The channel tunnel for narrowboats.
Brought to you by my brain on REM sleep. The best bit is that it was mostly there to support the main plot point of "man paddles kayak through tunnel, authorities unamused"
Can't stop thinking about the utterly ludicrous engineering you'd need to do in order to make this work (especially if trying to keep the rest of the tech in line with a period where barges & narowboats were still in use as bulk haulage.)
Is it tunneled out perfectly level the whole way, in order to just have a series of locks at the entrance and exit, or do you have locks at points in the tunnel?
How do the boats get from one end to the other? Self propulsion, or do you have them towed along by a system of chains that they hook to and unhook from as needed? ...Oh my god, electric boats using a system like trolleybuses!
