Sadly, I get fascinated by certain topics. I was looking at Krishna's rowing boat and the discussion of how to steer without a rudder. Got me thinking. Here's my contribution:
In reality, rowing boats are steered by lengthening and shortening the stroke of the oars. Taking the 'brief' of achieving steering without a rudder (rather than creating a realistic rowing action) I came up with a simple concept. Rowlocks
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I've got two ideas here. The first part is to create a non-circular motion for the oars (there are many ways to do this). The second is to change the stroke of the oars. That can be done very easily by moving the rowlocks relative to the driving mechanism. Simples!
I have one mechanism that creates the non-circular motion by using and elliptical guide slot and a slotted rotor. The rotor traps the ball in the slot. The second mechanism has the rowlock offset vertically from the rotor and uses a simple ball joint. I have modelled the rowlocks with an radius on them; this could just as easily be a spherical bearing. You need a pin in the rowlock running in a slot in the oar to stop the oar from twisting. I suggest a worm and wheel would be a good way to drive the rotors.
To steer, you simply move the rowlocks left or right as a pair (or keep them still and move the drive mechanism). As the stroke gets shorter, the speed of the oar gets lower too because the oars stay in sync. The stroke on one oar gets longer as the other gets shorter so I don't think you would need too much movement on the rowlocks.
I reckon with a bit more work, you could make the rowlocks rotate too so that the oars would feather on the back stroke. The ellipse could be pretty much any shape (that would not jam up) or the rowlock could be offset vertically to distort the elliptical action and get closer to real rowing.
I don't have the tools to make these mechanisms or any plans to build a row boat in the foreseeable future but if somebody wants to turn the concept into reality I'd be happy to help design the mechanism if help is needed.
It may have been done before but I could find anything quite like this on the net. (Mind you, I get bored very quickly doing 'prior art' searches. Done quite enough of those at work!)
There are some animations on Utube:
https://youtu.be/ndIpSqvaZY0https://youtu.be/nZLZashracMhttps://youtu.be/cFAvfME79QU