A full size JR for a Cavalier 32
By checking the Bermudan rig a little more closely, now with mainsail plus Genoa1, I found their combined area to be 49.6m2.
Then I wondered, could one make a junk sail of that area which fitted on that mast through the hatch, and still with its CE at the Bermudan mast?
I put my secret, but not too accurate formula in use:
SA = B2 x AR x 0.78.
Trying different batten lengths, I ended up with B=5.80m and AR=1.90 (..it helps to have experience with these numbers...)
This gave SA= 5.802 x 1.90 x 0.78 = 49.85m2 .
By assuming that the CE sits on the middle of the boom, I drew up a 5.80m test boom with the middle of it where the other JR (40.1sqm) had it.
This resulted in a mast balance of about 28%. None of my master sails would handle this, but I had made a couple of prototype drawings with yard angle of 55°, which would accept about 25-30% mast balance.
As luck would have it, I had drawn such a master sail with AR = 1.90 (same as Ingeborg is using). However, the lower yard angle would push the CE a little aft of the middle of the boom, so I found its true CE the old-fashioned way; by balancing a printed out sail on a ruler.
This new master sailplan was imported into the Cavalier’s sailplan, and scaled up to B=5.80m. A little cross was added to the boom, representing the true CE. Then the new sail was moved into place on the sailplan.
It surely looked big, now with its accurate area found to be 49.6sqm! However, it is almost identical in size to the sail I had on my Johanna - and she was one ton lighter. The batten length is also the same, at 5.80m.
Thanks to the slightly corrected CE position, the sail was now shifted a few cm forward, resulting in a mast balance of 29%.
As you can see on the diagram, the sail fits well on the mast, and can actually have its mast balance adjusted between 25 and 30%.
Still, I do not recommend this sail, with this high mast balance, until a smaller version has been tested. This is only a study, driven by curiosity, and not a proposal for Graham...
It remains to be found if...
1. ..the sail feathers reliably when the sheet is being eased.
2. ..the boat sails well on both tacks.
3. ..the battens do not S-bend at the mast
This post is already too long so I stop here...
Arne
(.Check Arne's sketches, section 7-44...)