This started as a comment in response to comments after yesterday's post, but I've decided to put it in its own post.
The amount of leverage is determined solely by the distance of the handle from the axis of rotation of the rudder. Imagine a straight line extending up from the rudder post, and draw a line at right angles to it such that it hits the handle. (This second line will be approximately along the tiller arm.) In terms purely of leverage, i.e. how easy or difficult it is to push the rudder round, the shape of the metalwork connecting the handle to the rudder makes no difference. So, just because the swan neck takes the tiller arm "backwards" a little before coming forward to the handle, that in itself doesn't add more leverage. One way to see this is to imagine the bends of the swan neck filled in with solid metal - this imaginary metal can extend backwards, forwards, up or down - even left and right - as much as you like. The swan neck is still there, it's just got some extra metal attached. Now you could make the rigid structure connecting rudder and handle any shape you like, and then, if you wish, remove the "imaginary" metal. The ease or difficulty of pushing the rudder depends only on the distance of the handle from the axis of rotation.
Having written the above, I think I've just realised the importance of the shape. If the handle is connected to the rudder post in a straight line, which, in my treatment of the problem above is entirely feasible, then the small word "rigid" becomes especially important. Trying to move this would put a lot of force on the rudder post in a different direction to its normal rotation, and the straight connection would try to flex. If it doesn't flex, and if the rudder bearings can cope with the strain, than it would work, but it would obviously be impractical. As far as I can tell, the shape which would introduce the least unwanted stresses on the rudder bearings is a simple right angle - as on Ross Barlow. But if the shape has curves and a bit of springiness then it will absorb shocks better. Perhaps this is a good reason for the curves and the swan neckiness.
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