller can be pulled to windward to bring the boom close to center line. Without the traveller, the downward pull of the main sheet would over tighten the leach.

In IOM, we are not allowed a traveller. So we use the vang (and mast ram) to control the twist in the main, and the main sheet only controls the angle of attack. So the sheeting post is used to raise the sheeting position to be only an inwards force, with no downward component. Some clever skippers may set the height of the sheeting post a smidgin lower (that's tech speak) to allow a downward pull component at extreme close hauled for a high point mode - but the risk is closing the leach and stalling the main. So the sheeting post and vang combo allows the boom to be pulled close to center line without over tightening the leach.

John Ball
CRYA #895
IOM CAN 307 V8
In my private capacity

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