That’s fantastically helpful, thank you so much!!!
(assuming all this will work on a Cerbo GX with OS Large/Node-Red installed, which I assume it will…)
Then all I have to do is get the imported data into the (new) virtual drive module in Node-RED, and hopefully that’s the job done, it’ll pop up as a device in VRM/remote console, and also appear on the new Boat page… 
I don’t know when I’ll get chance to do this though, the boat is 150 miles away and I’m not due back on it until August – but it does look like there’s now a way forward with no additional hardware except a CANbus cable from the SEVCON (Gen 4) to the Cerbo
Maybe I can even persuade my boatbuilder to try this out on one of the electric boats in his workshop at the moment, he’s been looking for a way to display drive data which doesn’t involve an expensive extra display and hardware… 