Progress so far. 3 coats yellow enamel on the hull, leftover from my full size boat projects, 2 coats matt varnish on topsides and unsure about adding more yellow, or a different colour? Or none. I find that sometimes the hardest bit of a project is choosing a colour scheme to suit the model unless it is a scale ship/boat/vessel where the colour scheme is a definate. I stumbled into difficulties with this as well, when vessels had different colour schemes throughout their careers.
Anyway, back to the little cruiser, I tested it earlier in the bath, floats pretty much on the chine line, its pretty light. Next was to try motor, speed one, moves ok, quite slow though, next speed, slightly better, tried next speeds till I got to speed 5 (which with the original wltoys l939 is about 15mph) it was slower than I had hoped but still what I would call brisk, certainly not at planing speed but not too far away, maybe a prop fettle, its a bit basic looking. I restricted myself a bit for prop choice by making the propshaft angle as shallow as I could get with that prop. Could always fabricate a nice brass x type racing prop at some point. Will try it in open water soon. I would say that overall, the car motor, battery,receiver board, transmitter and servo are amazing value as a radio for small boat projects. I imagine it would power a battleship or similar of about 24 inches. I think it would go fast in my next project, an even smaller build. The cruiser is pretty wide really. Something narrower should be faster. I would say that this setup is the cheapest way of radio controlling a model boat.
I might manage to design a smaller boat to use this gear, it looked lost in even the 23cm cruiser. A smaller one is next.