I came across these pictures while looking for something else
This was a little trial boat made of thin styrene - probably .020
It used a Twin-turbo radio unit which was intended for blimps and has 2 channels each with Forwards, backwards and off on two sticks,
It was powered with 3x 50mah sanyos ( a standard flight pack) and worked reasonably well except that I never made any paddle covers so the electrics got considerably splashed!
Motors were two similar flat mabuchis from Walkman tape drives wired to the motor outputs of the T/T
She was about 5 inches long, and would manoeuvre happily in a pint measuring jug
Now sadly scrapped - but the concept could revive as I was given a contra-rotating toy heli for Christmas which did not make it to the evening before a rotor broke!
andrew