Richard J. wrote:

Brimstone wrote:
Richard J. wrote:
Brimstone wrote:
Mrs Redboots wrote:
Richard J. wrote to uk.transport.london on Fri, 25 Mar 2005:


But IIRC the tidal rise and fall in Sydney is quite small. In
London it can be more than 7 metres.

Given that for centuries the river provided almost the *only*
public transport available in London, I rather suspect that this
is a problem which has been overcome in the past, and can be
again.

Is it even a problem since boats are loading and unloading now?

Yes, but carrying relatively few passengers. This discussion is
about using the river for mass transit - many thousands of
passengers per
hour. In comparison with trains, boats have very long dwell times,
partly because berthing at a pier takes longer than arriving at a
platform, and partly because it takes longer to embark/disembark.

Surely that depends on the design of the vessel and of the pier?

A Tube train has up to 32 door openings to access 2.5 metres of train
width. If you built a boat that narrow it would be unstable, so you
have to build it wider, but you can't then fit enough doors to empty
that width of boat as quickly as a train.

Yes, obviously it takes longer to load and unload than a train - but at
most locations a single pier would be sufficient. Only major
destinations like Canary Wharf would require really long stops.

And remember, the doors on boats can be a lot wider than those on a
train.

So to get the capacity you'd have to provide many more pier berths
than at present, equivalent to having, say, 8 platforms at every
tube stop. Having 7-metre tides and strong currents means that
berthing will be even slower and it's more difficult to design
such a pier for large numbers of people.

I accept that a different design would be needed for commuter
(compared to the current leisure) levels of traffic but why would
they be more difficult to design?

To accommodate tides of 7 metres or more, you would need ramps totalling
90 - 100 metres long (to limit maximum gradient to the DfT guideline
maximum of 1 in 12), and sufficient of them to cope with large passenger
flows. It's not impossible, but it's a significant constraint on the
design, and may limit potential capacity just because the piers would
take up so much room.

So obviously you just ignore the DfT guideline maximum! 'Tis not a
problem when your vehicles are crew operated...