As David says, CLR, CoA, CoE etc is a minefield, but I don't see why you should worry about such mythical things.

If you are converting a boat of known behaviour and performance with a conventional rig then use that information to find the CoA for your junk rig. For the SJR and with a Bermudian rigged boat with reasonable balanced performance then I just place an approximate CoA for the SJR in the same longitudinal place. My approx CoA is simply the 50% chord of Jib luff to Main leech. 

So far that has not let me down and has produced well behaved boats.

Cheers, Slieve.

Thomas,

Deciding on the amount of lead is somewhere between an inexact science and a black art; I wouldn’t try to tie it down too closely, especially on a long keeled boat where the actual CLR migrates quite a lot fore and aft in different conditions. I think that a wise strategy might be to go for 16% lead with 25% sail balance - knowing that it’s then going to be possible to set the sail a bit further aft if there’s lee helm in light going. I think that 50 sq m is enough area for the BCC 28, and as I said before, I’d go for a high AR, that should be limited only by the height of mast that you are able to get. A high AR on a short-ended boat like this results in less chance of sheet foul-ups, as well as giving lighter spars aloft and lower loads on the running lines.

Anonymous wrote:

Thomas

Two things:

·        A single sail JR is much more powerful for its area than a 3-sail gaff (or Bermuda ) rig. A 50sqm JR would be plenty for that vessel.

·        A fully long-keeled vessel like this needs the highest lead to get a light helm. I bet that many of the helmsmen did get a good exercise  -  or they added a handy-billy to their tiller. I suggest that you aim for 16% lead  -  or are prepared for that handy-billy…

To achieve 16% lead, I suggest:

·        Keep the sail shape with AR near 1.90, yard angle at 60deg and mast balance of 25% (which lets you move the sail forward or aft, a little).

·        Downscale the sail to 50sqm.

·        Move the sail with its mast forward until that lead is achieved, or at least 14%.

Hopefully, the mast will not end up forward of the boat.

Sorry, I am without drawing tools here.

Cheers,
Arne

Ah, that makes sense. My thought process was that moving the CE closer to the CLR would make a more balanced rig, when its actually the opposite. Is this purely because of the fact the CLR moves forward when the boat is heeled? Or is there something else I'm missing? 

Most of the other boats I'm interested in (pacific seacraft 34/37, Valiant 32, caliber 35) have fin keels and skeg hung rudders. Would you still recommend aiming for a CE 4-6% aft of the BR CE for those with a 60 degree yard + 25% balance setup?

Thank you, Slieve. I did some more reading on your SJR and am very impressed. Although I'm a bit hesitant to add more complexity for increased preformance when, from what I've read, I think I'll be more than satisfied with the preformance of one of Arne's sailplans with cambered panels.

I did a rough sketch of a rig on a BCC28, one of the hulls I'm strongly considering. The CE is tough to compute with the multitude of different headsail options on a cutter. Is there a "proper" way to do that? I drew it with the new CE 10% forward of the CLR. 

Thomas wrote:

Thank you Arne and David for the insight.

I was looking at Le Forestier's designs and the 10.5m has large 50sqm single masted rig. The idea of a running tack parrel seems like it would make sense, and the extra control line wouldn't be an issue with the one sail. That and the forward raked mast to get the CG further forward seems like it would help. 

Is a cambered sail possible with a forward raked mast? 

Thomas

Yes, camber will work.

Arne