Frictional resistance arises due to the interaction between the ship's hull and the water as the vessel moves. This resistance is caused by eddying water adjacent to the hull that is drawn along with the ship. The frictional resistance is given by:

$$R_{f\:=\:}f\:.\:s\:.\:v^{n}$$

Where:

• f = Coefficient of friction
• s = Wetted surface area
• v = Ship's speed in knots
• n = Constant (1.82)

• Frictional resistance increases with increasing ship speed. The relationship is not perfectly linear, but it's approximately described by the formula Rf = fsv^n (Rf ∝ v^n), where 'n' is a constant (approximately 1.82). This means that a small increase in speed results in a larger increase in frictional resistance.

• Frictional resistance is directly proportional to the wetted surface area (Rf ∝ s). A larger wetted area (the part of the hull submerged in water) leads to greater frictional resistance. The wetted area increases with the ship's draught (depth in the water).

• Increased surface roughness increases frictional resistance. Roughness can be caused by fouling (marine growth), corrosion, or poor hull maintenance. Regular cleaning and maintenance of the hull surface help to minimise roughness and reduce resistance.

• Frictional resistance is influenced by the vessel's length. As the length increases, the wetted surface area grows, and the coefficient of friction (f) changes, leading to an increase in Rf. Longer vessels experience higher frictional resistance, but streamlined designs can mitigate the effect to some extent.