Pulling Tanker Design into the Future

The innovative NVC-Design tanker concept first presented in 2002 by Rolls-Royce has moved forward. At the heart of the NVC-Design tanker concept are twin Ulstein Aquamaster Azipull thrusters with pulling propellers, in a compact arrangement using simple mechanical transmission from two medium speed diesel engines that also supply the electrical services and cargo pump loads. By choosing this layout, more flexibility is gained to optimise the lines of the hull for the best combination of deadweight and economy in operation. Reduced length of the engine room allows the cargo space to be 5-7 per cent larger than usual in a vessel of given overall dimensions.

Azipull units enable the design of the hull to be pushed in directions, which would probably not pay off with conventional thruster solutions. Short, beamy and full-bodied tankers can have good resistance qualities if well designed. By their very nature they are likely to have poor inherent directional stability, needing large thruster steering corrections and increased sea margins on powering if propelled by conventional pushing thrusters. On the other hand, the rudder effect of the Azipull thruster and the high side force it can generate in relation to helm angle allow the hull advantages to be retained while adding the benefits of azimuth thrusters in manoeuvring. An attraction for the shipyard is that propulsion machinery is easy to install, while the simpler aft-ship hull form helps to reduce building costs.

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