• University of Cebu - Maritime Education and Training Center

• BSMT 12A

Resistance (NA 324) 2nd Semester S.Y. 2020-2021

I. TYPES OF POWER IN SHIPS:

a. Indicated Power (Pi) – is the theoretical maximum output power of the engine. The

indicated power is the total power available from the expanding of the gases in the

cylinders negating any friction, heat loss, and entropy within the system.

b. Brake Power (Pb) – is the power produced by the ship’s prime mover. The prime

mover is the portion of the drive train that converts heat energy into rotational energy.

For most ships, the prime mover is a steam turbine, gas turbine, or diesel engine.

c. Shaft Power (Ps) – is the power delivered to the propeller shafts of the ship. It is

measured by a device called “torsionmeter”.

d. Delivered Power (Pd) – is the power delivered by the shaft to the propeller. The

amount of power delivered to the propeller will be less than shaft power because of

transmission losses in the shaft.

Pd = Pt + Propeller losses

Pd = 2πTN

e. Thrust Power (Pt) – is the power produced by the propeller.

Pt = Tf x Va

f. Effective Power (Pe) – is the power required to tow a ship.

1. Relationship Between Powers:

Pb = Pi – friction losses in engine parts

Ps = Pb – friction losses in gears and engine bearings

Pd = Ps – friction losses in shaft bearings aft of torsionmeter

Pt = Pd – propeller losses

Pe = Pt – hull losses

2. Forces:

Towing Resistance (Rt)

Thrust Force (Tf)

Thrust Deduction Fraction (F) F = Tf – Rt

Thrust Deduction Coefficient (t) t = (Tf – Rt)/T

Thrust Force Tf = 𝜌(𝜋 4 𝐷2 - 𝜋 4 𝑑2)(𝑃2𝑥𝑁2𝑥𝑅𝑆𝑅)

Where: D – outside diameter

d – inside diameter

P – Pitch

N – rotational speed

𝜌 – density (SW)