Rough set-up

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Here is a rough set-up for the IOM No.1 rig when close-hauled.


Main sail sheeting angle: Get the tip of your thumb between the sheeting post and the boom.

5 degrees
Jib sheeting angle (slot): Make sure you can stick the ends of four fingers between the jib boom and the mast (three if you have thick fingers). 12 degrees

Main sail twist: Have the middle main batten parallel with the boat centre-line, the lower batten pointing in a little, and the upper batten falling off some.  Peter Spence suggests having the top batten falling off the same amount as the main boom sheeting angle -- that is, have it parallel with the boom.  Make this setting without wind in the sails;  when sailing, the leech will open up as necessary. 7.5 to 10 degrees

Jib twist: Have the gap between the leech and the topping lift take at least two fingers.

Or, like the mainsail, have the upper batten parallel with the jib boom.

10 to 12.5 degrees
Mast bend (mast ram): Set the mast curve to nicely match the main luff curve, then straighten the mast a smidgen (OK, maybe 3 mm) to push fullness into the middle of the sail if the wind is lighter than "top of No.1".   

Jibstay tension: Make sure the jibstay never flaps in the breeze. (If you take this seriously, you'll have to have mast pre-bend to obtain the necessary backstay tension.  Or, set your shrouds well aft of the mast and use a "V" spreader.)  
Main draft (outhaul): Get at least a finger and a half between the foot of the main and the boom, up to two fingers. 8%
Jib draft (outhaul): Get at least a finger between the foot of the jib and the boom, up to a finger and a half, but two fingers might be a bit too much. 6%
Jib pivot: Somewhere around 25% of the jib foot, less if you have achieved high jibstay tension. 20% - 25%
Sheeting radius: Make sure the jib boom sheeting radius (distance between pivot point and jib sheet attachment point) is around 10% longer than the main boom sheeting radius (distance between gooseneck pivot axis and main sheet attachment point).  


2022 Lester Gilbert