Two landmark ferry projects have recently come to fruition – Transport of London’s battery hybrid ferries and the first ferry to operate on LNG in the Mediterranean. LMG Marin opens up on the innovations behind the design of these ferries
Transport for London (TfL) has replaced its River Thames Woolwich Ferry with two battery diesel hybrid ferries due to go into operation at the start of 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, because while the company has designed battery retrofit vessels, this is 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 said “TfL knew what it was going for, and it is a very specific route, a very short crossing over the River Thames.” He said that this aspect lay behind the physical shape and interfaces of the ferries.
“This battery diesel hybrid solution is intended to make the life of the diesel engine perfect,” said 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 are producing 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.”
Battery boost for river crossing
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 added “Batteries are suited to a short river crossing as this is such a short connection. 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, so I believe this is an excellent solution.”
The batteries also allow the best possible conditions for the exhaust to be cleaned. “There is hefty exhaust cleaning on this design,” said Mr Bringedal. 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 batteries are charged by the generators.
Explaining how the design brief was met, Mr Bringedal said “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 new boats meet London's Low Emission Zone standards because of their diesel-electric hybrid propulsion systems.
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.
Automatic mooring heightens energy saving
Another striking factor about the ferries is that they are using an automatic mooring system by Mampaey, which will also save a lot of energy. This consists of a magnetic solution where a large magnet is clamped on to the side of the ferry. Mr Bringedal said “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, said Mr Bringedal, is usually used in harbours for bigger ocean-going cargo ships.
At time of writing (January), the control system to link the ferry to the auto mooring system and the link span (bridge) was being installed and commissioned. TfL said that once this was done, it will carry out berthing trials. It said that after replacing the existing berthing structures with floating pontoon berths and incorporating the automatic mooring system, the river bed will be dredged to accommodate the new ferries at low tide.
As well as being energy saving, an important factor for the ferries is strong manoeuvring ability and high thruster redundancy. Mr Bringedal said 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 manouvrability 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.
The first LNG-powered ferry on the Mediterranean has been delivered – Italian ferry operator Caronte & Tourist has taken delivery of a 133-m long double-ended ferry from Sefine shipyard.
The 8,055-gt ferry, named Elio, has capacity for 290 cars on two vehicle decks and 1,500 passengers.
The propulsion is based on a gas-electric system using three dual-fuel engines.
LMG Marin designed the ferry. Mr Bringedal said “Caronte & Tourist contacted us in 2013. They were planning a newbuild and have several older Norwegian ferries in operation. They asked us to make an initial design. We worked with them to come up with the optimal design and asked 13 shipyards to bid before Sefine was chosen.”
He said that Turkey-based Sefine was selected due to a combination of price and experience. “Sefine has already delivered Norwegian ferries so has a track record and there is no doubt that Turkish shipyards are very price competitive compared to other European yards.”
Mr Bringedal said the ferry was the largest double-ender that LMG Marin had ever designed. While the ferry is a dual-fuel LNG ferry, the original shipbuilding contract was for it to be a diesel-powered vessel with the option to install all LNG-related equipment. But once construction started it was decided to build a fully-operational LNG dual-fuelled ferry.
It uses three main Wartsila 6L34DF engines of 3,000 kW each and two Rolls Royce Azipull 100 CP thrusters of 2,500 kW each, which will allow a top speed of more than 18 knots. MAN Cryo has delivered the LNG supply system, which consists of a 150-m3 vacuum-insulated storage C-type tank with auxiliary equipment including an LNG vaporiser, pressure build-up unit, bunker station and heat exchanger.
There is an engineroom at each end of the ferry and a central LNG tank. A gas-electric solution is used, with thrusters at each end of the ferry.
Sefine Business development manager Selçuk Bakanoðlu explained the challenges and considerations for Sefine when it came to the LNG dual-fuel system. “There was a lot of piping work and safety requirements, and these all affected the building process. Production and mounting of pipes, valves and all equipment belonging to the LNG system needed careful work and supervision… With the qualified engineering and management team of Sefine Shipyard and our suppliers’ site team we took care of all these processes.”
Mr Bakanoðlu pointed out that other energy saving solution included the hull form, which gives a highly efficient ratio for fuel consumption, and the air conditioning system which uses waste heat.
Manouevring key requirement
A major consideration for the ferry is not just using LNG, but also operational flexibility.
This ship will primarily operate in the Strait of Messina, linking Sicily to the Italian mainland. Mr Bakanoðlu said that two 400-kW powered Veth Compact Jets CJ-1000Vs “give high performance against strong currents of Messina Strait and high ability for manoeuvring”.
Mr Bringedal added “The strait is almost like a river with a very strong side current, so the owner was nervous about the thruster capability and redundancy of the ship, especially when manoeuvring, so we made sure the main thrusters were free pulling in 360° – so not only very efficient in transit but also in manoeuvring, combined with no skeg to drag the vessel sideways.”
A redundant manoeuvring system was installed consisting of a standby thruster solution that does not produce extra drag. Mr Bringedal explained “We did not use normal tunnel thrusters as they require skegs to be mounted in, instead we installed pump jets in the bottom of the hull without skegs, with one at each end of the ferry. These act as redundancy and are quite a unique solution. They are usually used on river vessels that cannot be too deep. They are not extremely efficient, which is why tunnel thrusters are usually used in oceangoing vessels.
“But we calculated that we were getting about same amount of drag on a skeg as that which was being produced by the tunnel thruster, so there was zero gain in using a tunnel thruster.”
He said the vessel could experience up to six knots of side current in extreme cases, whereby a large current could grab onto the hull and drift it.
Speaking about the redundancy of the vessel, Mr Bakanoðlu said Elio can use the propulsion systems individually. “During a voyage, the captain can use one or both forms of the propulsion, including the Veth Compact Jets. To provide this ability, Elio is equipped with two main switchboards.”
The vessel has been built to class B, the highest class possible except for international voyages, as the vessel will travel to remote islands. “This is why it has enclosed part of the upper car deck on one end, to comply with stricter rules for bow height and stability,” said Mr Bringedal.
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
Length: 133 m
Capacity: 1,500 passengers and 290 cars
Gross tonnage: 8,055 gt
Engines: Wartsila 6L34DF
Thrusters: Rolls Royce Azipull 100 CP thrusters
LNG supply system: MAN Cryo
Water jets: Veth Compact