Minimum Width rudder can be built yet remain

Originally posted by I luv Wight < up on its ear>You see the good guys sailing like that? ( unless it's a scow )The further down the fleet, the more tippy uppy they are.I've made very long, very thin rudders...  seems faster for the faster sailors.

Good guys? Hey it's me we're talking about, when it's windy on it's ear is where I live..

I used to have a nightmare with that RS500 with the rudder not functioning out of skewed up tacks or gybes..

Long and deep could work and I have an old wooden storm foil from a windsurfer that might fit in the stock. I've seen Merlin rudders with an extra trailing tip which I assumed was to counter steerage issues if up on their ears, but then, that wouldn't work would it, I wonder what they're for.

Makes you think the ideal shape might be a scimitar reversed..



Edited by iGRF - 02 Feb 16 at 10:40pm

If you want to lose drag, lose planform area, but as someone else said, respect the ratios of areas between the dagger and rudder.
Rudders are ultimately limited by needing to go to max cl out of tacks or dodgy manoeuvres or keeping control on windy days.
AC foil designer I know said that if you're going below 12% thickness you're better off losing chord (and planform area /WSA and thus friction) whilst keeping a more stall tolerant shape.

You can reach structural limits too. I just built a rudder that can take a tonne of force. 19mm thick, of which ~2mm HM unis in 50mm strips staggered out. Carbon or HD foam shear web. Weighs little more than a kilo.

ou could, if building solid carbon, go to maybe 6 or 8mm thick, but unless it literally is the chord of a windsurf fin, it'll have sh*t stall performance.

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.

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.

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?