Designing the First UK LNG Ferry

In 2012 Caledonian MacBrayne Assests Ltd (CMAL) began the process of  defining the parameters and arrangement for the ferry that would become the First UK LNG Ferry. It was required to operate in  the majority of the Scottish Highland and Island ports serviced by operator Caledonian MacBrayne Ltd. (CalMac).  From the very first discussions with potential suppliers, the vessel was to be an LNG fuelled vessel.  CMAL and CalMac had already shown their clean energy  credentials in the building of two 43m Ro-Ro hybrid vessels but,at the time, there were few conventional LNG Fuelled Ro-Ro Ferries. Restricted water double ended ferries were the common LNG ferry application.

Initial design development was further progressed in 2014 to allow CMAL to enter into an EU tendering prequalification process.  Ferguson Marine Engineering Limited (FMEL) successfully prequalified and, in 2015, participated in the resulting full tendering process. Houlder was engaged with FMEL to support them with development the tendering design and technical documentation during this phase.

This proved successful and a contract as signed to build two vessels – hull no. 801 and 802 – was signed in late 2015, with delivery of both vessels in 2018.  The principal particulars of the LNG ferry are as below.

Length Overall 102.40m
Length Between Perpendiculars 97.80m
Breadth Moulded 17.0m
Depth to Main Deck 5.95m
Depth to Passenger Deck 12.20m
Normal Operational Draught 3.40m
Design Draught 3.60m
Scantling Draught 3.70m
Deadweight @ 3.40m (approx.) 900 tonnes
Deadweight @ 3.60m (approx.) 1180 tonnes

With dual fuel direct drive main propulsion engines, with power take off (PTO).  The ships main generators are also to be dual fuel each with approx. 900 kw capacity.

The vessels are to be British Flag and classed with Lloyds Register with the following notation: –

100 A1, Roll On-Roll Off Cargo and Passenger Ship, LMC, PCAC2, UMS, IFP, IWS, SCM, NAV1, ECO, LI, IHM, EU (B) GF, Green Passport

On contact award, Houlder was appointed by FMEL as naval architects for the basic design and that work, and further scopes involving more detailed design, continues as the build of the vessel progresses.

Working on the first UK LNG ferry means that Houlder has had to draw on our extensive experience of LNG from other sectors and our 30+ years of ferry design experience. Even with this experience there were some new lessons we had to learn and challenges to overcome.

One example was that the vessel had some fixed size parameters. The beam of the vessel was set at 17m (Moulded) and the depth was constrained to 5.95m due to the various ports and existing linkspans it would service. In addition to this, deck loading from the carriage of wheeled vehicles on the main deck defines the size of deck traverse. In addition to this, it was also calculated the vessel’s required range meant needed a 149 m3  fuel tank.

The UK LNG ferry fuel tank had fixed size parameters of its own. It fitted into the available space however without the required clearance for ventilation and inspection

The solution was to design curved deck transverse beams that allowed space the necessary clearance without compromising the strength of the deck or adjusting any of the loading deck heights.  A typical composite cross section of the vessel shows the seat and the curved deck beams is shown below.

Designing the first UK LNG ferry has required innovative solutions to maintain the vessel’s preferred size requirements. These lessons will continue to drive Houlder’s knowledge and design practice.

For enquiries regarding LNG fuelled vessels, please contact enquiries@houlderltd.com or call the Marine Design Consultancy team on + 44 (0)23 92875277.

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Rupert Hare, Chief Executive Officer

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