Platform for the implementation of a future inland navigation action programme

Options for shallow-water/climate resilient vessels

Juha Schweighofer on climate resilient vessels

Executive summary


According to NAIADES III, the use of the EU’s inland waterway network is currently not optimised due to the lack of coherent infrastructure and fairway quality assurance. Droughts and floods can severely disrupt transport activities by: temporarily blocking waterway sections, imposing restrictions on the amounts of loads transported, and requiring additional vessels to compensate for reduced load factors, or even a shift to other modes of transport. In consequence, under such circumstances, the supply of raw materials and manufactured goods can become insufficient or even interrupted, the transportation costs will increase and the impact on the economy can be dramatic. For example, in the third and fourth quarters of the year 2018, the production losses of the German industry due to persistent low water levels on Rhine river amounted to approximately 4.7 billion EUR. This corresponds to 0.63 % of the entire German industrial production. Several companies had to cope with substantial production losses, like BASF in the order of 250 million EUR and ThyssenKrupp in the order of 100 million EUR.

In general, in the past 200 years, such low water events occurred regularly, although in the last 50 years these events have become less and shorter lasting. However, also in the light of no climate change such events will happen in the coming decades. Accounting for climate change impacts on the hydrology, it is expected that such events will occur more often in the future. For example, in the Rhine area (Lobith) the low water event of 2018 is projected to take place every 10 to 20 years instead of once every 60 years till 2050, according to research findings of Deltares. The impact of the past longer lasting low-water events on inland waterway transport was not that strong as in 2018. The reason is that in those times the vessels were smaller and less vulnerable to water-level changes compared to the much larger new ones which entered operation in the past 20 years. This holds also for a part of the pusher and tug fleet on the Danube which displayed initial design draughts between 1.1 m and 1.5 m in the 1960s and 1970s, while the draughts of most later designed and today’s pushers vary between approximately 1.5 m and 2.2 m, allowing for higher propulsive power, larger convoys and, thereby, for greater energy and cost efficiency of the transport at normal water-level conditions.

Considering these severe impacts on the economy and the inland waterway transport as result of low water, which is being increased by climate change impacts, it is necessary to re-evaluate the logistical concepts in place today, including the size and design of inland vessels. New concepts shall contribute to the reduction of the vulnerability of inland waterway transport to low-water events, and they shall be implemented relatively fast, e.g. within a few years, in dedicated single cases e.g. where severe economic losses due to low water shall be avoided.

However, it is stressed that in order to reduce the vulnerability of the entire EU fleet, comprising more than 12 000 operational vessels (PROMINENT (2015)) of which approximately 40 % are assumed to be vulnerable to low water dedicated infrastructure measures, starting with proper maintenance and management of waterways on short term, have to be considered for improving the climate resilience of inland waterway transport on the long term. The argument is also that such a great number of vessels cannot be replaced within a reasonable time frame, considering the associated costs and available ship-yard capacities. In addition, if infrastructure measures are neglected, the navigation conditions will become worse as a consequence. This would result in newly built shallow-water vessels becoming also vulnerable again to climate change effects, reducing thereby the service quality of inland waterway transport.

Impacts on vessel performance and economy

This report gives a comprehensive overview of the impacts of severe low water on the performance of inland waterway transport and the economy. The impacts can be summarised as described in the following:

  • The cargo carrying capacity will be reduced. The reduction is depending on the ship size: larger vessels are more vulnerable to low water than smaller ones if the load factor is considered.
  • The power demand and fuel consumption increase due to increased resistance and reduced propulsive efficiency and therefore the emissions increase.
  • The vessel speed decreases and the sailing time increases.
  • More vessel movements will be necessary for the transportation of the same amount of cargo.
  • The manoeuvrability becomes worse, which is depending on the ship type. In certain cases, also positive effects can occur.
  • The stopping duration and distance increase due to higher risk of ventilation, reduced thrust and a greater added mass.
  • Starting the movement and operation of a vessel may be prevented by ventilation of the propeller, resulting in a reduction of the thrust.
  • Common pushers with a draught of approximately 1.8 m are more vulnerable to low water than common motor cargo vessels with a minimum draught of approximately 1.3 m as they have to stop operation at around 2.2 m water depth if for squat and safety allowance 0.4 m are assumed.
  • The safety of navigation is reduced due to greater risk of grounding and more vessel movements.
  • The transportation costs per tkm and freight rates increase.
  • The supply of raw materials and transportation of manufactured products can become insufficient or even interrupted.
  • Significant losses in production amounting even to several billion EUR in Western Europe can occur.
  • Finally, goods will be shifted to other modes of transport, which will be difficult to revert, as well as which can cause capacity limitations of climate-mitigation relevant infrastructure like railways. A loss transport demand may therefore also occur as result of relocation of production and distribution facilities.

While several measures for coping with low water are already known from past research, e.g. VBD (2004), this report is focussed on recent findings, being clustered in options for shallow water vessels, most recent developments and dedicated subsidy programmes.

Technical options for shallow-water vessels

Suitable propulsion systems of shallow-water vessels aim at preventing possible propeller ventilation, as well as loss of propulsive efficiency at low water while displaying in the best case no increase in energy demand at normal water conditions compared with similar standard vessels. A very effective measure fulfilling this criterion is the application of a flex tunnel with a ducted propeller, which is a further development of the standard propeller tunnel allowing for optimum performance at normal water conditions without a fixed tunnel, which increases the power demand, e.g. a 10 % reduction of fuel consumption is reported by Damen. At small draught the flex tunnel is activated and prevents ventilation. This product is commercially available from Damen Marine Components. Further measures in addition to propeller tunnel and flex tunnel comprise the application of multiple propellers (e.g. three or four instead of two), reducing the propeller load, however, demanding careful investigations with respect to the proper inflow of the water. In cases with very high propeller loads, the application of ducted propellers is very effective as a part of the thrust demanded will be created by the duct.

A bow thruster improves the manoeuvring behaviour of a vessel, which usually becomes worse with decreasing water depth. The stopping distance and time, increasing with decreasing water depths, will be reduced due to the additional thrust of the bow thruster acting in opposite direction of the movement of the vessel and braking it. It supports also the vessel movement from standstill as it provides additional thrust reducing thereby the high load of the main propulsion device and the risk of cavitation and ventilation.

The draught of a vessel can be reduced by several solutions for weight reduction comprising the application of high tensile steel, other material than steel like aluminium alloys, composites and even wood in combination with steel, Sandwich Panel Systems, adhesive bonding, optimised framing, and weight optimisation by direct strength calculations. The impact of light weight solutions on the draught of a cargo vessel is very limited. According to the ECCONET project, for larger vessels, a draught compensation of around 10 cm was obtained (ECCONET (2012)). However, lightweight solutions can be combined with other measures, e.g. the increase of the width (beam) of the vessel, for minimisation of the draught. Lightweight solutions are expected to increase the construction costs, and one has to make a case-by-case decision is the minor reduction of draught worth this cost increase.

Shallow-water hulls and concepts for new buildings to be operated on the Danube have been developed in the recent years:

A pusher with superior shallow-water performance compared with common standard pushers with a draught of approximately 1.8 m was developed featuring the following characteristics: LOA = 30 m, BOA = 11.00 m, H = 2.5 m, T = 1.4 m, three diesel powered drive trains with 700 kW each, three ducted propellers in tunnels, bow thruster 250 up to 300 kW. Taking into account the benefits of the application of the latest technological achievements increasing efficiency, safety, environmental performance and comfort, a new pusher design will be most probably superior to a conventional elder design created according to the standards 30 or more years ago. This report contains a set of guidelines for the design of a Danube shallow water pusher taken from Radojčić et al. (2021).

Starting with the Innovative Danube Vessel project (IDV (2014)), several developments with respect to shallow-water motor cargo vessels were carried out, finally resulting in a wide-body self-propelled X-type vessel for the Danube, displaying a design draught of 2.3 m and a respectable deadweight of 2248 t. The low draught was achieved by increasing the width and reducing the height of the vessel, combined with direct strength calculations and goal-based design of its structure resulting in a light weight not exceeding the one of a standard design, although partially strengthening of the structure had to be foreseen. The propulsion system is diesel powered with twin ducted propellers (propeller diameter = 1.55 m).

In the Horizon 2020 EU project NOVIMAR, two shallow draught versions of the NOVIMAR Class Va container roro vessel have been designed with the purpose to enable navigation in shallow waters such as parts of the river Danube and the Rhine: one “stern access version” concept and one “double end access version” concept. The shallow draught design comes unavoidably with a number of draw-backs. With no cargo below the main deck, the space utilisation and cargo space capacity are reduced as well as the stability due to a higher centre of gravity. However, the concepts have the potential to provide attractive waterborne services, where available water depth is a significant limitation. The maim dimensions are: LOA = 104 m, BOA = 11.45 m, H = 3.0 m, T = 2.0 m, TEU = 104 (a’ 11.3 t, deadweight = 1317 t, first version) and 100 (a’ 11.8 t, deadweight = 1298 t, second version), up to three tiers of containers are possible, PB =2 x 550 kW (2 x 750 hp). 

Also for operation in the Rhine area, several tanker concepts have been developed which are already now in operation or which will enter operation in 2022 and in the coming years, see below: “most recent vessels concepts under construction and in operation”.

The creation of additional buoyancy was initially investigated in the FP7 EU project ECCONET. The basic idea is based on devices creating additional buoyancy when needed for coping with low water. Under favourable conditions, close to those for which the ship is actually optimised, the devices would be put away and the ship would continue the service with optimal performance. Based on the first results, further development is being carried out in the Horizon 2020 project NOVIMOVE, including more detailed performance calculations and comprehensive design activities. Solutions for the creation of additional buoyancy are moveable side blisters made of steel of different shapes or inflatable devices like membrane air pads. Further solutions comprise foldable buoyancy elements integrated into the ship’s body which can be laterally extracted. At present, practical experiences of side blisters in use, be it cylindrical or laterally foldable solutions are not known yet. Finally, the usage of a dock ship taking a vessel onboard at a reduced final draught of the transportation system has been considered in NOVIMOVE. The conceptual design of a dock ship is oriented towards a selected bottleneck, e.g. a distinct shallow water area. To pass short sections of the fairway with insufficient water depth, two different attempts are conceivable to help loaded vessels; on the one hand a powered dock ship and on the other hand a similar module without own propulsion system.

Stakeholder interviews

A comprehensive set of stakeholder interviews is available in Scholten and Rothstein (2012). 417 persons representing shipowners were asked for an interview, 55 complete questionnaires were returned.  According to the shipowners interviewed the following adaptation measures relating to ship technology can be thought of as feasible: modified aft-ship form, additional usage of (smaller) vessels, construction and provision of smaller vessels, 24-hours operation of vessels, usage of light-weight materials, better adaptation of the amount of cargo to be loaded to available fairway depths, as well as improved manoeuvrability. Arguments against the measures listed are mainly the associated costs and minimum draught of vessels being not reduced, as well as shortage of staff if vessels are to be operated 24 hours per day. Here some potential for improvement was observed: only about one third of vessels involved in the interviews were operated 24 hours a day, although 75 % of the vessels had two or more persons with a boat-master certificate on board, allowing for 24-hours operation. Finally, the importance of financing smaller vessels by banks was highlighted.

Most recent research

FlaBi: The overall objective of the joint project “FlaBi” is to increase the resilience of inland vessels during pronounced periods of drought by extending their operational limits. To achieve this goal, innovative ship designs with suitable propulsion systems in combination with lightweight structures are developed for the requirements of the Rhine and Elbe river at extreme low water levels. In addition, a retrofit concept for propulsion and steering devices are developed for the existing fleet, which will improve suitability for extreme low-water conditions. In the sub-project “FlaBiTec”, DST is investigating three different propulsion concepts, a 2nd generation blade-chain drive, a modified paddle wheel drive and the conventional ducted propeller with regard to their operational limits. The appropriate integration of the propulsors into the ship’s hull represents a major challenge. In addition to different propulsors, design measures to reduce the lightweight are also being investigated. The technical developments will be suitably combined in dedicated ship designs. Subsequent model tests serve to identify the operational limits of the designed ships and enable a comparison with existing ships.

Duration: December 2020 – November 2023.

DüPro, based on the outcomes of the project “Determination of the effective propeller inflow for inland navigation” of DST focussed on systematic investigations of the complex interactions between ship, propulsor and waterway. For this purpose, numerous propulsion and open water tests with different arrangements were carried out. Building upon the results of the propeller inflow project, two of the hull forms tested there were built on a larger scale, so that additional information on scale effects could be obtained. In addition, one aft ship each with rudder propellers and the modern flex-tunnel concept was designed, built on a model scale and tested. The investigations were supplemented by CFD simulations and PIV measurements.

Duration: November 2018 – May 2022

NOVIMOVENovel inland waterway transport concepts for moving freight effectively is a Horizon 2020 EU project which focusses amongst others on smart river navigation by merging satellite (Galileo) and real time river water depths data; smooth passage through bridges/locks by a dynamic scheduling system for better corridor management along the TEN-T Rhine-Alpine (RALP) route; and concepts for innovative vessels that can adapt to low water condition while maintaining a full payload. Some of the measures mentioned above with respect to additional buoyancy were already preliminarily considered in previous projects like the FP7-ECCONET (steel side blisters, inflatable blisters and foldable buoyancy elements as theoretical concepts). Building upon the preliminary results, in NOVIMOVE further developments are carried out aiming at raising the Technology Readiness Level (TRL) of these concepts. The corresponding work includes iterative detailing of hydrodynamic characteristics, regulatory and operational aspects, determination of related investment costs (CAPEX) and operating cost (OPEX) as well as structural design. For the latest developments, the reader is advised to visit the website below.

Duration: June 2020 – May 2024

Practical implementations: most recent vessels concepts under construction and in operation

The BASF shallow-water tanker is a highly innovative vessel currently under construction to enter operation end of 2022. Following the experience with the low water levels of the Rhine in 2018 when a suitable ship and sufficient alternative transport capacity was not available, BASF decided to acquire a dedicated tanker in order to secure its production at Ludwigshafen. The vessel features the following characteristics improving its performance at low and normal water conditions: increased main dimensions: L = 135 m, B = 17.5 m instead of L = 110 m, B = 11.4 m; improved cargo carrying capacity at low water: 650 t at T = 1.2 m, and 2500 t at T = 2.05 m; diesel-electric propulsion system with stage V engines for very low emissions; three electric drivetrains with three propellers optimised for shallow water operation and normal water conditions; the outer propellers have a smaller diameter than the centre propeller which ensures additional thrust at normal water conditions; three rudder blades behind the outer propellers for sufficient rudder force, one rudder blade at the centre propeller; one integrated Van der Velden® FLEX Tunnel left and right of the outer drive trains; hydrodynamic optimisation using model tests; lightweight construction ensuring high structural stability by transferring methods from seagoing shipbuilding to inland waterway vessels.

The HGK gas tanker “Gas 94” entered operation in September 2021 as answer to the low-water event of 2018. A contract for the construction of second tanker to be delivered in 2023 has been signed in 2022, and five additional vessels are to follow in the coming years. The improved shallow-water performance has been achieved by proper design and engineering and not by usage of alternative materials. The vessel displays the following features: L = 110 m, B = 12.5 m (slightly increased breadth instead of 11.45 m) , depth = 5.6 m; voluminous foreship; diffusor-like aft ship preventing ventilation at low water depths; small propeller diameters; reduced draught by 30 to 40 cm; Power Management System and diesel-electric propulsion: three ducted rudder propellers, each driven by a 405 kWe electric motor: 30 % less CO2 emissions; optimisation of design of cargo tanks for weight reduction; higher construction costs in comparison with standard vessels.

Dedicated subsidy programmes

In Germany the importance of coping with climate change impacts on inland waterway transport has been acknowledged in the national funding programme for the sustainable modernisation of inland vessels (Richtlinie zur Förderung der nachhaltigen Modernisierung von Binnenschiffen vom 24. Juni 2021). It supports amongst others dedicated measures for optimisation of cargo vessels for improved operation at low water. This can comprise for example: exchange of the aft ship by another one; optimisation of the aft ship by different constructive implementations, optimisation of the foreship by constructive modifications for reduction of resistance; installation of assistance solutions for improved manoeuvring, e.g. bow thrusters.

Following the same reasoning, In Austria, a subsidy programme containing similar items as the one of Germany has been initiated by the Federal Ministry for Climate Action, being currently under evaluation.

Needs for further development

In general, it is necessary to re-evaluate the logistical concepts in place today, including the size and design of vessels. According to the CCNR, the consideration of smaller vessels being able to be operated together with a lighter will gain more significance. In addition, research and development activities targeting existing vessels, as well as new buildings will be required. Such new concepts will contribute to the reduction of the vulnerability of inland waterway transport to low-water events, but they will not solve the problem what for additional measures with respect to climate resilient infrastructure, provision of reliable information with respect to navigation conditions, as well as logistics and vessel operation are required. While measures for adaptation of existing vessels are relatively limited (exchange of the aft ship could be viable solution), aiming largely at increasing the cargo capacity at low water, new buildings show a greater potential for implementation of a number of measures, e.g. lightweight solutions, multiple propulsion devices, hull-form optimisation, variation of main parameters, etc., resulting in improved shallow-water performance and competitive performance at normal water levels.

More research is needed with respect to the provision of reliable data on and forecasting of environmental framework conditions as a precondition for the proper retrofitting and design of inland waterway vessels. The adaptation measures shall not negatively affect the operation of vessels at normal navigation conditions, e.g. increasing the energy demand.

Better understanding of the real sailing profiles allows the vessels to be designed more in line with the real conditions, which is also required for the energy transition. The ship design has to be optimised for the real operating conditions, taking into account rising OPEX with sustainable energy carriers, new ship main dimensions, structures, drivetrains, hull forms and the associated hydrodynamics. Showing still a lot of room for improvement, manoeuvring models for automatic navigation shall be developed, leading possibly to a business case for smaller units, e.g. due to lower personnel costs as a part of the ship operation may be carried out automatically with less personnel. In general, measures relating to the improvement of the competitiveness of smaller, less vulnerable vessels in comparison to bigger ones shall be elaborated, including the creation of regulations for proper implementation. Investigations of extreme shallow water conditions request further research with respect to interaction with river beds and squat effects in combination with small under-keel clearance.

Reliable and efficient prediction of ship operation with ventilating propellers is to be further investigated. In general, model tests and numerical methods can be used for this purpose. Challenges of model tests relate to the assessment of scaling effects, correct propeller loading and application of proper friction deduction force. Numerical simulations are associated with high computational costs for large-Reynolds-number simulations and propeller modelling. Further challenges relate to turbulence modelling and free-surface capturing. The objectives to be achieved are save accelerations, save stopping and save manoeuvres.

Finally, the impact of the introduction of new low-emission or zero-emission solutions for coping with the climate objectives of the EU, increasing eventually the weight and size of vessels, e.g., by full-electric sailing or usage of hydrogen and fuel cells, has to be considered with respect to proper operation during low-water events.

With respect to the adaptation of the fleet, a dialogue between industry, logistics, politics, and environmental organisations, as well as regulations and funding for modernisation on European level will be necessary. Proper cooperation between the different stakeholders and an integrated approach for coping with climate change is necessary, what for also the European institutions are needed.

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