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Time to rethink design of inland vessels?

RethinkThe Naval Architect: April 2019

According to business media reports low water levels on the Rhine in the third quarter of 2018 contributed considerably to a 1.7% slowdown of industrial production in Germany in the same period. The data provided by the Central Commission for Navigation on the Rhine (CCNR) also emphasises the impact of insufficient water depth on economics.

 

Due to low water levels in August and September 2018, the navigation on the Rhine was suspended for two periods of 30 and 15 days, respectively. Contemporary research on the impacts of climate change on transport warns that the frequency of low water periods on some of the major inland waterways could even increase in the future. Hence, the influence of long-lasting periods of extreme drought on inland navigation cannot be disregarded and should be considered when designing a vessel.

 

The modernisation of inland vessels in Europe mainly concerns the innovative solutions aimed at improvement of propulsive efficiency, the use of alternative fuels, the use of telematics and the promising opportunities for introduction of autonomous shipping on inland waterways.

 

The main particulars of the new-built vessels (which are typically divided in CEMT classes), however, do not change significantly. It could be argued that the vessels are already optimised in this respect, as the choice of the main dimensions is decisively affected by the waterway constraints, including the height of bridges, the length and breadth of locks and the fairway depth.

 

Yet studies indicate that a modification of main dimensions in comparison to the standard ones could improve vessel performance.

 

Optimised vessels for the Danube – and beyond
The state of inland navigation in the world varies from one region to another. But beyond any doubt, the Rhine basin could be considered as the most developed region in this respect in Europe. Therefore, there is a tendency to directly apply the Rhine experiences in design and operation of inland vessels elsewhere in Europe.

 

However, inland waterways may differ considerably with respect to navigational conditions, including fairway constraints and weather conditions.

 

Perhaps the most prominent difference between the Rhine and the Danube is the water depth. The Danube is characterised by the shallow-water sectors on both the Upper and Lower Danube.

 

The design draught of the so-called Large Rhine vessels (CEMT class Va, length L = 110m, beam B = 11.4m), which form the backbone of the transport on the Rhine, is typically well over 3m. On the other hand, the inventory of the bottlenecks on the Danube reveals that 2.5m draught – targeted by international agreements as the minimum that ought to be possible for most of the year – cannot be achieved in ‘dry seasons’, which could last for weeks or even months.

 

With these specific navigation conditions on the Danube in mind, the Department of Naval Architecture at the University of Belgrade conducted several studies on the design of (extremely) shallow-draught self-propelled cargo vessels. The goal of these studies was to investigate the feasibility of a shallow-draught alternative to the Large Rhine vessels, that is, a design which would fit into CEMT class Va but would enable navigation throughout the year.

The study introduced several vessels, including the E-Type vessel: a bulk carrier for the Danube with an extremely shallow design draught, d = 2m. In order to compensate for the cargo capacity lost due to the low draught, the beam was increased to B = 15m. The length of the vessel was L = 103.8m. Comparisons were made with the standard deep-draught vessels of the same class by calculating the transport costs for a range of water depths.

 

Regardless of the criterion used, the conclusions were unanimous: if the water is sufficiently deep, the shallow-draught vessels may not be as efficient as the deep-draught ones.

 

Yet in limited water depth conditions (that is in hw ≤ 3.5m), the shallow-draught vessels perform better and may attain higher speeds as well as lower transport costs. Perhaps most importantly, being climate change-resilient and less dependent on weather phenomena, they could provide continuous service throughout the year and thus improve the reliability of inland navigation.

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