I realise whilst we await the furniture-foot-come-motor-mount that left over from the cat (and before that, left over from the quadcopter) I've a U7 motor ready to pin to the boat in much the same way it was prior. You have to be creative when you are prototyping and especially so in order to keep the costs down, which I've a laser focus on nowadays.
Glued to the rear face of the motor is no less than a wardrobe bracket whose main advantage for our purposes is the fact it is available from any DIY store (and more specifically in my case the one within walking distance). It too was destined to hang clothes until one day it realised it had a higher purpose.
If you think this is a bit dodgy, removing these brackets in the past has required a hammer and chisel. What I did previously with it and what we shall do now is to fit a short length of 25mm dowel (or circular timber spar) into the leading edge of the deck with a lengthy screw, recalling the centre-spar used to root the keel is there to cater for it.
In the prototyping trade it's called 'COTS' incidentally, or 'commercial off-the-shelf' and there is nothing more off the shelf than a wardrobe bracket. Online I see that for around £7 you can have one in brass, so long as you're happy with £8 delivery.
Must say I was tempted, as there's nothing more nautical than a brass fitting. The first prototype is destined to last only long enough to prove a point, however, and not to lie on the seabed until such time as James Cameron decides to visit.
Onward and upward, eh Gromit, onward and upward?