Firstly, if we always sailed in gentle breezes and on a flat sea we would need no devices to steer with whatsoever. We could achieve any heading and hold it by means of sail trim and hull trim alone. Relaxing and super simple...
And even as the wind pipes up and the sea state rises, one can still go upwind perfectly well - again with only sail trim and hull trim.
But try that on a reach or an offwind course and you will yaw wildly. And in a really fresh breeze forget about going offwind without some kind of foil in the water for course correction. It's impossible. You might get going in the desired direction initially but you'll yaw crazily when a wave picks up your stern and tries to throw you around. You will need either a steering oar or a rudder of some kind.
Believe me, I've tried. Have sailed many a mile in a boat with no underwater appendages of any kind and it's a joy on flat water but a crying shame in a breeze... Upwind no prob, downwind lookout!
Steering Oar or Rudder?
My first attempts involved steering oars - keep it simple and straightforward... I fashioned a beautiful and sturdy oar with adequate blade area and hung it off the leeward side well aft. It looked great and felt great. But the first time I went out into the big bay in big wind and turned offwind I had my hands more than full. I went off flying on a broad reach and skipping from wave top to wave top on the smaller waves and surfing on the larger ones, whooping all the while! But my steering oar required two strong arms just to keep from rounding up! And I already need one hand for the mainsheet! It was a blast but made a mockery of my big tiki-sized steering oar! I needed a better solution...
I'd come across references to and photos of so-called quarter rudders so I decided to investigate those. These are used on the Carolinian canoes. Hung over the gunwale on the lee side, they rest on a pivot and are restrained with a line running from the top over to the windward rail. They are tiller operated but their tillers protrude aft rather than forward - the steersman must push on the tiller rather than pull in order to bear off. Here's a picture or two.
|From a Herb Kane drawing|
|From an early drawing (from Pâris (1841)|
And here are some photos of contemporary examples. The rudder is not needed for upwind use. It's barely in the water. But the further offwind the course, the more it must be used. It is pushed down into the water by the helmsman's foot, as much as is needed. (The command to bear off is actually the word for "foot".)
These rudders are not very well faired as underwater foils go, but they're serve well for their intended function.
|More rudder needed|
So I built my own quarter rudder to try. The tiller projects forward of the rudder, Western style, and it is built to allow the rudder to kick up as well, for shallow water. My first design (see the drawing below) actually worked well enough that no modifications were needed. I tell you, this rudder provides complete and painless control even in the breeziest conditions. One note: It does not provide an impetus for turning upwind (it won't function turning that way) but that's not really needed.
|A simple quarter rudder|
When shunting, this rudder is easily unslung from the old stern and brought across to the new stern.
P.S. I would use this again on a new boat, but I might also experiment with a system of dual rudders as shown here: http://starrigging.blogspot.com/p/dual-rudders.html