Scott,

Your newest rig looks better in my eyes. I notice that you have drawn in a very short halyard drift, as seen on some western lugs. I suggest you make the mast 40-60cm taller. This both reduces the wrenching forces as the sail is squared out, and also gives you freedom to shift the whole sail forward or aft, to get steering balance perfect. This special ability  of the JR saved me on my present boat, Ingeborg: I had underestimated the need for lead, but by later shifting the sail forward of the initially designed position, the steering became good.

On a fin-keel boat with a big rudder on the stern, it is hard to get it wrong. The rudder, sitting far away from the turning axis, and in un-disturbed water, can handle most balance issues. I have had three boats with similar keel-rudder configuration. With the sail’s CE placed at, or just a bit aft of the leading edge of the fin keel/cb, the boat will most probably balance nicely when close-hauled. As one bears away onto a reach or run, or if the boat is heeled well over, weather helm will increase, and there will be more and more need for a rudder to stay on course.

A long-keeled boat is much trickier to get the lead right on, for two reasons:

·         The actual centre of pressure, CP, sits quite far forward of the geometrical CLR, so the lead should be closer to 14-17% (not counting the rudder into the CLR).

·         The rudder itself is often sitting at the trailing edge of the long keel, where the water flow has been slowed down a lot, so the rudder is much less efficient than a freestanding rudder of the same area.

One more thing: A boat with a free-standing rudder and no skeg in front of it, is likely to be directionally unstable. No big deal  -   my last boat, Frøken Sørensen was like that. I solved it by adding a simple tiller lock/brake on it. This freed both hands to let me handle the sheets or whatever, and still stay roughly on the course.

Good luck!
Arne

David Tyler and David Webb,

Can you please confirm that I am following your advice properly?

I have an extremely shallow hull (10" draft on the specs). Because of this I should ignore everything except the rectangular shape of the keel to determine the CLR and then set the CE of the single junk sail at 9% of the LWL forward of the CLR I determined.

As you might imagine I get very different results using just the keel rectangle vs. using the entire underwater profile from the drawing.

I attached a screenshot of my current 'maybe' idea in case anyone is interested.

Thanks again,

Scott.

Hi,

generally the rudder is not included in CLR calculations. If included then the rudder will need to develop some force to balance the rig, that is to say it will create weather helm. 

David.

Thank you Arne and David for the feedback.

I am working on redrawing something closer to 20 or at most 22 sqm. My boat is significantly lighter than Weaverbird. I probably should not need any more sail than that. Point taken. 

As some others have done recently I am planning to build a completely modular sail where the panels are never sewn together. I would like to have pockets or webbing loops or something similar to rig the sail to the battens, yard, and boom. I will consider adding some amount of shape to the panels when I get that far.

I would like to have a vertical leach or maybe even one that has the upper battens very slightly further aft. From the little bit I have messed around with my Puddle Duck rig I understand why this may be important. I would like to have nice easy tacking without the sheets getting hung up.

I am a little stuck on the sail as far as aspect ratio and location. I thought it would be better to go back to following the order in PJR and get an idea of the hull's CLR first.

It seems like QCAD does not provide any way to mark the centroid of a polygon so I did the math myself following what Wikipedia told me. If anyone has a moment to check the image I am attaching I would appreciate it. It seems my 'eyeball' guess is consistently wrong regarding CLR locations on a hull. Does this drawing look something close to correct?

Thanks again for the interest.

Scott.

The S2 6.7 is a little smaller than Weaverbird. I have a 22 sq m sail and that is quite enough. 28 sq m would be enormous and way OTT. Junk rigged boats sail downwind faster than bermudan boats because we deploy our area more efficiently - a spinnaker is really a very inefficient sail, area for area. I hope you'll rethink the area.

"Windward performance is not really of much interest to me." It should be. I don't mean world-beating performance, there's no need for that, but I think you'd be disappointed with a flat sail, for lake sailing. As it's actually easier to make a sail panel-by-panel than the old flat sail method of sewing the whole sail together at once, you might just as well put in a little bit of shape while you're at it.