Retractable Propulsion Tunnel in the Europort 2013 Spotlight

By George Backwell at October 25, 2013 23:37
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Van der Velden Marine Systems will be highlighting a new propulsion tunnel developed specifically for inland vessels at the upcoming Europort 2013 Expo in Rotterdam: what’s different about this tunnel is that it’s completely retractable, and for very good reason.

Fixed tunnels are commonly used on inland ships to provide a proper water flow into the propellers in shallow waters, but the downside of this arrangement is that it has been found that loaded inland ships sail in deeper waters about 85% of the time, where the tunnel simply acts as a drag. The increased hull frictional resistance, due to the permanently installed tunnel, results in reduced efficiency and consequent higher fuel consumption most of the time.

Inland waterway tankship: Photo courtesy of Van der Velden

Sizing up this contradiction of purposes, Van der Velden hit on the idea of a fully retractable tunnel, turning for help in the development of the concept to the German research institute DST (Development Centre for Ship Technology and Transport Systems). The outcome of this collaboration was the patented Van der Velden® FLEX tunnel, which is embedded into the hull, and only deployed when the vessel enters shallow waters.

Van der Velden® FLEX tunnel mechanism: Image courtesy of the manufacturers

It has been found that vessels fitted with the retractable tunnel remain operational for longer than other vessels in shallow waters. In addition, the manufacturers say it is possible to optimise the hull design so that the cargo space and loading capacity are increased. Smaller propellers and rudders can be installed, reducing both weight and draught in equal measure. The FLEX Tunnel is also approximately 66% the size of a conventional tunnel, resulting in lower resistance.

Another benefit comes from the way the Van der Velden® FLEX Tunnel is mounted on the nozzle. Conventional tunnels are installed over the nozzle in order to allow for water discharges via a vent-hole between tunnel and nozzle; an arrangement that increases the length of the tunnel and causes it to stick out behind the nozzle. With the retractable tunnel this is no longer the case; the retractable tunnel is seamlessly constructed over the nozzle, stopping any false air infiltration between the nozzle and tunnel.

The manufacturers add that to ensure  optimal efficiency and thus maximise fuel savings the Van der Velden® FLEX Tunnel is designed to be combined and integrated with their DOLPHIN XR rudder and spoiler.

Van de Velden summarise the following benefits:

  • Considerable fuel saving
  • Less resistance
  • Improved manoeuvrability and velocity
  • Propulsion efficiency of about 10%
  • Increased cargo space and loading capacity




Comments (1) -

Thrustmaster of Texas, Inc. in the USA has been building retractable thrusters and combination retractable/tunnel thrusters for many years.  Prime movers can be electric for L drives or hydraulic for low profile decks if needed.  Both permit azimuth steering.  Current mechanical thrusters are available up to 2 MW and can retract as much as 3.5 meters into the hull.  Combination thrusters can serve as bow or stern thrusters in the retracted position and as azimuth thrusters in the extended position.

Charles Watson |     10/30/2013 10:37:58 AM #

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