FROUDE'S LAW OF COMPARISON
- There are three important observations given by Froude. They are:
1. For geometrically similar ships, " The speed of the ships is found to be directly related with the square root of their lengths (ie) v/√l = V/√L where, v and l are the length and speed of the ship or model, V and L are the speed and length of the ship respectively. This speed is called as corresponding speed.
2. For any two geometrically similar ships or between a ship and its model which runs at corresponding speed, their residuary resistance is directly related with the displacement (ie) Rr1 / l3 = Rr2 / L3 where, Rr1 and 2 are the residuary resistance of the model and the ship, l, L are the length of the model and the ship respectively.
3. Froude gave the formula for frictional resistance as
Rf = f S vn
where the symbols represent the following
f - coefficient depending upon the length of the surface,
S - wetted surface area of the ship in m2,
v - speed of the ship in m/s,
n = 1.825
The wetted surface area can be given by S = c√(Δl)
Where c- coefficient mostly = 0.28, Δ- Displacement in tonnes, l- length of the ship in m,