Jes,

since my sails generally have a lower section with parallel battens and with the luff and leech parallel to the mast, I define the mast balance of my sails to be the number of percent (of batten length B) that the lower battens protrude forward of the mast.

Arne

PS: The lower mast of my Frøken Sørensen had a section of Ø100 x 4mm. I bet that is enough for your boat as well.

(EDIT: Now I'm not so sure: Jester Challenge  -  see later posting...)

This summer JRA member Paul Schnabel has successfully cruised his Maxi 77 with his junkrig set with up to 27% mast balance.
I have therefore made use of his findings and drawn a hi-balance sail for the Corribee, shown below.

The mast was put through the hatch, with its centre about 200mm aft of its forward edge.

I don’t think the sail will ever need to be moved forward of the shown position. If anything, it rather needs to be shifted aft a little to trim away any lee helm. There will be plenty of room for that.

The Corribee has a smallish rudder. This hi-balance JR brings its CE quite close to the JR mast, which again means that the CE will sit close to the boat’s centreline when sailing downwind. This should help the rudder to cope.

Just an idea.

Arne

PS:
It looks to me that the superstructure of the Mk 2 and 3 are very similar, so I used a Mk 3 version here.

(Hi-res diagram in Arne's sketches, section 8, photo11)

Good, Jes.
Have you figured out where to put the mast?

Arne

Jes,

can you tell us which mark number of the Corribee you have?
Moreover, what sort of sailing are you planning to do?

Arne