The accurate prediction of the added resistance with motions and the ship attainable speed under actual weather conditions is essential to evaluate the ship performance in realistic operation conditions, plan a safe and energy efficient voyage and assess environmental impact. Regarding the international regulations, the ship speed reduction coefficient (fw) due to wind and waves is under discussion in International Maritime Organization (IMO) to calculate Energy Efficiency Design Index (EEDI) for new ships in the representative sea conditions of wind and waves. In the present study, a reliable methodology is presented to estimate the added resistance and the ship speed loss of a container ship in specific sea conditions of wind and waves in random seas and the effect on the ship speed loss by the change of ship speed was investigated with consideration for the slow steaming.


Now more than ever, reduction of ship pollution and emissions, maximization of energy efficiency, enhancement of safety requirements and minimization of operational expenditure have been required. Traditionally, ship resistance and propulsion performance in calm water has been concentrated in the ship design stage even though there have been some changes for ship and hull form design from design draught and speed to specific range of draught and speed considering operating profile (Kim and Park, 2015). When a ship advances through a seaway, she requires additional power in comparison with the power required in calm water due to actual weather, hull fouling and other operating conditions. This degradation of the ship performance in a seaway is generally called "Sea Margin" which is the percentage of the additional power needed on top of the power required the in calm water. Sea margin is reported to be about 15-30% of the power required in calm water (Arribas, 2007), whereas a 15% sea margin most commonly applied. A more accurate prediction of the added resistance with motions and ship speed loss is essential not only to assess the sea margin to determine the engine and propeller design point, but to evaluate the ship performance and environmental impact under actual weather and operating conditions.

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