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Residual Resistance

Residual resistance R🇷 comprises wave resistance and eddy resistance. Wave resistance refers to the energy loss caused by waves created by the vessel during its propulsion through the water,
while eddy resistance refers to the loss caused by flow separation which creates eddies, particularly at the aft end of the ship.

Wave resistance at low speeds is proportional to the square of the speed, but increases much faster at higher speeds. In principle, this means that a speed barrier is imposed, so that a further increase of the ship’s propulsion power will not result in a higher speed as all the power will be converted into wave energy. The residual resistance normally represents 8-25% of the total resistance for low-speed ships and up to 40-60% for high-speed ships.

Incidentally, shallow waters can also have a great influence on the residual resistance, as the displaced water under the ship will have greater difficulty in moving aftwards.

The residual resistance is found as follows:
R🇷 = C🇷 × K

C🇷- coefficient of specific residual resistance

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