"What would happen if you alternated the position of the masts so that the mast was always windward on one of the sails?"

Most of the pictures in the SWD page show the sails rigged on opposite sides.

https://www.clcboats.com/shop/boats/wooden-sailboat-kits/southwester-dory.html 

You'd think that the difference between the "good tack" and "bad tack" of a balanced lug sail would be significant but, in practice, it doesn't seem to make much difference in either speed or closewindedness.  Even on the "good tack", the sail stands close enough to the mast that there will be turbulence around it to disturb the smooth flow of air on the windward side of the sail, and in the end the loss is about the same.  John Harris points this out in his excellent blog post on this:

Lug Rigs for Small Sailboats (clcboats.com)

For reasons I can't explain, I usually set the balanced lug on my Passagemaker Dinghy on the starboard side of the mast, though it is rigged so it'll go either way.  Seems to look better to me, maybe due to being blind in my left eye, though that might be true for anybody with a strongly dominant right eye.  Sometimes, if it looks like I'll be spending a lot more time on starboard tack (maybe taking longs and shorts going upwind for a long stretch), I'll set the sail on the port side of the mast so that the long tacks will be the "good" tack.  However, I'm not kidding myself--this is mostly because it somehow "looks" better.

What might make a difference, over time, is the chaffing of the sail where it bears against the mast on the bad tack.  So far, however, I've not observed any difference that way.  Maybe on a long ocean passage in the trade winds, but that's not what we're going to be doing in these boats.  <;-)

.....Michael

Ha, I knew Michael would have something logical and experience-y to say! Here’s what I was thinking…

I’ll alter your terminology to move the yard/boom/sail to either side of the mast, rather than move the mast around the sail. My feeble mind isn’t flexible enough ;-)

Traditionally the balanced lug was set to port of mast. This makes the starboard tack the “clean” and supposedly better, tack. The vessel on its starboard tack is the Stand On Vessel. If that is your better tack you gain an advantage. I’ve also seen most mizzens set to opposite side. I think the theory is one sail was always on a clean tack.

The “dirty tack” has the sail deformed by the mast but in my experience there is no discernible difference between clean and dirty tacks. In fact, for a while the “dirty tack” was my better tack. Could point much higher and was noticeably faster. I think what was happening is the mast created a false luff and allowed the sail to take its designed shape. It turns out my rig was not set up properly. My outhalls on yard and boom were way too tight, flattening the sail, and my yard and boom pulled away from the mast making an inefficient foil (clean tack).  Things improved when I got my luff really tight, improved again when outhalls were eased and improved a great deal when I got my yard and boom cinched tight to the boom (but still able to rotate). My takeaway lesson is when you’re performing the same on both tacks you’re probably pretty well rigged.

The Goat Island Skiff folks at Storer Boats race the bejebus out of them and freely share info. Look up their page for really great info on setting up a lug rig. One of the things I remember is that for every inch your boom pulls away from the mast you lose a degree of windward performance.

Bottom line, formulated by folks who really track this stuff, is that for a properly set up rig there isn’t a distinct advantage to either the clean or dirty tack. So, set it up the way it works for you. There won’t be a problem tacking. On a dead run you’d probably want the sail leeward of the mast. It would be easier to douse not having it pinned against the mast. And as Gramps says, less chafe.

Cheers, ev,
(Northeaster Dory, balance lug with yawl retrofit.)