Another technique for driving three rowers in a boat. Three wheels, each connected to a rower, linked by a horizontal bar just like the wheels of a steam train.

One problem. When the three linkage points are lined up in the three o'clock or nine o'clock position the linkage bar can rock up and down. 

To stop this happening I plan to fit a second bar ninety degrees behind the first. Hopefully this would stop it rocking.

Thinking about it further, most of the wheel isn't used. I could cut it away…

Here's the part I came up with. I'll make three of these to test out the principle

They'll fit into a box and the boat fitted to the top like this. To the cutting board!