Safe and swift performance, a conceptual assessment of a new river sea pusher system

Safe and swift performance, a conceptual assessment of a new River Sea Pusher System

M.B. Duinkerken (Delft University of Technology, the Netherlands)

Abstract

The River Sea Pusher System is a new logistic concept for transferring cargo between ports in the European hinterland and overseas destinations. The concept comprises of push barges, covering the trip from origin to destination, switching pusher tugs with either a river or a sea going capability at a near coast base. Barges and pushers are linked through the ‘Articouple’ system. The system provides an alternative for short sea shipping and truck-ferry transport. Based on previous work, a combined study into the risk assessment and logistic simulation revealed the potential of this innovative system. The logistic performance of a ‘minimal’ implementation was simulated, dealing with vessel performance, infrastructure restrictions, traffic environment and safety critical phases of the journey. Accidents and incidents prove to not only inflict damage to the vessels or jeopardize the societal acceptance of a new system, but also may cause delays in operational practice, reducing the performance of the system. The simulation proves that it is profitable to create synergy by acting upon minor delays and to ensure safety in order to enable swift and smooth operations of the River Sea Pusher System and consequently, to guarantee the availability of the system.

1. INTRODUCTION

Applying a River Sea Pusher System is submitted to national and international maritime regulations in inland shipping as well as maritime shipping. The North Sea is one of the busiest sailing areas, while the Rhine River is an artery of European inland shipping. Both areas are submitted to a wide variety of sailing and weather conditions.

Inland shipping is undergoing a series of major changes, triggered by changes in inland shipping itself as well as by its societal context. Several institutions and organisations play a dominant role, while an increasing number of constraints and restrictions are to be taken into account of both a technical, economical, environmental and societal nature.

A variety of internal factors play a role in assessing the performance of inland shipping with respect to economy, safety and environment. The increase in scale of vessels is economically challenging, but restricted by fairway dimensions and critical size of infrastructure components such as bridges and locks. The natural fluctuation of water heights and local shallowness of the rivers restrict the length of vessels to 135m and 4.50m draught. During extreme low water heights, additional restrictions are taken into account in order to prevent blockage of the fairway or damage to the vessels, infrastructure and environment.

In addition, traffic density and composition of the fleet has its influences on shipping safety. Due to congestion and fairway limitations, bottlenecks may occur at sharp bends in the river, strong currents, junctions of fairways and manoeuvring in the vicinity of bridges and locks.

Inland shipping may be characterized by a continuous, evolutionary technological change. Based on new technology and introduction of new demands, a permanent adaptation of safety rules and regulations occurs, such as the introduction of poor visibility radar support, improving of vision lines and retractable wheelhouses. It is the policy of the CCR (Central Commission for Navigation on the Rhine) to limit the number of long-lasting exception rules and to move forward to certification based on equivalence. This implies that by ranking vessels and equipment into modules for innovation, modification and repair, each new module would be submitted integrally to the regulations in force.

In addition to these internal factors, a number of external factors have had their influence on the safety of inland shipping. The increasing growth of cargo transport has had its pressure on the road network, causing hindrance to the civilian population and surrounding land use and causes concern with respect to the environment. These concerns have lead to a shift in transport policy making objectives, aiming at a modal split and modal shift to railways and inland waterways, optimization within each modality and incorporation of so far external factors in transport policy making issues. In her plan for Vessels for the Future, the CCR identifies the reinforcement of safety and environmental aspects as a spearhead for increasing the competitive capability of inland shipping [1]. To this purpose:

- the risks of waterway transport should be known beforehand based on risk analysis

- an increased responsibility may be demanded in maintaining the achieved safety level accompanied by an increased accountability in case of accidents

- inland shipping may reckon on a reduced financial burden in charging external costs to the sector compared to its competitors in road and rail.

In developing a favourable political climate and societal profile, safety and environment are decisive criteria for modelling inland shipping of the future.

To this purpose, three areas for a further development have been identified as critical:

- the assessment of innovation in inland shipping will be dependent on an effective shift from roads to shipping and development of new market segments. Sustainability criteria will deal with zero emissions into the environment. High demands will be put on protection of the cargo, in particular regarding the transport of hazardous materials.

- the man-machine relation in inland shipping has reached it third generation. Advantages are in an improved predictability and reliability of the trips and improved safety. This third phase deals with improvement of vision lines, on-board digital description and virtual representation of the navigation and nautical communication tasks as well as shore based support. The role of the skipper and his mental load may however change to such an extend, that he may loose oversight and situation awareness. His ability to manage critical and emergency situations and interactions with other traffic participants should not deteriorate.

- in order to facilitate the transport of hazardous materials in the Netherlands by inland shipping, a formal quantitative risk analysis is required. After the firework explosion in Enschede, also for inland shipping, external risk has added a new dimension to safety. In the Netherlands, a Risk Contour Map has been established for specific situations with respect to spatial planning and land use issues around the main waterway network, sites with structurally high density activities and reduced self-relianceness in emergency and disaster management. This put restrictions on the availability of the waterway network [2, 3].

Finally, after the World Trade Centre attacks, major changes have occurred in international shipping. The IMO has drafted a Code on International Ship and Port facility Security. All 134 terminals of the Port of Rotterdam comply with this Code, covering sea going transport. For inland shipping, this security code covers vessels over 500 BRT. For pusher barges however, a grey area exists to which extend the barges, pushers or tugs have to comply with this regime. The use of push barges in the RSPS system raises the question whether or not this system has to comply with the ISPS Code. The security issue however, is not covered in the present research [4].

In combination, these internal and external factors have set the framework for a further assessment of the feasibility of the River Sea Pusher System. Based on the results of earlier work on the technical and nautical feasibility of the vessel as a concept, an analysis on the logistic and safety performance was conducted by the TRAIL Research School of Delft University of Technology [5, 6, 7, 8]. This research aimed at establishing the conditions for a ‘minimal’ implementation of the concept on connecting the Ruhr area (Germany) with the Humber area (UK) under conditions of a ‘societal acceptable’ safety performance. To this purpose the notion of ‘integral safety’ is applied, covering safety aspect of a varying nature such as technical, nautical and maritime safety, working conditions on board, external safety and rescue and emergency services in case of disasters.

2. THE RIVER SEA PUSHER SYSTEM CONCEPT 2.1 performance assessment

The River Sea Pusher System (RSPS) is a new logistic concept to transport cargo between European hinterland ports and over sea destinations. The concept applies barges, which travel the trip from origin to destination. At sea the barges are pushed by a pusher tug, on the river they are pushed by a river pusher. The cargo remains in the hold of the barge, without transhipment in a sea port. The barges switch pusher tugs, enabling a further integration of sea and river transport. The system provides an alternative for short sea-shipping and truck-ferry transport [9, 10, 11].

The minimal implementation consists of two barges, one river pusher and one sea pusher. The river combination sails from Duisburg across the Rhine via Waal and Merwede towards Rotterdam. The sea combination sails from Hull across the North Sea to Rotterdam. In the Rotterdam area the pusher tugs are switched, after which the combination sails along to their destinations.

The anticipated speed at sea is about 12.5 knots (23 km/hour), while the upstream speed on the river is about 11 km/hour and downstream speed is about 19 km/hour. Taking into account these speeds and estimated time for loading, unloading and switching of the tugs approximately three trips per week are foreseen in both directions.

To a high extend the weather conditions at the North Sea and the water heights on the river will determine the logistical performance of the system. The weather on the North Sea will determine the maximum travelling speed, while the water heights on the river will determine the maximum loading capacity of the system. A crucial aspect in the logistic concept is the timing and the location of the switch of the pusher tugs in the Rotterdam area. This new concept may be sensitive to disruptions and delays which are not known with other existing cargo transport concepts. To this purpose a logistic simulation model is designed and tested. Based on a reference scenario, several operational conditions are investigated and the sensitivity of the system is determined for a series of parameters which may cause delays and cancellations.

In addition, by applying an ‘integral safety’ concept, the use of a conventional certification process for assessing the maritime and nautical safety at a systems components level and the use of a quantitative risk assessment for establishing acceptable performance with respect to external safety runs short in assessing the overall performance at a systems level.

To assess the integral safety at the RSPS systems level, two additional safety assessment strategies were applied to establish critical classes of events with different order of magnitude and consequences [12]: - accident and incident analysis prediction of the system, based on analogies with parent vessels and

shipping activities, fairway and safety perceptions by the lay public and press

- an overall system decomposition in order to identify and analyze potential hazards and failure modes, based on the primary working processes of the RSPS concept.

The parameters and assumptions for the simulation and the safety assessment are based on previous results of the RSPS conceptual design assessment [13]. The characteristics of the barges, pushers and coupling devices are derived from research results from the Maritime Research Institute and the engineering project by Damen Shipyards in the Netherlands [14, 15].

An artist impression provides a picture of the RSPS concept as follows. Fig 1: Artist impression RSPS

2.2 Basic parameters and assumptions

regular vessels. Spills of hazardous cargo will be contained within the vessel itself by sump tanks,

complying with Marpol regulations. The wheelhouse is located at the bow, can be elevated 5m to keep free from green water and provides redundancy in navigation and control functions. In addition, this position at the bow reduces the exposure to high acceleration and noise levels for the crew compared to a position at the aft of the barge, which otherwise may exceed crew comfort levels. This position also eliminates the

hindrance of vision lines from high cargo stacks of containers [16, 17]. Applying barges and pushers as two self-supporting units provides additional redundancy in accommodation and during eventful situations at sea.

The barges are equipped with two thrusters fore and aft, 400kW each. These thrusters are remote operated from the wheelhouse. All fire fighting, self-relianceness and emergency assets comply with SOLAS regulations. Since the barges do not exceed the length, width and draught limitations for 4 barge pusher combinations, short sea coasters and vessels with retractable wheelhouses, it is not expected that sailing the RSPS concept will cause more difficulties than other categories of vessels with critical sailing dimensions. Since the barges are built for sea going conditions, they have a redundant robustness compared to inland shipping barges and vessels.

The pushers discriminate between river pushers and sea pushers in their operational practices. In order to apply the barge on the river an additional pontoon is required to fit in between the barge and the pusher. The vessels are connected by steel wires and winches. The pusher brings the barge to the quay and separates from the barge, after which the barge is brought to the jetty and is loaded or unloaded.

Fig 2: river pusher

For the pushing function at sea the ‘Articouple’ systems is applied. This coupling device consists of a two-point connection, enabling a hinging movement between barge and pusher. The construction proves to be reliable as demonstrated by towing tank tests performed by Marin. These hinging movements may reach critical values at sea due to heavy waves. Existing sea going pusher tugs may be retrofitted with the ‘Articouple’ system. The ‘Articouple’ has proven its reliability during various sea going applications across the world, in particular in the Botnic Sea area.

Essentially, the ‘Articouple’ is a hydraulic operated jack-screw which can be locked on into the barge stern at various levels, depending on the draught of the barge. The rotating capability of the hinge allows the barge and pusher tug to compensate for the wave induced pitch of the vessels.

Fig 4: Articouple system

The main advantage of the RSPS concept is that regular sea pushers and river pushers can be hired and retrofitted with the ‘Articouple’ system without the cost for specifically designed new build vessels. In case of cancellation of a vessel, a replacement vessel can be available on a relative short notice.

3. LOGISTIC SIMULATION

The sea reach is calculated along a geodetic line, being the shortest distance between two points on the globe [18]. This creates a route length from Hull to the Maasvlakte of about190 Nautical miles (352 km). The inland shipping route length from Duisburg to the Maasvlakte of 245 km. The transhipment system has an estimated capacity of 30 moves/hour for containers and 20 moves/hour for trailers. The required time for switching from sea to river pusher is estimated at 2 hours, irrespective of crew change, fuelling etcetera. For sea travel, the speed is a function of climatic conditions, in particular wave heights and direction, distinguishing 5 categories: head seas, bow-quartering seas, beam seas, stern-quartering seas and following seas. Sea travel is cancelled with a wave height beyond 6 m, taking into account the risk of green water.

table 1: Speed as percentage of maximum speed Speed in %

Wave height Head BowQ Beam SternQ Follow

> 6.0 m 0 0 0 0 0 For river travel, the keel clearance between the bottom of the vessel and the river bed is decisive, determined by draught and water heights. In order to provide a maximum loading capacity, a minimal keel clearance should be guaranteed.

In addition to the minimal keel clearance, a maximum height of the barge is important to keep free from road bridges across the river. With three layers of containers, the height of the barge is about 12 meters, which is not sufficient for a guaranteed height of 9.10 meters for road bridge clearance. Occasionally, the barge cannot be loaded to its maximum capacity or can be compensated by taking in ballast water in its slump tanks.

In order to maintain maximum flexibility, the switching point for changing pusher tugs has been kept adaptive in a range between the inland city of Dordrecht and a point close to the North Sea, covering about a 50 km distance. In case a delay exceeds 24 hours, a rule of exception is used, simultaneously cancelling the departure in Hull and Duisburg. In case of an early arrival, the time gained is used to compensate for delays encountered earlier during the trip.

For the test run of the reference situation, actual weather and wave condition data over the period 1980 to 2000 are applied. The results of the scenario test run indicate that late arrivals in Hull are higher than in Duisburg. This is caused by the variance of the trip time which is most influenced by the wave conditions on the North Sea, which in turn are dependent on the yearly fluctuations in weather.

The reference test was conducted with a maximum sea travel speed of 12.5 knots and a river speed of 8.1 knots. A sensitivity analysis of a varying speed in practice between 10 -12.5 knots at sea and 7.2-8.1 knots at the river indicated that the number of delays increased considerably with reduction of actual travel speed, while the number of cancellations also increased. Also the wharf carne capacity became critical with increase in travel time delays, since the effects of travel time and transhipment time are cumulative.

The location of the switching point proved to be sensitive to travel speed and delays. In the reference scenario switching at the Maasvlakte proved to be more profitable than switching at Dordrecht, although a rescheduling of the planning could have a beneficial influence on the actual switching location selection..

In the reference scenario the keel clearance is set at 30 cm. The influence of the water heights on loading capacity proved to be significant. Increasing the keel clearance has a distinct influence on the number of cancelled departures.

In the simulation, the recovery time of the system is defined as the time required to reduce the delays after disruption to zero. The recovery time is expressed by the number of cycles. With three departures per week, one cycle time requires 56 hours. From the simulation results, it is demonstrated that delays shorter than 8hours can be compensated within one cycle. Delays up to 16 hours are compensated within an average of 2 cycles, while a 24 delay requires an average recovery time of 3.25 cycles, slightly more than one week. Since the recovery time is measured at the switching point, even a small disruption of one hour requires at least a recovery time of one cycle.

In conclusion, the logistic simulation demonstrates that the reliability performance of the RSPS concept is excellent. A timely departure of 99.6% of the trips is achieved. The arrivals score 96.0% on time. Neither departures in sailing down the river are cancelled due to low water heights, nor to storm at the North Sea. Delays, encountered by storms are compensated during the following trips.

The performance is highly dependent on the travel speeds which can be achieved. The sea speed should be at least 11.5 knots while the river speed should be at least 7.7 knots in order to achieve three cycles per week with a certainty bandwidth of 99%. Only two cycles should be cancelled.

The loading capacity over a 20 year simulation period is 91.6%. Only low water levels have influenced this performance, while the influence of high water levels on the loading capacity in the future is not to be excluded. The assumptions for keel clearance however have a significant influence on the loading capacity during low water levels.

Wharf crane capacity has a major influence because long transhipment times reduce the capacity to compensate for delays. The assumed 30 moves per hour are a prerequisite for a proper performance of the system. The switching point should be selected close to the seaside, but the variance in travel times may be considerable. Any simulation model is a reduction of reality. In the simulation scenarios, the river speed is assumed to be constant in contrast with the speed on the North Sea. A lower river speed may render it impossible to maintain the time tables. In practice the river speed may be influenced by several variables:

- congestion at bottlenecks

- service schedules of bridges and locks

- variance in water heights and bends in the river - variance in current strengths of the river.

In addition, small disturbances in the primary processes may have a significant influence on delays and may even render the system inoperable due to cancellations and barge or pusher tug breakdown.

4. SAFETY ANALYSIS 4.1 Accident data analysis

Based on the accident data over the years 1996-2002 with push barges as the most equivalent type of shipping, an analysis was performed on the probability of accidents with the RSPS concept. No information was available from foreign accident data bases [19]. Push barge accidents most frequently occur in the higher upstream parts of the fairway in the Nijmegen and Tiel region. It can only be concluded that similar accidents may occur with RSPS on these existing black spots in the Dutch part of the fairway.

Based on a categorization of accidents in various types it can be concluded that: - almost any accident (250 out of 280) occurs with sailing over moored vessels

- there is an overall decreasing trend in accident frequency over the years from 77 (1996) to 23 (2002) - ship-ship collisions are more frequent than ship-object collisions (144 over 95)

- accident occur as frequent on fairways as in harbours

- combinations of a single barge and tug are frequently involved in accidents (60%), succeed by a combination of two barges and a tug (23%) and four barges (10%). Tank barges are involved in only 6% of the cases

- combinations with one and four barges are equally involved in accidents, but differ with respect to their type of accidents. They deal with ship-ship collisions (single barge) or ship-object (four barges). Based on a newspaper content analysis a qualitative image can be drawn from the public perception of inland shipping accidents. Although the number of accidents is relatively low, specific additional types of incidents and accident could be discriminated in the analysis:

- crew: resting and working times, sleep deprivation accidents

- vision: sailing in fog, vision limitations during manoeuvring, overtaking, course changes

- sailing process: communication and manoeuvring deficiencies, technical failures of steering equipment - fairway restrictions: grounding, collisions with locks and retractable wheelhouses with road bridges,

ship-ship collisions and cross drifting in shallow waters

- switching barges: capsizing of tugs, breaking adrift of barges, occupational accidents - damage to third parties: taking across of leisure boats.

A relative frequency of accident occurrences could not be provided due to the lack of traffic intensity data. However, it can be concluded that in view of the absolute numbers of push barges and the numbers of registered accidents, this type of shipping cannot be considered particularly hazardous. Taking into account the more favourable dimensions and vessel characteristics of the RSPS barges, the RSPS concept can be considered to be positive in comparison to regular push barges with respect to its nautical safety.

4.2 Working process analysis

Although the RSPS concept may demonstrate a favourable position in a safety assessment compared to regular push barges due to its reduced dimensions and increased robustness, a similar accident pattern may be

anticipated due to similar bottlenecks in the fairway, critical dimensions of the infrastructure, manoeuvring in the fairway at origin and destination and during switching of the barges. Such an accident pattern is related to the internal nautical safety of the RSPS concept.

In addition, the safety of the RSPS concept is also submitted to an external safety assessment, dealing with damage and consequence distances and the capacity of rescue and emergency services.

On the inland waterway section of the trip the RSPS concept may encounter disaster which is brought about from the outside due to external variables:

- the sailing process takes place in densely used waters with a relative high percentage of hazardous material transport in large volumes. Based on the Risk Map on Main Arteries, several black spots are identified along the fairway, in particular where densely populated areas are close to the fairway or dense traffic situations occur such as around Dordrecht, Nieuwe Waterweg and Hartelkanaal

- rescue and emergency services are insufficiently equipped to deal with disasters on the inland waterway arteries. Outside the Port of Rotterdam area, the timely accessibility of an accident site depends on sailing times from emergency stations and resources of local fire fighting services [20]. The ADNR regime does not take into account any involvement of public services alongside the fairway or in issuing licences for operations of maritime activities

- critical sailing conditions may occur due to extreme water heights, but an inventory of critical infrastructural assets and dense traffic situations is not yet available.

- collisions with other vessels on a crossing course in the North-South shipping lanes

- critical sea-going and wind conditions, resulting in damage or loss of barges. To this purpose the criterion of self-relianceness and damage tolerance is developed

- lashing of cargo during heavy sea conditions. Although the Marin studies indicate that the transversal stability is not critical, cargo may shift in heavy sea conditions. The hazard of damaged hazardous materials may jeopardize a timely unloading of the cargo at the port of destination.

Finally, the coupling process may indicate specific hazards unknown to other maritime activities:

- manoeuvring with barges and tugs at origin and destinations, either free sailing or not, represent a specific hazard to the RSPS concept in addition to the conventional risk of coupling barges in Duisburg by steel ropes and winches.

- the reliability and robustness of the Articouple system is well documented, but has to prove its value again in this type of combination of vessels and sailing conditions

- the combination of navigation, communication and control between barge and pusher tugs in the RSPS concept has to prove its reliability not only during the voyage, but also in the switching between sea going and inland parts of the trip on a variety of locations in the Rotterdam port area. In addition, maintenance, supply and repair facilities should be taken into account in guaranteeing the availability of the RSPS concept.

In combining the findings of the logistic simulation and safety analysis, a series of safety critical issues can be identified as input for enhanced simulations in a later phase of the project.

A small number of conceptual choices has its influence on the overall performance assessment of the RSPS. First, the availability of the logistic concept assumes that the availability of the pusher tugs is critical. However, the reliability and availability of modern tugs is extremely high, giving space to the assumption that damage to one of the barges may become the critical factor due to a considerable downtime due to accidents. A further analysis of the criticality of the overall RSPS concept is optional.

Second, the safety of switching the pusher tugs is critical. Implementation of a tug switching location in an already densely populated area with intense maritime traffic is submitted to internal-nautical as well as external environmental and rescue/emergency issues. This will limit the opportunities for a flexible adjustment of the sailing schedules and reliability of the services provided.

Thirdly, the availability of the system can be defined as a series of critical scenarios due to safety related issues: - prolonged loss of availability beyond 48 up to 72 hours. Such a downtime can be caused by flooding of a barge at sea with unintended separation from the tug pusher or collision with maritime traffic at the North Sea, a collision on the inland waterway, requiring a replacement of the barge, and heeling of the barge due to shifting cargo by heavy seas

- short loss of availability up to 6 hours, due to minor damage or collisions or fairway restrictions. While compensating for short delays, production pressure may cause a drift into unsafe situations

- an intermediate period of loss of availability between both limits causing a temporarily downtime of the system due to manoeuvring in dense traffic, at mooring stations and during switching of the pusher tugs as well as manoeuvring in restricted waters and in the vicinity of infrastructural objects or adverse weather and sailing conditions.

5. CONCLUSIONS

At the level of component safety certification with respect to crew, vessel and equipment, the nautical and technical safety is covered by existing regulations. The certification of RSPS will not encounter major safety issues due to the characteristics of the concept.

Comparison with the regular pusher barge concept, RSPS can be considered a safe and robust concept which stays within the limits of legal and formal requirements and standards of external safety, rescue and emergency management. A formal Quantitative Risk Assessment however is only possible if the concept is elaborated into more detail.

With respect to the simulation of the logistic performance, the reliability of the RSPS concept is very high. A timely departure of 99.6% and arrival of 96% can be achieved. The reliability strongly depends on the speeds, while lower than design speeds reduce the capacity of the concept considerable. Keel clearance is a critical factor and should be taken into account in view of future fluctuations of the water heights due to climate changes. Maintaining a 30 move/hour wharf crane capacity is pivotal in compensating for delays and disruptions of the working processes. Selecting a location for switching the pushers tugs in the Rotterdam area is critical due to the variance in sailing times at sea.

elaboration of the concept. The research as conducted in this project has indicated the potential for a combined safety and logistic assessment of maritime concepts, which are in an early phase of development.

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