Thomas wrote:

In France, the lug rig is called "voile au tiers" not because of the mast balance, but because the slingpoint is fixed at 1/3 of the yard. We need a lot of tension on the luff to raise the yard.

Ah, I must have misheard Sven. Makes sense when I think about it. The masts of his previous design even leaned to the side (illustration, photo).

Graeme wrote:

Did Sven Yrvind rig his sail with a balance that high?

I think all his latest boats have been rigged with 30% balance, but like Thomas said, only where attached to the yard. The one he's working on now has 4 short masts on the centerline, no longer leaning, but still balanced lugs.

Thanks for explaining the effects of 30% balance, I much better understand it now!

I should also mention that Alan of Wave Rover suggested the junk rig to Sven for his previous boat. His answer was:

I have considered the junk rig.
In my case what speaks against it is that I am not familiar with it.

Also the junk sail is tied to the mast, I prefer the balanced lug that is only attached to the mast by the halyard. That makes it is easy to lower the yard, boom and sail and put the bundle on deck. In strong winds that reduces the wind resistance.
Also the junk sail is sheeted from a point aft the sail. That makes it difficult to find a point for the sheet on deck.
The balanced lug do not have that problem. It can be sheeted from a point below the boom.
Then there is the battens. I worry that they may break. True I can have many spare ones, still it is a disadvantage that have to be considered.

https://www.youtube.com/watch?v=A8nv9T2gB3Q

Too bad for us, because he's very innovative and not afraid to experiment (except for the junk rig…).

Sorry if this got a bit off topic with lug sails. I'll let the experts get back to discussing JR mast balance :)

It is relevant Joakim.

Whether or not 1/3 balance is the "optimum" for a balanced lug sail is very much still open to question, but it is, for practical purposes, the "maximum".

It is possible that the balance can be pushed even as high as 35%, but there is a "law of diminishing returns" in relation to most innovations, and in this case over-balance would be disastrous and other factors can intervene, so 1/3 is probably the safe maximum. 

(An over balanced sail will not weathercock when the sheets are released, and in a strong wind it might not be possible to bring the boat up into the wind either - the result then would be a vessel out of control. It occurs to me that if a sail is rigged with balance greater than 1/3, Darwin's concept of "natural selection" may well play a role in the evolution of the modern junk rig! )

Did Sven Yrvind rig his sail with a balance that high? If so, you might have provided a very interesting discussion point as there seems to be an interest among our innovative junk sail designers in increasing balance towards 30% and perhaps beyond.

1/3 balance seems to suit the split junk rig (SJR). 

Any amount of balance makes gybing gentler, and perhaps the more the better. Gybing still needs to be done with care though.

Some people find other advantages in high balance too, but these are discussion points rather than "facts".

The sheeting loads on a high balance sail are less - which means that friction in the sheeting can become an annoyance in very light airs.

Following Slieve McGalliard's research and development of the split junk rig (rather than the feather of Forrest Gump), I gave my sail 1/3 balance and I like it very much.

However, I am not sure that it is "something one should strive for". It is certainly a valid topic for discussion. One of the reasons for studying and proving a range of possible mast balance ratios for the junk rig is that it gives a concomitant range of mast placement positions - convenient when considering the accommodation and bulkhead layout of a proposed junk rig conversion.

Frederik wrote:

That new sailplan for Ingeborg should work just fine Arne. 
Remember the sail of Orion that turned out quite different from your original design?

The lower yard angle resulted in a mast balance of 18-20 %, and a very manageable helm. 

I guess you are right, Frederik. I must see if I have enough sailcloth  -  and energy left for a little sailmaker’s project. However that would be a bit like cooking potatoes; it isn’t difficult, but not exactly exciting either.

It would be more inspiring to make that shown experimental auxiliary rudder. I am very interested in seeing how much steering moment it can deliver, sitting in a free water-flow, compared to the much bigger main rudder, sitting in the dead water behind the keel.

Note; I have no plans of promoting this oar-like construction, in general. It’s just that Ingeborg has such an awkward, 45° transom. In addition, her stern is quite busy already, so there is only just room for that rudder shaft between the sheet’s chain-plate and the aft lantern.

On a normal transom à la Albin Vega or Maxi 77, I would just have fitted the aux rudder to the transom.

Arne

(Full size diagram under Arne's sketches, section 8...)

That new sailplan for Ingeborg should work just fine Arne. 
Remember the sail of Orion that turned out quite different from your original design?

The lower yard angle resulted in a mast balance of 18-20 %, and a very manageable helm. 

Paul,

this topic may well end up running until Christmas, as it is quite ‘wide’.

I just grab a few points as they come to my mind.

Tradition
Things and habits soon develop into traditions, and one soon starts to copy from the past, with only small steps of development. Tradition tends to slow down development of everything, from tools, to sails  ( -  or Lederhosen ). This can be both good and bad, as we know.

Conservatism (a variation of tradition)

People are sceptical to new things. I published an article about my first cambered panel JR in #30 of a JRA Newsletter. After that, there was a roaring silence in JRA for the best part of 10 years (..there were a couple of exceptions, of course...)

Reasons for low mast balance.
In my case it started by copying Hasler’s and McLeod’s rigs. I had to start somewhere. Later, due to preferred mast placement, the sails were forced to be hauled far aft. Since I feared that the mast would badly reduce the performance on port tack, I reduced the mast balance to a minimum. In addition, on Johanna (48sqm), there was a lee helm issue with that boat, so increasing the mast balance would have called for a mizzen. Later findings by Paul Thompson showed that higher mast balance would work just fine.

Size.

On smaller boat, below 1500kg and with sails no bigger than 25sqm, I still think the low-balance sail is the best, as it lets one set the biggest sail on the shortest mast. The 20sqm JR for my Frøken Sørensen was a joy to handle. Mast balance (around 15%?) was never ever thought of, and the handling of the parrels was easy.

Rudder.
I think we in the West have badly over-looked the rudders when designing junkrigs for our boats. Chinese vessels are practically sailing on their rudders.
My Jollenkreuzer, Frøken Sørensen, had an extraordinarily deep and efficient rudder. Thanks to that, I never had the slightest fear that I would lose control. Sometimes the boat heeled until the cb. lost grip, but she was still controllable. Rudders, rudders, rudders! These days I am dreaming up an experiment on Ingeborg...

I let you have a glance at that plan  -  or maybe it’s just a daydream...

Load on battens
As you have found out recently, at 27% mast balance, the battens start to bend the wrong way. This may (possibly) be a limiting factor, although the SJRs seem to work. I dunno...

Arne

(full size diagram on Arne's sketches, section 8-5)