The original motor for a Cresta was the
Elmic SPRITE.
These were always an expensive extra, and disappeared from the Keil Kraft Handbook adverts by 1972. Presumably the manufacturer ceased making them - the Cresta was withdrawn shortly afterwards..
For a while the KK Handbook offered another small Japanese electric outboard to replace the Sprite, but that disappeared by 1979, and these small simple add-on motors seem to have practically vanished from the UK modelling scene. If you want one, you will be paying collector's prices from EBay. The only available outboard I can find in the UK is this
'Hobbys' model, which is really too large and heavy for the Cresta. It also works by immersing a small electric motor completely in the water - which is fine on the first outing, and then turns into a heap of rust internally after a few weeks...
There seemed to be no answer to this deficiency - until reader Ian Holdsworth drew my attention to an old Model Maker (December 1957). It showed an ingenious and simple way to make a small outboard from scraps - exactly what EeZeBilding is all about...
I offer Ian's discovery here to share with you all. Click on it to download a PDF. I don't know how well it will work, but give me a little while, and I'll make one myself.....