Bonsoir

So sorry to learn that, Arne.

Take care.

Eric

Sorry to hear that, Arne - I hope you can get back on your feet and out of there soon!

Andi, in Arne's absence, I had better just confirm what Graeme says: if you can find the CE of your current rig, and it's satisfactory for helm balance, then you can safely put the CE of the JR in the same fore and aft position. The PJR recommendation really only applies to the flat sails that they were using way back then. The cambered sails that we use these days work pretty much like the cambered sails of any other types of rig. Also, it's safe to say that the actual centre of pressure on the underwater body migrates quite a bit fore and aft on your long keeled hull, in different sailing conditions, so it's somewhat of a dark art to decide where the sail CE should be placed. Most JR sail types are happy to be shifted fore and aft across the mast to a certain extent, so you have some scope for fine tuning the helm balance.  

Welcome to the JRA Andi.

I am not an expert. I think if you can wait a little while you will probably get a better answer than I can offer.

Drawings based on photographs are problematic.

Assuming your boat was satisfactorily balanced on the helm with the original rig, then I see no reason why you need to go back to first principles in designing your new rig. By this I mean, no need for trying to make a hull profile or to calculate CLR.

Assuming you want a single sail rig, here is what I would do. You have the sails, so you can measure them. You have an existing mast position. You should then be able to make an accurate drawing of the old sail plan. Calculate it's geometric centre (CoE).

The new junk sail needs to be placed on your drawing so that its geometric centre is on the same vertical line as the old geomtric centre.

In deciding where to place the mast, you will need to have a junk sail planform in mind, with an appropriate mast-balance and yard angle.

The best advice I can give is to wait until one of the more expert members can chime in. In the meantime, go to the Members' Area of the website and navigate to "Technical articles". Members'Area/Documents/Technical Articles.  Select "Arne's Files" and read the first four chapters.

Arne has a suite of sail plans with a range of mast balance ratios and aspect rartios with suitably matched planforms. That should give you something to keep busy with for a while.

I am not sure if Arne is able to go on line just at this time,  but I think that when he can, he will give you further assistance [it may be a couple of weeks].