Eventually there's no better way to mount motors than directly on the cross-spars, and I look again at the simplest configuration viz. contra-rotating units at leading and trailing edges.
Then I stand back for a think, and looking at this my mind is filled with dread.
For literally from the get-go, aeroplanes have had issues with asymmetry. The first aircraft ~ the Wright Flyer ~ apparently needed one wing longer than the other to offset the weight of an engine fixed off-centre.
The Flyer though had two propellers, and worse was to come because designers the world over settled on a single propeller for its practicality. This led to an immediate problem, because the airframe wanted to rotate the opposite way as a reaction to the torque. Worse than that, the airscrew added 'swirl' to its efflux which produced unwanted rotation when it struck the tail.
One of the most successful Italian biplanes of WW1 therefore featured one wing that was longer than the other, principally to offset torque. Whilst people actually appear to prefer an element of asymmetry in faces, though, they don't like it in means of transport. The solution to this was to leave the wings an identical length, but rig one at a different angle of attack to the other.
When I look at the set-up in the picture, I therefore see rocks ahead. Should the foremost propeller run clockwise as viewed from the rear, irrespective of torque effect it will rotate the deck in the same direction by force of efflux. The rearmost propeller meanwhile has to run anti-clockwise, which also produces a clockwise bias by way of torque reaction instead.
What this means in the worst case is that the boat may be inclined to pursue a right hand turn that cannot be corrected by differential thrust alone, and which may take an inordinate amount of testing to resolve.
We're back then at Plan A as regards configuration for testing viz. coaxial motors on a common beam, which I've decided to christen the 'power bank'.
While nothing in life is wasted, I offer this afternoon as evidence to the contrary.
