8. State about water interaction resistance and air resistance of the ship?

a. Resistance of water:

Resistance, which is generated when a ship moves on water surface, depends on ship’s speed, roughness of wetted, form and structure of ship’s hull. Resistance of water is performed by:

RN = RS + RH + RM (KG)

Where:-RS: Wave – making resistance.

          -RH: Form resistance.

          -RM: Frictional resistance.

* Wave-making resistance is made due to wave when a ship moves on water surface.

RS = CS.ρV2Ω/2(KG)

With:

-CS: Wave-making resistance coefficient.

-ρ: Kinetic viscosity of water (sea water ρ = 104.8, Fresh water ρ = 102) (Kgs2/m4)

-V: Ship’s speed    (m/s)

-Ω: Area of wetted surface  (m2)

* Form resistance is generated due to form and outside structure of ship’s hull when a ship moves on water surface.

RH = CH. ρV2Ω/2(KG)

CH: Form resistance coefficient

* Frictional resistance:

Friction resistance is generated due to roughness of ship’s hull. It is determined by:

RM = CM.ρV2Ω/2(KG)

CM: is frictional resistance coefficient. Reynolds calculated it:

CM = 0.455 lgRe (Re: Reynolds number)

b. Resistance of air:

Besides the resistance of water, air also generates resistance when a ship moves. Resistance of air is generated by air affecting on ship’s floatage. Resistance of air depends on form and section area of ship’s floatage, ship’s speed, direction and speed of the wind.

Resistance of air is performed by this equation:

RK = CK.ρk VK2FC/2  (KG)

Where:

- CK: Air resistance coefficient, it depends on floatage structure form of a ship

All of ship’s floatage have a form of pyramid: CK = 0.4-0.5

A part of ship’s floatage have a form of pyramid: CK = 0.6-0.7

Ship’s floatage have a form of a arc: CK = 0.7-0.8

Ship’s floatage have a flat form: CK = 0.8-1.0

-ρK: Density of air, ρK = 0.125 (KGs2/m4)

-FC: Transverse projected area of floatage (m2)

-VG: Relative speed of the wind (m/s)

VG = √(V2 + W2 + 2VWcosα)

-V: Ship’s speed    (m/s)

-W: Absolute speed of the wind (m/s)

-α: Angle is formed by direction of the ship and the wind.