Latest experiment in energy-efficient container ship design

We are always interested in latest developments, especially in the transport sector. Andrew McAlpine writes on the container shipping & trade website about Imoto Lines’ latest container ship Natori that is described by the company as ‘an experiment in energy saving’.


The world’s first spherical-bow container ship

The evolution that has been taking place in container ship design over the past few years has been most apparent in larger vessels of the type. It is the increase in ship size, and the quick adoption by most container lines of the ‘twin-island’ superstructure  design for all ultra-large ‘box’ ships that has been the biggest change. And 2017 will see yet another step-up in size with the arrival of the 21,100-container  MOL Triumph.(!!)

As tougher environmental regulations are introduced and the need to reduce operating costs continues to grow, vessel efficiency and environmental impact are increasingly important for all shipping companies, whether they are operating the world’s largest ‘box ships’ or small coastal ‘feeder’ vessels.

One company that is clearly looking at vessel design as a means of improving efficiency is the leading Japanese coastal ‘feeder’ operator Imoto Lines. Headquartered in Kobe, the company has operated domestic shipping services in Japan since it was founded in 1973, when it started a service employing deck barges between Maya-futo in Kobe and Tanoura in Moji. Today it has a fleet of 25 feeder vessels ranging from 190 teu to 540 teu operating on services calling at 56 Japanese ports and providing feeder services under the Japanese flag to international carriers. Many of the company’s vessels have been designed specifically to operate on its niche services that call at a number of small Japanese ports.

In December 2013 the company placed an order with Japanese shipbuilder Kyokuyo Shipyard Corp which has its shipyard in Shimonoseki, the most western city on Japan’s main island, Honshu. The shipbuilder was acclaimed in 2010 when it launched City of St Petersburg, the first of two innovative roro vessels featuring its ‘eco-ship’ design. Both featured its patented SSS-bow, ‘semi-spherical-shaped bow’. Imoto Lines’ new vessel shares this unique bow design.

Launched in December 2015, Natori was, according to Kyokuyo Shipyard, “the result of a reaction between experience and expertise of the two companies.” Its design was the culmination of a project for energy saving using a large coastal container carrier with a next-generation SSS-bow, which received a government subsidy from Japan’s Agency for Natural Resources and Energy –part of a programme to promote energy-saving logistics projects.

Natori has an overall length of 136.2m, a width of 21m and a shallow draught of 9.2m, with a capacity of 7,390 grt. It can accommodate 548 teu which includes 100 reefers. It is currently the largest Japanese coastal container vessel, and has double the capacity of a conventionally designed container ship with a similar hull tonnage.

Its most striking feature is the wind-reducing SSS-bow, which incorporates the navigation bridge and accommodation and is located at the forward part of the vessel. The SSS-bow design was developed by the shipyard to reduce wind resistance and its performance was tested using a wind tunnel. The tests showed a maximum wind resistance reduction of up to 50 per cent compared with a conventional vessel.

Unlike pure car carriers, the wind pressure area varies on a container ship depending upon the load condition, as the height of the container stacks can have an effect. The tests compared Natori’s design with a conventional container ship of the same capacity and with the bridge and accommodation superstructure located aft and in different load conditions. Each time the results showed that Natori achieves greater energy savings, including a 5 per cent reduction in fuel consumption in all load conditions.

The use of the SSS-bow has a number of other advantages when compared to conventional design. With the bridge located forward of all cargo there are no visibility restrictions, which means that increased container capacity can be achieved by loading an extra tier of containers to a maximum of three tiers on deck – as there are no regulations affecting visibility aft of the bridge. The spherical shaped bow also provides extra protection to the containers on deck in heavy seas, as the sea water is naturally deflected away to the sides. The design integrates the bridge and accommodation into the fore part of the vessel, and the spherical bridge is said to improve visibility.

Crew comfort is improved, too, as all accommodation is separated from the engine room, reducing both noise and vibration. Although separated, access to the engine room is vital and is achieved by way of an enclosed passage under the upper deck. The passage is equipped with hydraulic watertight sliding doors and remains unaffected by bad weather or rough seas. An ECDIS system, together with cargo and weather monitoring cameras, is installed and is connected to Natori’s own private network which enables the crew to view both navigation and cargo operations from their own cabins.

A single MAN B&W 7S35MC7 diesel unit with an output of 5,180kW at 173 rpm and built under licence in Japan by Hanshin Diesel Works provides main propulsion. This drives a single 4.1m diameter high-efficiency propeller by Nakashima Propeller Co, giving a maximum service speed of 16 knots.

To help ensure that Natori has excellent manoeuvrability when in port, it is fitted with a single 970kW bow thruster and a ‘mariner’-type Ocean Schilling rudder. This design improves the lift generated by the rudder itself which in turn improves manoeuvrability, especially at low speeds. The rudder can turn to 70 degrees port and starboard.

During cargo operations draught adjustments can be carried out easily thanks to a ballast system supplied by Japan-based Amco Engineering Corp. This system can be controlled over WiFi via a tablet in any part of the accommodation or bridge.

As with most new vessels, a number of eco-friendly features are installed that aim to reduce Natori’s environmental impact. These include an improved underwater hull form, ultra low friction antifouling fuel-saving paint, a fuel oil piping system designed to prevent oil spills during bunkering operations, and IMO PSPC (Performance Standard for Protective Coatings) compliant coatings in the ballast tanks.

Natori has already achieved two awards. The first, awarded at the 17th Logistics Environment Awards organised by the Japan Association for Logistics and Transport, was for the development of technology that reduces the environmental impact of logistics operations. According to the organisers, the award recognised Natori’s innovative energy conserving measures, including the SSS-bow and special propeller by Nakashima Propeller Co,    as well as the ship’s contribution to efforts to achieve a modal shift of freight from road to coastal ships in Japan*.

This was closely followed in July this year by the award for the best small cargo ship at the 2015 Japanese Ship of the Year event hosted by the Japan Society of Naval Architects and Ocean Engineers. Imoto Lines received the same award the year before with its vessel Futaba.

Natori is currently deployed on a service linking the ports of Tokyo, Yokohama, Kobe, Kitakyushu and Hakata.


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