Yes, David,
our thinking about shifting the CP aft by moving the hinges, and thus max camber point aft, is identical. I have asked Chris to read about my hinged battens in JRA Newsletter 24. I found that my symmetric hinge-camber on Malena added some weather helm, compared to when the same sail was flat. When I made the cambered panel sail, with max camber  about 35% from the luff, it initially produced a lee helm. After pulling the sail aft, the balance was put right again.

Arne

On Chris’ request I digitized a drawing he had made on his flat old junksail, and trial-fitted it to the Red Fox Vision he wanted to buy. First I had to digitize the profile of the boat and her Bermuda rig (BR). The result can be seen below, to the left. Since Chris wanted the mast to go through deck forward of the hatch, I soon found that a plumb mast would not work, so I tried with different aft-raking angles; 1, 2 and 3°. As can be seen, the 2° rake brings the mast top far enough aft to set the sail with the CE about where the CE of the BR sits. I needed to make the mast quite tall to get an acceptable halyard angle.

While I was at it, I (..surprise, surprise...) tested if I could make a Johanna-style sail fit to the same mast, without moving it. The diagram to the right shows a sail, crimped from my AR=1.90 master sail. I deliberately moved the CE of this sail 2.9% of WL aft. Still, there is lots of room for moving this sail forward, if needed.

At first glance, this sail looks wrong, with next to no balance in the sail. However, I think that as long as the mast top is in the right position, all is well: See that thick grey plumb mast line, coming down from the same mast top. This indicates that the balance is next to 9%.
Frankly, I think this would work fine.
See for yourself.

Cheers, Arne

Thank You Annie and David your your helpful replies. Raking the mast seems to be good - I had never thought about its effect on the hinges. It takes the weight out of the throat parrell and thus hinges articulate in lighter winds?? I'm still umming and erring over the Red Fox Vision - you are right Annie - I just want her and should go for it. It is sometimes very hard to explain why a certain boat design is so appealing. Yes the rudders could easily be modified.

I will make a decision soon and then drain the forum for advice.

Many thanks

Chris

Chris, 

I sailed on the first Vision, as she was assembled in the same shed as Tystie was being built in. I went out with David Thomas on the first sailing trial. She reminded me very much of my Sadler 25 Llliutro, on which I had junk rig variants for twelve years. In common with all centreboard and bilgeboard boats, it was difficult to raise or lower the boards when there was side pressure on them, but you learn how to cope with this. I think the Vision will convert as well as any other small modern boat. Weaverbird, with her Sonata hull, also designed by David Thomas, is of the same hull type but with fixed twin keels, and I'm very happy with her performance.

It's true that the further aft the mast can be, the less of a piledriving and pitch-inducing tendency there is, but this is something that a single masted junk has to live with. The way to reduce the effect is with a forward raked mast, so that the sail has its CE where you want it, the upper part of the mast is well forward so that balance area is minimal and hinges will articulate well, yet the heavy lower part of the mast is further aft. 

I for one, am very interested in your new rig for your new boat.  The Red Fox Vision incorporates many of the concepts that I have in SibLim, so I am intrigued.  My own reservation with your present concept is your 'slightly bendy battens'.  IMHO, battens should either not bend at all, or bend in a controlled manner by the use of some sort of hinge mechanism.  'Slightly bendy' means that you will have a flat sail in light airs - just when you need the most camber, and highly-cambered sails when it's blowing hard - just when you need a flat sail.

Pricey for a small boat?  So what?  If you like the boat and have the money, that's all that counts.  Why worry about the resale value?  It may never happen and if you have to lose some money, well, can you put a price on all the pleasure and satisfaction that a boat you enjoy gives to you?

The location of the mast depends on your style of junk rig, the amount of balance on the sail and the rake of the mast.  A good start is to go to Members' Area/Directories/Member' Boats and search, for example for boats of 2 -4 tons.  Here you should find lots of boats of similar size to your own and you can see where their rigs are placed.

BTW, I should very much appreciate seeing close-up photos of your bilgeboard arrangements.  I have a copy of the diagram, but some photos - and comments as to ease of raising and lowering - would be very much appreciated.  Maybe you would put some in an album?  Thank you.