Class 1 (Chief Engineer) Engineering Management 📅 Jun 2023

Exam Question

Viscous (frictional) resistance is a major component of overall resistance and hence an important area of attention for energy efficiency improvement of ships. Explain various skin friction reduction methods currently under consideration, with special mention on the following: (16)

(a) Hull Air Cavity systems

(b) Hull surface texturing

Reference Answer

### Introduction to Viscous (Frictional) Resistance
Viscous resistance, or skin friction, is the component of a ship's total resistance generated by the shear forces between the hull surface and the layer of water immediately in contact with it (the boundary layer). For displacement vessels operating at low to moderate speeds (e.g., tankers, bulk carriers), it can account for 70-80% of the total resistance. For high-speed vessels, it remains a significant component, often around 50%. Consequently, reducing skin friction is a primary objective for improving ship energy efficiency, directly impacting fuel consumption, operational costs, and compliance with regulations like the Energy Efficiency Existing Ship Index (EEXI) and the Energy Efficiency Design Index (EEDI).
The fundamental formula for frictional resistance is:
$$ R_f = C_f \times \frac{1}{2} \rho S V^2 $$

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