What sort of routes are you suggesting? I'd like to see more use of our waterways to take traffic off the roads but there needs to be demand for it. Canals are fairly unsuitable for commuting unless you're happy getting to or from work at 4mph.
Ok, canals were a bad example. Rivers though we have a lot of.
Gravesend to London was trialled by Thames Clipper. I believe a bit more work there and a few more piers in London would improve commuting into Canary Wharf by ferry and possibly central London.
Southampton to Portsmouth. Cardiff to Weston Super Mare/Bristol. Manchester Clipper using the River Irwell from Media City to Victoria (potential to extend to Eccles if the locks don't take too long to go through). Newcastle could do with something on the River Tyne. Perhaps Glasgow on the Clyde (from Erskine to Glasgow). Just for a few examples. Lots of potentially decent services. Even more if we went down the route of 'bays' to keep the water level high enough.
10/15 years ago there were serious proposals for a Fife (Kirkcaldy) - Edinburgh (Leith/Newhaven) ferry/hovercraft service. Apparently successful trials were undertaken but the service never started. Fresh propsals were put forward a few years later - again not resulting in a regular service. There is significant commuting from Fife to Edinburgh by rail and road both of which involve, for many, a lengthy detour via the bridges.
I think this would be a fantastic proposal to go forward. Transport Scotland says though any potential ferry has to be a commercial venture from start to finish and they will not support it.
Leeds have a ferry service which runs near the south exist of Leeds station to Leeds dock 7am to 7pm weekday and 10am to 6pm .it use to be free but now £1 a single .
There Is the Tyne ferry also Mersey ferry
Tyne Ferry is more based on linking one side of the river to the other and not necessarily commuter or tourist flows. Mersey Ferries has the commuter service but it isn't well used for some reason (Strange given the amount of full buses which go through the tunnels)
I find boats are very slow and inefficient. Dwell times at piers seem to run in the region of several minutes, and the services that do run never seem that frequent.
I will however say the boat in Vancouver (SeaBus) seems the most efficient I’ve used, with customers boarding one side and alighting the other through several automatic doors. Not very frequent still however.
Thames Clipper can spend around 30 seconds on each pier. It all depends on the speed of the boarding/alighting and how efficient the crew are at their jobs.
Some boats are slow but purely as an example, the Red Jet Catamarans can go 44mph in service (According to Wiki). The Thames Clippers can go in the region of 25-30mph. It's not fast but it's also not slow either.
Fife to Edinburgh wouldn't be quicker by ferry, though, not by the time you've got off the ferry down by Ocean Terminal and trundled up Leith Walk on a bus- it's 25-30 minutes from Leith to Waverley Steps alone.
You would be attracting passengers who work the other side of the city or you can go down the route of connecting bus services to get people further into the city.