By using the line feed system that cranes use you can get rid of the componentn that pulls the car back in completely. Thus solving most problems of the straight track selftacker.

Imagine it like this.

Two 360 degree swivel cleats on the beam on either side of the mast say 0.5 mtr away from mast.

Line goes from cleat to pully on car and than to pully on tack of jib, continues by going back to another pully on the car and then proceeds to the other cleat. If you want more purchase then just extra pullies on car and clew.

Now the car does not experience any RESULTING force that pulls it towards the centreline. The position of the car is now complete determined by the set distance between car and clew of the jib AND the way the jib curves up. No fine tuning with purchase ratio etc required; only add purchase when the pull on the sheet is too high for your taste.

Simple effective and cheap.

It is still not as optimal as a curved track becuase you have less control over tension on foot c.q. leech and the curve of the jib sail but it will come close.

Wouter