Minimum Width rudder can be built yet remain

Class rules are open on the subject.... go down to a 3mm alloy sheet if you want to...

Rudders have been known to go down to 6% sections but you start to move into the area where exotic materials are needed. It really depends on the chord length of the rudder, a huge long chord length means that you can go down to lower %ages but you might not want a long chord length for other reasons, mainly drag and weight on the helm. I suspect an oppy rudder has less than 6% section but then it is basically square, so it is inefficient for other reasons. 

Most of the time, you don't need much rudder, but I seem to recall that MiniSails sometimes need a lot of steering downwind, as the boom is long and the hull is not keen to be under the rig?
The hull itself is fairly ambivalent about direction of travel, particularly if you succeed in keeping it flat.

I had one many, many years ago, I bought a new sail for it from Great Western Sails, about 10 minutes before the CA started allowing battens.
How about a dagger-box type rudder and pull it up a bit if you feel too much under control?

The Minisail rudder can be very, very heavy off wind as the boat tries to broach if the balance is wrong. Too narrow a blade will simply let the boat spin out, I suspect. However, I've really not figured out what works best. The standard rudder is pretty poor, just a piece of ply.

Originally posted by JimC Fatter sections tend to be preferred on rudders because they stall less easily. The choice of section too is relevant, usually something more forgiving than the rudder. I wouldn't change the area too much away from stock because of the rudder's role in balance and lateral resistance, but having said that the minisail may not have had optimally set up foils out of the box.

IIRC the original MS sails were quite horrible by the time they were a year or 6 old, full, stretchy, often funny colours...
I'd hazard that optimisation of the rudder was somewhat limited.
Also, if the rudder was very big/deep, it would probably have bent the stock all over the place, as this was ludicrously shallow to suit the transom?

Things may have changed over the years, I must have sold mine in the early 80's (?) and it was a bargain boat then, bought to keep sailing while mending something else...
It is one of the few boats I've had that I can't recall the sail number. It was GRP with a wooden, clamp-on sliding seat.