Or indeed even a horse! Driving one consists of walking behind controlling it with long reins, possibly even while towing a boat. You need the boards permission to do that nowadays. Now I'm not sure where you'd be legally if you were instead leading the horse, after all if leading an animal on the towpath is not allowed that would rather compromise dog walking........?
Back on topic, I looked hard at the motorcycle options, even going so far as to design in a nice long 10' well deck, looked at hoists, scissor lift table, ramps etc. You have to bear in mind that you plus a heavy bike on a ramp resting on one gunwhale is going to make even a well ballasted deep drafted boat tilt alarmingly. In the end the cost and complexity of the engineering didn't justify the limited use so I shelved the idea. (The 10' deck is lovely though)
I'm looking again now at really small 125s - think monkey bike, or maybe wait until lightweight electrics become practical. The idea being to commute back to wherever a larger vehicle is, or just for shopping etc.