This new rig is something which evolved because I felt that existing double luff rigs   were unable to be hoisted and lowered in the normal way . After much (mainly Internet) research and a few experiments with models I decided that a 50% double surfaced sail with twin battens at each station was a good starting point . The battens have an inbuilt kink at the luff end , crossing over about 150mm from the mast so that when tensioned up they force the sides of the sail out into a (hopefully ) aerodynamic shape .

Here is a shot taken looking up inside the sail , early batten set-up and no luff tension applied , below is how it looks from the outside .

This sail is like nothing I have used before , it seems to combine very high lift with low drag even in an overpowered state ( most of the time for me ) with the top of the sail twisting off into pretty much a streamline and all the drive coming from the bottom of the sail , this is giving huge speed though height to windward is still a bit lacking . Much more experimentation is needed on profiles and batten shapes and stiffness .

The mast is , as mentioned earlier , the second attempt , it is a very light carbon spar with the profile of the leading 5% of an NACA10% section . Probably not the most efficient available but very forgiving for stalling . The 5% bit was chosen as it gave a section roughly the right size that it should bend a bit but be strong enough not to need diamonds or uppers to support the spinnaker .

Huge thanks to Brett Scott of Scott Sails who put in  a lot of work to initially make the sail then change it several times to suit the whims of the owner , many thanks also to the aerodynamic web sites out there which provided heaps of information in a digestable fashion . In particular the site of Tom Speer www.tspeer.com , a wonderful resource for anyone trying to understand sails and wingmasts .