Concept Ship

January 26th, 2017 by JCB
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Autonomous shipping in our industry is occupying the attentions of designers and engineers in partnership with Flag States and Classification Societies. Over the next few years the proposal of Autonomous Ships is likely to be fiercely debated. Our Association was represented at the Nautical Institute seminar on Autonomous Ships held in September 2015 at Bristol, and our members’ notes from the meeting will be published in the next edition. This article by DNV – GL looks at the feasibility of a small autonomous coastal ship designed to be environmentally friendly whilst delivering cargo packages and is  published with the kind permission of Alexandra Jane Oliver PR Communications Expert, Media and Public Relations, Hamburg  Ed

The Next ReVolt

The EU’s road network suffers from chronic congestion. Yet road usage for cargo transport is steadily increasing, leading to heavier road wear, more accidents and higher emissions. The population growth in urban areas expected over the next decades will without doubt compound the problem, causing the demand for transport to exceed the capacity of today’s roads.

To alleviate these issues, governments all over the EU are trying to move some of the freight volume from the road to waterways and railways. In the short-sea shipping segment, however, profit margins are small due to high energy and operating costs as well as
high taxes.

These circumstances, particularly the Norwegian government’s National Transport plan, prompted DNV GL’s Strategic Research and Innovation department to design a new ship concept specifically for short-sea shipping with the objective of encouraging a modal shift from road to sea. By taking the design and applied technologies to the extreme, the DNV GL engineers want to launch a new discussion within the community while upholding DNV GL’s maxim of a safe and sustainable future for shipping.

The innovative ship concept “ReVolt”, the unmanned, zero-emission, short-sea ship of the future” is the result of a multi-disciplinary, team- based development project at DNV GL based on an assessment of current requirements along European short-sea routes. Nevertheless, the concept could be implemented in other coastal regions around the globe.

Defining the operational profile

ReVolt’s operational profile was established by analysing Automatic Identification System (AIS) data from vessels operating in the Norwegian

Economic Zone (NEZ) in 2012. The relevant routes consist of individual legs of less than 100 nautical miles. The ship type and cargo capacity, which is within the 100-TEU range, were obtained by pairing the AIS data with DNV ship register data. From this information the requirements for the ship concept were derived.

The vessels evaluated in the AIS analysis had an average service speed of 8.7 knots. For ReVolt it was decided to reduce the required speed to 6 knots to allow for more efficient propulsion solutions. As a consequence of this low speed the logistics chain will have to be redesigned entirely to account for longer transit times. However, implementing a “conveyor belt” logistics concept with frequent departures and short, four-hour-average port stays could create the right conditions for transferring appropriate cargo types to this
mode of transport.

Design characteristics

The hull of the vessel was designed to optimise ship efficiency, fulfil all applicable safety and operational requirements and enable operation without ballast water.At the ship’s slow cruising speed the resistance to overcome will consist primarily of hull friction and occasional external forces acting on the vessel. The wave-making resistance will be modest. For this reason a straight vertical bow design was chosen to minimise resistance across the entire operational profile. In addition, a sharp waterline creating a piercing effect is favourable in adverse wave conditions. CFD calculations for the chosen design showed a low calm-water resistance of 50 kilowatts. On the other hand, the added resistance in waves and wind resulting from the low cruising speed was shown to contribute a relatively large portion to the vessel’s overall resistance. Resistance calculations incorporating met-ocean data sets from the intended route revealed an average ship resistance of 120 kilowatts.

An investigation into the possible use of composite materials was also carried out. While the lightweight material would reduce the wetted surface when compared to normal steel, the resulting draught reduction would require a smaller-diameter propeller, thereby compromising the ship’s propulsion efficiency. Therefore a steel hull, which is also less costly, proved to be the best solution.

The propeller design for the ReVolt was largely based on efficiency considerations, since most of the normal design constraints were irrelevant due to the low vessel speed. Since cavitation will be negligible, the number of propeller blades was reduced to only two.
This in turn considerably reduced viscous losses in the propeller. For the final design a propulsion efficiency of 76 per cent was achieved.

ReVolt will operate independent of tugs and needs good manoeuvrability. Because of her hull shape a podded propulsion system was chosen over conventional shafted propulsion; this also reduces the number of rotating parts on the ship. The design calls for two stern pods as main propulsion units plus one retractable bow thruster
for manoeuvring.

A fully battery-powered solution was selected for the ReVolt to maximise efficiency, eliminate emissions and reduce the number of rotating components requiring maintenance. Provided that the batteries can be charged with hydropower, a battery-based propulsion system will be highly efficient and clean. The energy loss from the water reservoir to the propeller is estimated to be as low
as 40%. By contrast, comparable

diesel-powered ships may suffer well-to-propeller losses of up to 85%. Furthermore, using renewable energy to charge the batteries makes ReVolt a zero-emission ship. And finally, batteries represent a low-maintenance solution for an autonomous vessel designed to require as little human interference as possible.

Autonomy through simplicity

Ship maintenance chores are a major portion of a ship crew’s activities. So when a ship operates with a very small crew or entirely without people on board, how can the vessel be maintained? One strategy is to minimise the required maintenance effort, and this is precisely what the designers of ReVolt did. Since the equipment most prone to technical breakdowns is rotating machinery, ReVolt is a ballast-free, fully battery-powered, unmanned vessel with the smallest possible number of rotating components. In fact, the only rotating machinery on board are the components associated with the propulsion pods and bow thruster and are located outside the ship’s hull.

In terms of autonomous navigation, an integrated system comprising ECDIS, GPS, radar, cameras, LIDAR and other sensory equipment has the potential to create complete situational awareness around the vessel. All of the required technology is available off the shelf today.

ReVolt’s autonomy concept takes the applied technologies to the extreme, and DNV GL believes
that many intermediate development steps, such as condition and sensor-based monitoring, enhanced navigational assistance and remote operation, will have to be taken before unmanned ships can become a reality.

Operational and cost efficiency

Since ReVolt sails at relatively slow speed it is essential to avoid wasting time in port. By using state-of-the-art technology in automatic mooring systems, such as grip-arm and vacuum-based mooring, ReVolt will be moored quickly without the need for ropes and winches, which are highly dependent on manual assistance and regular maintenance.

By raising the hull sides and cell guides to full container stack height, cargo handling can be accelerated while eliminating the need for stevedores and manual lashing.

To ensure fast transfer of cargo from the ship to other modes of transportation, the shoreside facilities in ports need to be highly efficient. This can be achieved by building dedicated terminals with easy
access for trucks.

The ReVolt is unique in terms of both safety and environmental performance. However, the question remains whether all this can be achieved at a reasonable cost.

The autonomous capabilities of ReVolt significantly reduce or even eliminate the need for crew facilities, a superstructure and auxiliary machinery, leaving more space for payload. The battery pack on board ReVolt is extremely capital intensive, with an estimated cost of US$1,000 per kWh. And, due to the performance degradation of batteries, the need for a replacement pack means that this cost will be incurred twice over the estimated lifespan of the vessel of 30 years.

As battery technology matures, battery costs are likely to drop significantly. Taking into account local incentive programmes such as the Norwegian NOX-fund, the CAPEX of ReVolt is estimated to be equal to that of a conventional ship with equivalent cargo capacity.

But where ReVolt will truly excel is the cost of operation. Her energy, maintenance and crewing costs will be far below those of a diesel-powered ship; by how much depends on the shoreside infrastructure needed to enable autonomous operation.

As a result, ReVolt will be profitable from day one. Over her lifetime the ship will save about US$34 million in operating costs compared to a conventional vessel. Future governmental emission reduction incentives may further increase the margin. A detailed 1:20 scale model of ReVolt has been built to demonstrate the ship’s autonomous capabilities and test other design features. DNV GL uses this scale model to learn about the challenges and opportunities of autonomous navigation and pave the way to a future where autonomy is part of
the solution for better safety at sea.

 

A vision for the future

ReVolt is a vision for the future and will not be built until several of the technologies involved have matured. However, the vessel could conceivably be built and operated using current technology. ReVolt is intended to serve as an inspiration for

equipment manufacturers, shipyards and shipowners as they endeavour to develop new solutions towards a safer, more sustainable future.

General Particulars

Length overall 60.23m          Beam 14.50m       Draught (full) 5.02m         Draught (ballast) 3.35m

Design speed 6 knots            Capacity 100 TEU/ 1,250mt                             Range 100 nm

Propulsion 2 x Azimuth pods 1 x bowthruster

Questions & Answers on the ReVolt 

Expert: Hans Anton Tvete, Senior Researcher Maritime Transport Performance and Fuels, DNV GL

• Why did you develop the ReVolt concept? The Research and Innovation team at DNV GL was inspired to develop the ReVolt concept by the Norwegian government’s National Transport plan. In this white paper the Norwegian government set the goal of moving more transport from land to sea, facilitating short sea shipping and building maritime infrastructure. These are also high on the priority list for the EU. Therefore, the concept is built around small general cargo vessels in operation in Norwegian coastal waters. But in the future many of the concepts and technologies we use in ReVolt could also be used in other ship routes, for example inland water routes.

• How much would the vessel cost?  We estimate the cost of constructing ReVolt to be approximately US$10 million – the same as a conventional ship of the same size. Over its 30 year life span, due to lower operational expenditure, the ship could save some US$34 million compared to a conventional vessel.

• How does ReVolt enter a harbour? Can the ship identify obstacles such as sandbanks etc. or does it need to be guided into a port? Using technologies such as GPS, ECDIS, radar, LIDAR, AIS and cameras, Revolt can navigate independently because of a multisensory perception field around the vessel. The ReVolt will also utilize port charts so as not to get caught in sandbanks. Each of these technologies is already available. We are also looking into shore side control centres.

• How long does it take to charge the battery? We found the average port stay for the route studied was 4 hours. ReVolt is designed to be fully charged for departure within this time. The battery has a lifespan of approximately 15 years.

• How large is the model that is being tested? ReVolt – original size: length 60, 23 metres; breadth: 14, 5 metresModel (1:20): Length: ca. 3 m Breadth: c.a. 72, 5 cm

• Could ReVolt technology be used on larger ships? Over the medium term we expect many of the technologies used in ReVolt to become more widespread in general shipping. Battery technologies have already been deployed, for example in the vessel Viking Lady – a project in which DNV GL was involved. And as battery prices decrease and they batteries become more efficient, we expect their uptake to increase. Some of the parts of the autonomous systems have potential to help crews operate their vessels more safely, for example an automatic system that would watch for potential hazards, check to ensure the crew takes appropriate action and, as a failsafe, initiates course correction.

• How did you develop the concept?  We used specialized computer software to design the ship and build a 1:20 model. The ship’s parameters were developed using AIS-Data. CFD calculations (Computational Fluid Dynamics) determined the optimal hull form for the route and operational profile suggested by the AIS-Data. We also assessed the hull material, as well as the propeller design,
using CFD.

• If ReVolt travels without captain or crew, how is it quantified legally? Could it be entered by anyone? When we developed ReVolt, we concentrated on the technical feasibility of the project. Before unmanned ships come into use, governments would need to develop a legal framework for them. This does not exist yet. We believe that autonomous vessels first would be introduced in territorial waters, where country-specific rules apply.

• What are the next steps for the project? ReVolt has already been built in the form of a 1:20 scale model. We are currently testing its capabilities in open water in Norway. The next step is to test the autonomous capabilities of the demonstrator.

• Where was ReVolt developed? Were some of the components developed in Hamburg?

ReVolt was developed by the DNV GL Strategic Research & Innovation team in Norway, where it is currently being tested. The technology used in the ship’s design – such as LIDAR, ECDIS and radar – is already commercially available. We combined existing technology to see what is possible and how far we could go with respect to energy efficiency, emissions and safety and still maintain cost effectiveness. We hope that ReVolt can serve as inspiration for ship owners and yards in their efforts to develop new solutions for a safe and sustainable future. DNV GL experts in Germany are also examining concepts and systems for autonomous shipping.

• Has anybody already shown a serious interest in ReVolt?  Companies and governmental bodies have inquired about the autonomous operation of the ReVolt. We see maritime batteries as an emerging technology; several installations are in the pipeline. These installations are mainly focused on short ferry connections and for shipping segments with a varying operational profile, for example the OSV (Offshore
Support Vessel) segment. With ReVolt we introduced this technology to the coastal traffic segment for the first time.

Article: DNV GL ReVolt was published with the kind permission of Alexandra Jane Oliver PR Communications Expert, Media and Public Relations, Hamburg

Images: DNV GL ©Toftenes Multivisjon