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Abstract

There is a pressing need for navies to 'go green', to meet stricter regulations, decrease dependence on volatile energy supplies, and increase ship autonomy. It is therefore desirable for the military to operate in a leaner energy fashion, minimising oil requirements as much as possible and increasing the use of domestic and renewable energy sources. Wind-assistance has seen a resurgence of academic and commercial interest recently driven by stricter regulations on atmospheric pollution from ship engines, encouraging advancements in new wind-assistance technologies. However, the power available from the wind is sporadic, and the inability for active warships to 'follow the wind' makes reliance on wind a difficult task. Considering this, additional flexibility may be offered when capturing wind energy by combining wind-assistance and energy recovery, using the propeller acting as a hydrokinetic turbine with the generated output being connected to the ship?s electrical power system. As such, during periods when the wind power exceeds the propulsion demand, the excess energy may be captured and stored. Previous research indicated a good level of reduction in fuel consumption when using wind-assistance combined with hydrokinetic energy recovery via a fixed pitch propeller. It was identified that the maximum reverse power flow for a given ship speed is closely linked to the propeller blade angle. Exploiting this fact, this study develops the concept by considering a controllable pitch propeller, offering a greater level of flexibility and potentially increasing the maximum reverse power flow which may be achieved. Torque and thrust characteristics of a propeller are estimated for a propeller in a turbine configuration using numerical methods to give an indication of potential improvements to energy recovery when using a controllable pitch propeller over a fixed pitch propeller.

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