Question 1

What is the Froude number?

Accepted Answer

The Froude number is defined as Fr = V/√(gL), a dimensionless speed parameter. For Fr < 0.3, displacement vessels are dominated by frictional resistance; for Fr > 0.5, wave resistance increases sharply as the vessel transitions toward planing mode. The Froude number is a fundamental design index — geometrically similar hulls at the same Froude number have equal resistance coefficients.

Question 2

What is the Holtrop-Menon method?

Accepted Answer

The Holtrop-Menon method (1982) is a ship resistance estimation method based on statistical regression of full-scale trial data. Total resistance is calculated as RT = Cf×(1+k1)×0.5ρV²S + Rw + Rapp. The form factor (1+k1) corrects for hull shape effects, and the wave resistance Rw is approximated as a polynomial function of Froude number. An accuracy of ±10–15% is expected at the preliminary design stage.

Question 3

What is the difference between effective power PE and shaft power PD?

Accepted Answer

Effective power PE = RT × V is the minimum power required to propel the hull. Shaft power PD = PE/(ηD × ηs) is the actual engine output, divided by propeller efficiency ηD (0.6–0.7) and shaft system efficiency ηs (0.97–0.99). In practice, a sea margin (15–20%) is added to determine the maximum continuous rating (MCR).

Question 4

What is a typical range for the block coefficient Cb?

Accepted Answer

Block coefficient Cb = ∇/(L×B×T) is the ratio of displaced volume to the circumscribed box. Tankers and bulk carriers are 0.78–0.85 (full-form hulls), container ships 0.60–0.70 (fine-form hulls), and high-speed ferries 0.50–0.60. A higher Cb improves cargo capacity but increases wave resistance.

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Holtrop-Menon Method