Scottish ferry operator CalMac Ferries will be introducing a new ropax vessel in September that is particularly innovative when it comes to propulsion and the design of its bow.
Scottish ferry operator CalMac Ferries will be introducing a new ropax vessel in September that is particularly innovative when it comes to propulsion and the design of its bow.
The 116m long Loch Seaforth, which will be capable of operating 24 hours a day and have capacity for up to 700 passengers and 143 cars or 20 commercial vessels, will operate on the west coast of Scotland, between Stornoway and Ullapool.
Martin Dorchester, chief executive of CalMac Ferries, told Passenger Ship Technology: “The decision to commission Loch Seaforth arose out of the need to replace a freight ship, Muirneag, which operated overnight between Stornoway and Ullapool, and which was nearing the end of its working life. An appraisal into the options by the Scottish Government concluded that the departure of Muirneag presented an opportunity
to replace the passenger roro ship
Isle of Lewis, which ran on that same route, with a single ship which would do both jobs.”
He added: “The biggest difference will be to customer comfort. The new design and modern engines also provide scope for operational efficiencies. The arrival of a new ship is an exciting time for any operator. In addition to being a welcome investment in new tonnage we are hopeful that the new ship will attract more passengers to the route and to the Western Isles, as evidence suggests that a new ship can be a positive catalyst in increasing traffic.”
The responsibility for procuring and managing the build of ships for the Caledonian MacBrayne fleet rests with Caledonian Maritime Assets (CMAL), which is wholly owned by the Scottish Government. In June 2012 CMAL commissioned Flensburger Schiffbau-Gesellschaft (FSG) to build the new £41.8 million (US$70.9 million) ferry. Financing is being provided by Lloyds Bank’s corporate asset finance team. CMAL will charter the vessel to CalMac Ferries.
Loch Seaforth has close to 1,500 tonnes of deadweight, which means that its capacity is almost three times greater than that of Isle of Lewis. While the dimensions of the new vessel have not changed much due to port restrictions - it is only 5m longer - it can carry 43 cars - 20 more than Isle of Lewis - and contains 300 lane metres for trucks, compared to Isle of Lewis’ 170 lane metres. The vessel has been designed with an open deck, so it can even carry special cargo like cranes.
The driving factors behind the design of the vessel are reliability and energy efficiency. FSG vice president for sales and marketing Raimon Strunck expanded: “First of all we had to have a reliable service between Ullapool and Stornoway. This service between mainland Scotland and the Isle of Lewis is a lifeline service, so it is extremely important that it is 100 per cent reliable for 364 days a year - 26 December is the only day it is not in service - as otherwise island residents will not receive necessary supplies. They also need a vessel that runs in all weather conditions and is very reliable from the mechanical point of view. We therefore included very high redundancy in the design of the vessel.”
It was for this reason that FSG chose a hybrid propulsion concept - even though CMAL had originally presented a design using a diesel-electric propulsion system. Highlighting the benefits of using hybrid propulsion over a diesel-electric design, Mr Strunck summed them up as offering significantly lower initial costs, better efficiency (with an improvement of up to 7.3 per cent) and a better level of redundancy, as well as allowing four additional cars on the main deck. The design of the pod drive would have reached into the car deck, which is not the case with the FSG concept.
Mr Strunck explained: “A hybrid drive, whereby the diesel mechanical drive goes straight from the main engines to the propeller, is very energy efficient and very reliable. An electric diesel drive, where the main engines work as a generator, generating electricity that is routed through cables to the drive motor, is much less efficient.”
By choosing a hybrid arrangement, the shipyard also added redundancy. It installed two main engines and two auxiliary engines, which are needed for hotel load. These auxiliary engines can also be routed through the main switchboards to the gearbox and so can assist the main engines in propelling the vessel. This means that one main engine can be taken out from the direct line and the shaft line can be run via the auxiliaries. This way service speed can always be maintained, on either one of the engines.
FSG explained that using the auxiliary engines for redundancy instead of investing in an additional main engine saves money as a main engine would be very expensive. It would also take up more space and would lie idle for most of the time. Using the auxiliary engines means that efficiency is improved. These engines have to be installed for hotel loads and so do not lie idle. And they can be used in case redundancy is needed.
Mr Strunck added: “This smart solution means that if you want to take out an engine to be serviced, you can provide normal service by running the diesel-electric propulsion through the auxiliary engines instead.”
Another benefit of Loch Seaforth over Isle of Lewis is that the former runs at less propeller power, at 5,400kW, compared to the latter’s 6,500kw. However Loch Seaforth’s service speed of 19.2 knots is faster than Isle of Lewis’ speed of 18 knots. This is an area in which the hybrid concept gives another advantage: the auxiliary engines can add speed to the main engines, which might be required if the ferry needed to catch up on its schedule after a delay. This booster mode enables the ferry to run at least a knot faster than its service speed; possibly up to two knots faster (the vessel awaits sea trials at time of writing).
Another major innovative feature of Loch Seaforth is its vertical bow design, created by FSG. Mr Strunck said: “The vertical bow design is one of FSG’s strengths. Our expertise is not just in mechanical integration but in developing and optimising the hull design to make it the most efficient.”
Using a vertical bow allows for a longer waterline; using a slanted bow means that the waterline is shorter, given the same overall dimensions. Mr Strunck told Passenger Ship Technology that a longer waterline means that the vessel can be built slimmer with the same displacement. This provides less resistance in the water, which helps in terms of fuel efficiency. Furthermore, the flare above the waterline is less, which improves seakeeping behaviour - there is less slamming and lower acceleration. Mr Strunck added: “Less slamming means that the vessel cuts through the waves. This allows a much higher level of comfort for passengers and cargo, as it does not move up and down so much. Furthermore, cutting through the waves uses less fuel; each time a vessel goes up and down and slams into waves, it stops and the ship has to be accelerated again, which uses more fuel. Cutting through the waves also improves the longevity of the vessel, and reduces maintenance time. Heavy slamming is very stressful on the steel structure and equipment.”
Another benefit of the bow design is that the collision bulkhead moves forward, which benefits the bow door and ramp access. The bow ramp is shorter and the bow door opening is wider and clearer.
Commenting on the innovative propulsion concept and bow design, CalMac’s Mr Dorchester said: “The decision to select this type of propulsion was because of its very high levels of efficiency, as was the vertical bow design. Ferry services are subsidised by the Scottish Government and, as you would expect, it is incumbent upon anyone in receipt of public funding to identify, where possible, solutions which lessen the demand on the public purse.”
The use of FSG’s vertical bow was a change from the initial hullform design originally presented by CMAL. FSG has calculated that the overall hull improvements save 1,400kW compared to the original design. It will also offer fuel and operational savings of over €22 million (US$29 million) over the next 20 years.
In order to achieve this hullform and its associated benefits, FSG uses computational fluid dynamics (CFD) programs and has over 150 in-house engineers working on products and designs of this kind. The concept is unusual. Explaining why it is not in general use, Mr Strunck said: “It is subject to fashion trends. Many owners want a traditional bow line. Also, in order to get a significant benefit out of a design, the designer must have the right computing capabilities. It is only with highly developed CFD tools and experience in calculation that the synchronous interference between the bow wave and the bulb wave, and the resulting flow to the aft end of the vessel, can be achieved. If this synchronisation cannot be reached, the wave pattern worsens and fuel efficiency is reduced. The vessel is, in a manner of speaking, glued to the waves.”
Another innovative feature of
Loch Seaforth is that it uses a Kappel-type propeller, which has tips that
bend upwards at the end of the blade. This increases the efficiency of the propeller and reduces drag, and so has greater efficiency than a normal type of propeller.
Elsewhere on the vessel, an asymmetrical bow ramp has been used because of mooring arrangements in port. Ullapool is a very small port with very small ramps. Having this ramp means that the length and width of the vessel can be accommodated.
FSG also optimised the vessel in terms of its internal design, in order to lower operational costs. Mr Strunck expanded: “The architect considered what the interior would look like. We took the architect’s concept and combined it with the logistical flow within the vessel; for example, from provision stores to galleys to dining areas. We optimised the layout – for example, ensuring that people taking trays of food and those serving do not cross each other, allowing the process of serving to be speeded up. These are small bits and pieces but if you look at the whole concept they add to lower operational costs and higher revenue
for the owner.”
FSG’s engineers and outfitters fitted elements together in the ship to achieve efficiencies by using three dimensional modelling tools. Singling out a benefit of this method, Mr Strunck said: “It shows the layout of pipes and how to do maintenance on the ship. For example, it makes sure there is proper access to the fuel filters when it comes to extracting them. By ensuring this, only one person needs to do the job, which saves time and money. If there is no proper access, another person might be needed to help extract the filters.”
CMAL also had access to the 3D file during the drawing approval process. This meant that it could check to see that the design matched its requirements. “It also meant that there was an active and lively exchange through the drawing approval stage,” said Mr Strunck.
Loch Seaforth can run on both intermediate fuel oil 40 and marine
gas oil. Mr Dorchester commented: “This was to allow choice when selecting fuel grades in service and make the ship as resilient as possible to fuel supply risks.” Asked about the possibility of using liquefied natural gas (LNG) in the future, Mr Dorchester told Passenger Ship Technology: “It is something we are keen to look at as we recognise there are significant benefits to its use. However in the remote and rural areas we serve, significant investment would be required in the shore infrastructure. It is not within our gift to provide this infrastructure but we do believe we potentially have a role as a catalyst to encourage others to do so.”
FSG beat off global competition from other shipyards to win the contract for Loch Seaforth. Mr Strunck said: “We feel we offer not necessarily the lowest price but the best value for money, which is why they went to us. Also, we convinced them about the overall savings our propulsion and hull development offered, which were greater than their initial designs. They could see that they would save a lot of money over the ferry’s lifetime, and have a highly reliable vessel.” PST
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