Question

(a) What factors influence the frictional resistance of a ship and what formula is used to calculate the resistance? (6)

(b) A ship 120 m long displaces 10500 tonne and has a wetted surface area of 3000 m2. At 15 knots the shaft power is 4100 kW, propulsive coefficient 0.6 and 55% of the thrust is available to overcome frictional resistance. Calculate the shaft power required for a similar ship 140m long at the corresponding speed. f = 0.42, and n = 1.825. (10)

Answer 1

The frictional resistance of a ship depends on:

Speed of ship
Wetted surface area
Length of the ship
Roughness of hull
Density of water

According to Froud's Formula

$$R_{f}=fsv^{n}$$

where,

f = Co-efficient which depends on
- Length of ship
- Roughness of hull
- Density of water
S = Wetted surface area in m2
V = Speed of ship in knots
n = index (approx. 1.825)

The value of f for mild steel is:

$$f=0.417+\frac{0.773}{L+2.862}$$

✓ Verified Model Answer (Text Solution)

The frictional resistance of a ship depends on:

The value of f for mild steel is: