Ropax designers seek efficiencies as capacity ceiling looms




Maximum ropax ferry capacities may have plateaued at 5,600 lane metres, despite strong incentives to meet efficiency improvements via economies of scale, writes Kari Reinikainen. Owners will also have to think of future regulatory considerations with their newbuilding plans.

When Grandi Navi Veloci in Italy introduced its 32,746 gross ton newbuilding Majestic in the western Mediterranean in 1993, the ship was somewhat of a novelty.

It offered good quality passenger accommodation, but its lane metre capacity of 1,725 was much greater than that of Scandinavian cruise ferries of the time, which tended to hover in the region of 1,000 lane metres. By contrast, the ship only carried 1,205 passengers in cabins, which was roughly half of the figure of a similar sized cruise ferry of the time. 

The template was quickly adopted by other operators in the Mediterranean and then elsewhere. The type of vessel quickly became known as a ropax ferry.

Ramping up capacity

By 2010, Stena Line’s 64,000 gross ton sister ships Stena Britannica and Stena Hollandica could offer 5,566 lane metres of vehicle deck capacity, yet they only had accommodation for 1,380 passengers. Pure freight roros of more than 6,000 lane metre capacity have been built since then, but the capacity of ropaxes has not really increased since the days of the Stena Line Hook of Holland-Harwich duo. 

A major reason why capacity growth has halted – at least for now – is that many ports that handle these ships can only receive vessels of up to 230 metres in length, said Anders Orgard, chief commercial officer at OSK Ship Tech in Denmark. 

The port facilities are a crucial consideration not only when it comes to receiving the ships, but also the vehicles that are to be loaded and discharged onboard the ship. The vehicles to be loaded must be accommodated in the port and in case of large vessels, they take up a lot of space.  

“Turn around in ports is another major constraint. Using two tier loading cuts the time needed to load and discharge dramatically compared to the use of just one tier,” he told The Motorship.

Slowly does it

However, the largest pure roro vessels – their lane metre capacity is well over 6,000 – are already struggling to keep schedules due to the use of stern ramps, which pose a bottleneck for these operations. The stern ramps limit the number of tugmasters that move in and out at one time and to tackle that problem, OSK Ship Tech has produced a concept design for a ropax vessel with side doors that will significantly speed up loading and discharging of cargo.  

This again means that the vessel can cruise at a lower speed than a conventional vessel of the same type, which saves fuel and cuts CO2 emissions, Orgard noted. “This design competes with the largest roros, so the range of services and locations where it could be used is limited,” he pointed out.

Another factor that is quite likely to affect the design of roro vessels in the future, ropax ferries included, is what happens in the development of autonomous trucks. “Roros with internal ramps do not go well with autonomous trucks. This can also significantly influence how (roro) cargoes are handled in ports, Orgard said. 

One way of paving the way for the arrival of autonomous trucks would be to arrange the vehicles so that they can be loaded on five tracks across the ship, with one ramp leading to the upper and one to the lower deck, both of which would be connected to a linkspan, he concluded. 

The obvious advantage of roro vessels over e.g. container ships is the fact that roro cargo gets quickly to its destination: containers discharged from a ship are usually stacked in the terminal area or nearby logistics centre to wait for a pick up, while a trailer is quickly connected to a truck and is on its way to the recipient, said Vesa Marttinen, director of cruise, roro and yachts at Wärtsilä, the Finnish technology group.

“However, the capacity of ports and their immediate hinterlands may not have always developed hand in hand with the growth of roro vessels. Once this bottleneck has been removed, we may see larger short sea roro and ropax vessels in the future than what we have today,” he told The Motorship.

Environmental considerations and design

The development of ship designs of the future, of all types of ships, will be heavily influenced by tightening requirements for cutting green house gas emissions. However, these requirements only look at the ship and not the port operations, which may include considerable inefficiencies that affect the overall transport chain. 

A leading theme in the design of ropax vessels is to get the passengers and freight quickly from home to their destination and in these vessels it is the volume that is available onboard that is a crucial bottleneck, not the weight of the cargo like for example in bulkers and tankers.  

Already today it is possible to follow the EU-MRV reporting system that shows transported volumes and the CO2- efficiency of each mode of transport. “This has shown that the most efficient ropax vessels are the ones that can accommodate large numbers of passengers and little cargo, apart from their cars, or the other way around,” Marttinen said.  

“From this it could follow that passengers and their cars may be carried in the future on different vessels than trailers. In this case the number of vessels would grow meaning more material need for the same transportation work. In effect, the tail would wag the dog. Decisions of authorities will be in charge: it is not good if they start to favour one solution. As things stand, optimisation may mean something that the authorities define,” he continued. 

The Energy Efficiency Existing Ship Index (EEXI) that the IMO was due to consider in March is a fairly straightforward question in the case of e.g. bulkers. “However, it is a much more complex question in the case of ropax and cruise tonnage, it may actually influence the designs of the future,” Marttinen continued. He wondered whether unit cargo and passenger transport should be considered to include port operations in the remit of the IMO.

The efficiency – or the lack of it – of port operations plays a significant part an the overall efficiency and carbon footprint in the operations of these ship types. Efforts to optimise only the seagoing part’s performance may result in a sub-optimal outcome when these matters are considered against a broader perspective. 

Lightweight craft code

On a practical note, Marttinen suggests that level playing field thinking between transport modes should gain ground. “Sea lanes do not suffer from wear and tear. Roads do. And to build a railway line, you need space from the carbon capturing nature or from peoples living for the tracks. There has been little discussion about what are the emissions from a ship that is not fully loaded. Passengers want fast connections, but it is the freight that continues to grow in importance,” he added. 

Against this broad spectrum of challenges, Marttinen suggests that the design of future ropaxes on some routes could be based on the international lightweight craft code rather than SOLAS. Their hulls could be built of high tensile steel that is relatively lightweight, while the superstructure could be built of composite materials. (The Motorship considered the issue of composite materials in an article in the April issue.)

On relatively short and sheltered crossings where this kind of design approach might be used, it would be possible to look at the optimisation of various parameters, such as fuel consumption and emissions plus freight and passenger capacity, speed and hence the frequency of service the vessel could deliver, from a new angle. 

Although some investment decisions have slowed during the current coronavirus pandemic, ferry owners in Europe had already launched fleet modernisation programmes and as many companies still have ageing tonnage in their fleets, investment will be needed in the future as well. Finding an optimal design that meets both the commercial and environmental requirements will probably not become easier as times goes by.

Principal Particulars – Early ropax vessels

Vessel name

Year built GT Lane metres

Passenger capacity

Majestic 1993 32,746 1,725 1,205 in cabins, 236 deck

Arethousa

1995 28,417 2,250 500 in cabins, 1,000 deck
Superfast 1 1995 23,663 1,675 626 in cabins, 784 deck

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