When it was announced in November 2014 that Sydney was getting six new Inner Harbour ferries, expectations were raised that they would be "some of the fastest on Sydney Harbour", operating on Inner Harbour routes from Watsons Bay to Cockatoo Island.
Unfortunately, fast ferries don't always work well in urban transit systems.
As observed astutely by Kamen and Barry (2006):
"Wheels on steel rails or smooth concrete ... produce negligible resistance compared to the frictional and wavemaking effects of a hull in water. And land vehicles enjoy essentially 100% propulsive efficiency between driveline and useful thrust. Public land vehicles also benefit from an economy of scale: A single operator can drive a train that moves well over a thousand commuters, or a bendy bus or multi-car streetcar holding a hundred or more passengers."
Frictional resistance of a vessel hull in water is significant. As Kamen and Barry noted, "propulsion power is roughly proportional to speed cubed, and most costs are therefore also proportionate to speed cubed or at least squared."
This is why Sydney Ferries' SuperCats, operating at speeds of up to 26 knots to Rose Bay and Watsons Bay, need to be refuelled daily. The more sedate First Fleeters, with a maximum speed of 12 knots, only refuel once a week.
Fuel and maintenance costs are not the only issues. Australian Maritime Safety Authority (AMSA) standards are more demanding for a ferry operator when a vessel's propulsion power exceeds 750 kW. Vessels in this category must be driven by a Marine Engineer Driver (MED) Grade 1. Most Sydney Ferry masters are not qualified at this level.
For this reason, I'm guessing that the new Inner Harbour ferries, due to enter service later in 2016, will have a propulsion power of 749 kW. They will then only require an MED 2 at the controls, but reach a modest speed of 20 knots at full throttle. That will be about the limit, given the superstructure and passenger capacity proposed for the new vessels.
There's nothing wrong with 20 knots for most of the Inner Harbour. The geography of Sydney means a slow ferry to Cremorne Point, Kurraba Point or Balmain East competes quite effectively with land transport.
The real problem lies with Watsons Bay and Rose Bay. Even with improvements in passenger loading, the new vessels will not be able to keep the current Eastern Suburbs timetable if their maximum speed is 20 knots.
Why not change the timetable then?
Timetables are constrained by mathematics as much as propulsion systems. It takes about 11 minutes for a SuperCat travelling at up to 26 knots in open water to make the 6.2 km journey from Rose Bay to Circular Quay. After adding time for passenger loading and unloading, the round trip can be completed in 30 minutes. That's tight, but one SuperCat can operate a 30 minute interval service to Rose Bay. With two SuperCats, it could be a 15 minute interval.
If the current Watsons Bay wharf was upgraded to a better design, a round trip to WB, with a stop at Rose Bay in both directions, could be completed in 60 minutes with a speed of 26 knots in open water. This would require two vessels with a 30 minute interval.
This neat scenario falls apart if a slower, 20 knot vessel was to replace the SuperCats. The 11 minutes from Rose Bay to Circular Quay goes up to 13 minutes. Rose Bay round trip goes from 30 to 34 minutes; Watsons Bay round trip goes from 60 to 68 minutes. Result misery.
The 20 knot vessel option does not work for the Eastern Suburbs because, with clockface 30 minute headways, the slower speed will lead to long layovers at either end and an extra vessel added to the runnings: a very wasteful outcome all round.
So what's to be done about the Eastern Suburbs? My guess is that the SuperCats will continue operating on Eastern Suburbs runs for some time - and the new Inner Harbour ferries will probably not venture to either Rose Bay or Watsons Bay.
What this means for Sydney's ferry fleet strategy is unclear. The First Fleet Ferries have plenty of life left in them. With nine First Fleeters and six new Inner Harbour boats to come into service over the next 18 months, there is capacity to expand the Inner Harbour network. This comes at a cost, of course. With the new Inner Harbour ferries, plus the recently announced four new Parramatta River ferries, the complexity of Sydney's diverse ferry fleet could be greater than ever.
Ferry passengers of Sydney must wait with baited breath to see what transpires.
Kamen, P. & Barry, C. (2006). Urban Passenger-Only Ferry Systems: Issues, Opportunities and Technologies. In R. Delpizzo (Ed.), Sustainability in the Maritime Industry: A Collection of Relevant Papers. New York: Society of Naval Architects and Marine Engineers.