Measurements with the first installed Flex Tunnel

The results of measurements taken aboard the push-barge combination ‘Rhenus Duisburg’ fitted with the first Flex Tunnel have proven its success. DST (Development Centre for Ship Technology and Transport Systems) developed the push-barge combination at the behest of the shipping line Rhenus PartnerShip, for the shipment of coals from Rotterdam to Lünen (Germany). One of the vital basic principles was that the vessel not only has to sail with a barge linked in front, but also often has to convey two additional barges attached alongside during its passage along the Rhine. The entire convoy makes a loaden outward journey and then proceeds in flash along the Wesel-Datteln Canal. A sailing profile which is applied both while loaded and unloaded with ballast, and in deep and shallow water. The Flex Tunnel has proven its functionality with this sailing profile.

Measurements were taken both during a trial voyage and in regular service. The vessel also sailed in a range of circumstances, both loaded and unloaded, and at various speeds in each case. The functionality was subjected to extensive trials at all speeds, and the measurements taken invariably remained within the design margins, which implies that there are no restrictions on the use of Flex Tunnels at any speed whatsoever. As expected, the results confirm that extremely high vacuum levels are achieved with a deployed tunnel, which implies that the Flex Tunnel is ideally suited for use with unloaden vessels. The airtight seals on the thrusters and the hull ensure that there is sufficient water surrounding the propellers, thus avoiding any loss of output due to propellers breaching the surface of the water.

The Flex Tunnel therefore offers one the option of fitting large, 2,000 mm propellers, which improves propulsion and reduces fuel consumption as a direct result.

The initial findings, based on analysis of the measured data and comparison with vessels with conventional tunnels, suggest that the ‘Rhenus Duisburg’ achieved around 27% lower energy consumption. This high output is inextricably linked to application of the Flex Tunnel, which in turn enables optimum stern design for the afore mentioned operating area. DST not only designed the underwater hull, but also subjected it to extensive tests. The model test reports reflect the actual circumstances almost exactly, which emphasises the quality of the development institute’s model tests.

While Van der Velden Marine Systems initially expressed a cautious estimate of energy savings between 10 and 20%, the provisional results actually proved surprisingly high. The Flex Tunnel has therefore set the trend for the ship of the future.