Paul Terry wrote:
Tom Anderson writes

Play fair - the boats have rather lower capital costs than the tubes,
since the track's already there.

On the other hand, the "stations" have to go up and down with the tide


Anyone who has been to Venice will know that efficient water-borne
transport is possible (although it is massively subsidised), but the
tiny tidal variance in the lagoon allows for very lightweight landing
stations and very fast and efficient two-crew operation (probably taking
no longer than a tube stop).

The great rise and fall of the Thames necessitates complex pontoon
structures, and I suspect that the UK's HSE would not approve of ACTV
Venice's operating procedures that facilitate three-minute service
intervals and timings of one minute per stop.

Actually operating boat services on tidal rivers is very easy! The
(small) CityCat on the Brisbane river, and (large) Sydney ferries on the
Paramatta River do it all the time.