Battery power has been easing the burden of diesel gensets on one of London’s busiest river crossings
Transport for London (TfL) has replaced its River Thames Woolwich Ferry with two battery diesel hybrid ferries which entered operation earlier this year.
Naval architect LMG Marin joined forces with Remontowa shipyard to make a common offer, which won the open tender. It was a significant project for LMG Marin. While the company has designed battery retrofits for several vessels, this was its first newbuild battery design.
Explaining the details behind the battery hybrid solution for the two new vessels, Ben Woollacott and Dame Vera Lynn, LMG Marin managing director Torbjorn Bringedal says: “TfL knew what it was going for, and it is a very specific route, a very short crossing over the River Thames.”
The engines on TfL’s new ferries will run at a constant low load, with batteries taking dynamic loads in peak shaving
This operational profile helped to define both the shape of the ferries and the way they connect with the shore. The new boats meet London's Low Emission Zone standards because of their diesel-electric hybrid propulsion systems.
“This battery diesel hybrid solution is intended to make the life of the diesel engine perfect,” says Mr Bringedal. Diesel engines, which use low sulphur fuel, run on a constant low load with the batteries taking dynamic loads in peak shaving.
“The diesel engines produce constant power, so the batteries are covering power needed beyond this, such as when the thrusters need to change load. All these peaks are taken by the batteries, so the diesel engines are not affected.”
The advantages of using batteries for peak shaving on the ferry are that they allow the diesel engines to have the best efficiency possible, with the lowest specific fuel consumption. Mr Bringedal adds: “Batteries are suited to a short river crossing. The ferries are basically manoeuvring all the time – there is no transit period, so it is a tough life for a diesel engine if you have a direct mechanical or traditional diesel-electric solution. Here they are protected by the battery system.”
The batteries, which are charged by the diesel generators, also allow the best possible conditions for the exhaust to be cleaned. The diesel engines are equipped with a catalyser and with particle filters on the exhaust. The catalyser takes NOx emissions away and the particle filters take away visual smoke or substances that end up as smoke.
“The ferries are basically manoeuvring all the time – there is no transit period - so it is a tough life for a diesel engine”
“There is hefty exhaust cleaning on this design,” says Mr Bringedal.
Explaining how the design brief was met, he says: “To make the batteries and diesel engines run smoothly, we undertook route study considerations and looked at the operational profile of the vessel. The next step was the safety issue, we took a specific risk analysis approach to make sure the batteries were safely installed and safe to operate. Batteries are still new technology for marine use and class wanted a risk-based design process.”
The equipment package per vessel consists of battery packages provided by Corvus, two diesel generators by Cummins and four thrusters by Hydromaster.
Norwegian Electric Systems (NES) provided the two hybrid electric systems for the new ferries. The NES package consists of ultralight converters forming a DC-grid system with four battery packages, two on each side of the DC-bus for redundancy. In addition, for the main propulsion there are water-cooled, high efficiency permanent magnet motors and four direct driven propellers.
Another striking factor about the ferries is that they are using an automatic mooring system by Mampaey. This consists of a magnetic solution where a large magnet is clamped on to the side of the ferry.
Mr Bringedal says: “You need to have a relatively flat ship side surface and a certain thickness of steel to make sure the magnet attaches well. They lock these on when loading and unloading and shut down the thrusters.
“Normally ships use thrusters to push towards the linkspan to make sure they stay in port, but now they will be kept in by automatic mooring which saves a lot of energy, especially when using this type of connection where the crossings are done so frequently.”
The automatic mooring system will also enhance safety – the magnetic technology makes the vessels more stable to board and alight.
An auto mooring solution is a relatively new application on a ferry and, says Mr Bringedal, is usually used in harbours for bigger ocean-going cargo ships.
The control system to link the ferry to the auto mooring system and the link span was installed and commissioned in January, after which TfL carried out berthing trials. After replacing the existing berthing structures with floating pontoon berths and incorporating the automatic mooring system, the river bed was dredged to accommodate the new ferries at low tide.
As well as bringing energy savings, an important factor for the ferries is strong manoeuvring ability and high thruster redundancy. Mr Bringedal explains there was a focus on having the “smoothest line for the best possible transit conditions with the lowest possible resistance. The shape of the hull is more like a barge where four thrusters are installed, so the focus is on very high manoeuvrability.”
The ferries are manoeuvring for the entire crossing and need no course-keeping stability. “There are four thrusters for manoeuvrability and redundancy – when you have four knots of current you do not want anything to fail in these operations, so a high level of redundancy is a good thing.”
Other benefits include 14% more space for passengers and vehicles – the boats will be able to carry 150 passengers, with 210 m for vehicles across four lanes as well as dedicated cycle spaces. There will also be step-free access.
Ben Woollacott and Dame Vera Lynn
Passenger capacity: 150
Vehicle capacity: 45
Batteries: Corvus Energy
Diesel generators: Cummins
Hybrid electric system: Norwegian Electric Systems
Automatic mooring system: Mampaey