Thanks for all of the clarification. I truly appreciate it. I am trying to learn as much, as quickly as I can. 

I have been catching up on my JRA magazine reading, and have been blown away by the wealth of knowledge within those pages.

Wishbone battens and the Aerojunk have captured my imagination, and I think one of those two rigs is the way for me. I feel a lot more confident in my mechanical skills then driving a sewing machine to make a complex sail.

I have more sketches to make,  measurements to take, and pondering ahead of me.

If I can do an Aerorig in the current mast position of my boat, things sure would be swell. The mast would be truly unobtrusive, and I have a hunch that it would positively affect my balance rather than having it shifted forward. No proof, but just a hunch. 

Thanks for all of the fantastic info and for helping me along my junk rig journey!

I see now that in «Principles of Yacht Design», by Larsson, Eliasson and Orych, the authors distinguish between geometric and dynamic CE and CLR.

The geometric CE and CLR is the traditional method, and easy to find by balancing the actual areas on a ruler etc. The dynamic CE and CLR are the real centres of pressures, which generally run around a bit and sit more or less forward of the geometric versions. These are much harder to find. That makes sense to me.

They conclude that to find the correct sail position on a new boat, they recommend using the geometric CE and CLR, and then vary the lead (CE’s distance in front of the CLR). They had set up a little table of recommended amount of lead for the different hull types and rigs.

Arne

Hi Guys,

This thread is running on mixed information and is a bit like running through a mine field. The terms being used can have different interpretations, so it might be safer to define the starting point.

Starting from the bottom, I assume CLR stands for Centre of Lateral Resistance, which is a dynamic point depending on such things as leeway and heel. I can only assume you are talking about Centre of Submerged Area, in an upright configuration. Even in that case when the side elevation is cut out and balanced some will include the area of the rudder, some ignore it and some include one third of the area. As the rudder is normally well aft then the three results can be quite different in longitudinal position. 

Similarly, I assume CE stands for Centre of Effort, is referring to Centre of Area which are certainly not the same thing. The Centre of Effort is also a dynamic position and depends on the wind strength and angle of attack. Importantly it also depends on the camber of the sail, and will be different for a cambered junk sail and for a flat junk sail. We can only assume that in PJR the authors were using their experience with flatish junk sails, so may not be appropriate to use for cambered sails.

My personal attitude is to keep well away form these sums for lead unless you really have to with a home designed and built boat. With Poppy I checked the Centre of Area of the Bermudan rig with full mainsail and 135J Genoa, and compared that with full main and 100J jib and with 2 reefed mail and small/ storm jib, and found that they all fell very close but with the heavy reef position moving forward. Satisfied that the main plus 135J were sensible I selected this for the Centre of Area for the Split rig, but as this is so near the 50% chord line of the lower parallelogram section I now just align this 50% line with the Centre of Area of the normal cruising Bermudan rig. The reason I am happy to do this was that I felt that the relationship between the Centre of Effort and the Centre of Area of the cambered split rig would be similar to or slightly ahead of the CE/ CA relationship of the Bermudan rig. In practice it seems to be the case and has worked well.

Paul is right in saying – Balance ≠ Lead. (It would appear there is no ASCII code for ≠, so some use a != b and other use a < > b)

Cheers,  Slieve.

Thanks for all the help everyone. I am just trying to make sure I understand the decisions being made. I for see this being sort of a major operation on my boat. I feel the better my plan, and the better I understand it, the better the odds that I will have a successful conversion.

I am not entirely opposed to a slight raked mast, but I feel it will add complications to the instillation process. It is an option still on the table.

The aerojunk seems pretty cool, but I feel all the extra hardware and battens will add weight and complicate the build. Maybe I just don't quite understand how it was constructed. I have a nice antique singer 27 knock off I just traded my cheap euro pro for. This thing is awesome, it is lock stitch but has an 8 inch throat and a heavy action. This thing would have no problem sewing leather, or through my fingers, so I hope it will work for the sail. I have found a compatible walking foot for my machine, so hopefully the actual conversion and construction will go smoothly.  

James Hleba wrote:Following this train of thought, since poppy had 30% balance, no lead and got away with it using slot effect,

I don't think it's true that Poppy's sail has no lead. Slieve placed the CE of Poppy's rig in the same place longitudinally as the CE of  her Bermudan rig, which certainly had a substantial lead of CE over CLR.