The propeller is fitted on the outboard end of the propeller shaft

It is also called as tail-end shaft or tail shaft

It passes through the Stern Tube

The outboard end of the Shaft is tapered

Propeller Boss fits on the tapered part of the Shaft

Propeller Nut is screwed on the end to lock the Propeller

**Oil Lubricated Stern Tube**

Stern Tube is made of Cast Iron

Propeller Shaft passes through the Stern Tube

Stern Tube carries the weight of the Propeller Shaft and the Propeller

Stern Tube are lined with white metal & lubricated with Oil

Both ends of the Stern tube has lip seals made of nitrile rubber.

Oil in the stern tube is maintained at a certain pressure between the lip seals

Chrome liners are provided on out board and in board ends of the Propeller Shaft

The elastic lip of the seal grips on the rubbing surface provided by chrome liners

Seals prevent the entry of seawater and also prevents the loss of lub oil

Large tanker/ships with large draught changes are fitted with two oil header tanks – one for ballast condition and another for fully loaded condition

** ****Basic Marine Engineering Book **

**Page No. 151 Fig 8.2 (a) and Page No. 152 Fig 8.2 (b)**

** **

**Types of Propellers**

- Solid Propeller (Fixed-Pitch Propeller)
- Controllable-Pitch Propeller
- Contra-Rotating Propeller
- Vertical-Axis Propeller

** Solid Propeller** (Fixed Pitch Propeller)

Blades are attached to the Boss/Hub

Blades are Helicoidal form (Skewed) [blade has a twisted appearance when viewed from tip to centre]. When Propeller is rotated – it SCREWS or THRUSTS __its way through the water by giving momentum to the column of water passing through it__. Pitch is the axial distance that a Propeller will move in one revolution. Fixed Pitch = for each revolution the axial distance moved is same

**Basic Marine Engineering Book Page No. 153 Fig 8.3**

Controllable Pitch Propeller (cpp)

Difference between CPP ( controllable ) and fixed pitch propeller.

Sl. No |
Solid / Fixed Pitch Propeller |
Controllable Pitch Propeller |

1 | Speed of Ship is controlled by varying the speed of Engine | Speed of the ship is controlled by varying the pitch of the propeller |

2 | Engine with varying speed is required | Engine with constant speed is enough |

3 | Hence Shaft driven auxiliary cannot be fitted | Hence Shaft driven auxiliary can be fitted |

4 | Astern movement of the ship is by reversing the engine {engine should be of reversing type} | Astern movement of the ship is by varying the pitch of the propeller {unidirectional engine is enough] |

5 | Full power of the engine is not available during astern running | Full power of the engine will be available during astern running also |

6 | Hence Stopping time and distance is more | Hence Stopping time and distance is less |

7 | Manoeuvring in confined water is difficult | Manoeuvring in confined water is easy |

8 | Propeller efficiency is more | Propeller efficiency is less since large diameter boss/hub is required |

9 | Cost is low | Cost is high |

10 | Cost of repair and maintenance is less | Cost of repair and maintenance is more |

**Maximum Continuous Rating (MCR) – **It is the maximum power output (kW/BHP) that an engine can produce while running continuously at safe limits and conditions

** **

** **

**Propulsion Efficiency**

Propeller Efficiency: η_{p} = __P _{t} V_{i}__

2π N T

Propulsive Efficiency: η_{t} = __R _{t} V__

** **2π N T

P_{t} = Thrust (Propeller axial thrust force)

V_{i} = Inflow Velocity (Mean inflow velocity)

N = Rotation rate (Rotational speed of the propeller) in rev/sec

T = Torque (Propeller shaft torque)

R_{t}= Total Ship resistance

V = Ship Speed (Ship velocity)

__ __

__SFOC (or) SFC: Specific Fuel Oil Consumption__** = **__Mass of fuel consumed per hour__ g/kWh

Power developed in KW

__ __

Consumption of Fuel Oil per Unit Energy at the Output Shaft of the Engine for given time [g/kWh (or) g/BHPh]

(Or)

Mass of Fuel Oil Consumed per average Shaft Power developed by the Engine for a given time

SFOC = __C _{o} D 10^{6}__

h P_{e}

10^{6} is multiplied to convert the fuel oil unit in tonnes to gram

C_{o }= Fuel Oil Consumed Over the period in m^{3 }

D = Temp. Corrected Density in kg / m^{3}

h = Measuring period in hours

P_{e} = Brake Horse Power bhp or kW

Take flow meter reading for specific time interval [usually 1 hr period, h = 1 hr) Diff between initial readings and final reading (after 1 hr) = C_{o} in m^{3 }

Density is given in Bunker Delivery Note in kg /m^{3}

Calculate Density at the Temp near the flow meter.

Temp Corrected Density D = (Density of Fuel Oil @ 15^{0}C) * [1-{(T-15) * 0.00064}] kg/m^{3}

Calculate Shaft Power (BHP/kW) at the given interval P_{e}

SFOC is used to determine the Efficiency of the Engine

** Power-to-weight ratio of engine** =

__Power generated by the engine__

Mass of the engine

Example:

Engine’s Power = 250 kW

Engine’s Mass = 380 kg

Power-to-Weight Ratio = 0.65 kW/kg

Power to Weight Ratio is used for __comparing the Performance__ of one Engine with the performance another engine.

__ __

** Pitch** is the axial distance that a Propeller will move in one revolution

__ __

P = 2 π R tan θ metres

P = __2 π R _{1} tan θ_{1} + 2 π R_{2} tan θ_{2} + ……. 2 π R_{n} tan θ_{n }__

**metres**

n

P = Pitch Ratio x Diameter of Propeller in** metres**

P = Pitch in **metres**

R = Radius from the centre of shaft to section in** metres**

θ = Pitch Angle in** degrees**

tan θ = Natural Tangents under Mathematical Tables in Science Data Book (Clark’s Tables)

** **

** **** Scientific Calculator – Select the Mode – ‘Deg’ **

** Enter the Value of θ (given in degrees)**

** Press ‘tan’ key**

** **

** Propeller Speed **(Theoretical Speed)

**(V**is the distance the propeller will move in unit time if working in an unyielding fluid

_{T})V_{T }= __P x N x 60__ ** Knots (Nautical Miles/hr)** **(nm/hr)**

1852

V_{T }= Propeller Speed (Theoretical Speed) in **Knots (Nautical Miles/hr)** **(nm/hr)**

P = Pitch in **metres**

N =Revolutions per minutes in **rpm **

** **

N x 60 = n (Revolutions –**No Units**)

Theoretical Distance = __P x n__ in** Knots** **(Nautical Miles)** **(nm/hr)**

1852

** Apparent Slip** (Percentage Slip) is the difference between the Propeller Speed (V

_{T}) and the Speed of the Ship (Actual Speed) (V) expressed as a percentage of Propeller Speed (Theoretical Speed) (V

_{T})

Apparent Slip (Percentage Slip) = __V _{T }– V__ x 100

**%**

V_{T}

V_{T }= Propeller Speed (Theoretical Speed) in **Knots (Nautical Miles/hr)** **(nm/hr)**

V = Speed of the Ship (Actual Speed)

V = Actual Distance

Time taken to cover the Distance

Apparent Slip = __Theoretical Distance – Actual Distance__ x 100 **%**

Theoretical Distance

__ __

__ __

__Wake Speed __

When a ship moves, due to the friction between hull and the water, the water around the ship also moves. This moving water is known as Wake.

Speed of moving water (Wake) is known as Wake Speed (V_{w})

V_{w = }w x V **Knots** **(Nautical Miles/hr)** **(nm/hr)**

w = 0.5 C_{b} – 0.05

w = Wake fraction

C_{b} = __Volume Displaced__

L x B x D

L = Length in **m ** B = Beam in **m** D = Draught or Draft in** m**

Volume Displaced = __ Δ __ Volume = __Mass__

1.0125 Density

__ __

Δ = Displacement in **tonnes **

__ __

__ __

** Speed of Advance **is the Propeller added Speed (Speed added by the Propeller)

__Speed of the Ship__** (Actual Speed) (V)** = Wake Speed (V_{w}) + Speed of Advance (V_{a})

** V** = V_{w} + V_{a }**Knots** **(Nautical Miles/hr)** **(nm/hr)**

** **

**Basic Marine Engineering Book Page No. 154 – Figure**

__ __

__Real Slip__** or True Slip **is the difference between the Propeller Speed (Theoretical Speed) (V

_{T}) and speed of advance (V

_{a}) expressed as a percentage of Propeller Speed (Theoretical Speed) (V

_{T})

Real Slip = __V _{T }– V_{a }__ x 100

**%**

V_{T}

__ __

__Power Estimation__

R_{t} = ρSV^{n}

S α (Length)^{2}

Δ α (Length)^{3}

S α Δ^{2/3}

R_{t} α Δ^{2/3 }V^{2}

P α R_{t }V

α Δ^{2/3 }V^{2} V

C = __Δ ^{2/3 }V^{3}__

P

R_{t }= Total Resistance of a Ship

ρ = Density of Water (kg/m^{3})

S = Wetted Surface Area (m^{2})

V = Speed (Knots)

Δ = Displacement (tonnes)

P = Propeller Power / Engine Power (kW)

Index ‘n’ is taken as ‘2’ since ships are slow or medium speed

ρ is considered constant since ships will be in sea water

C is constant known as ‘Admiralty Coefficient’

__ __

__Power Estimation__

** (A) Power = Δ^{2/3} V^{3}**

** C**

** **

** (B) Δ_{1}^{2/3} V_{1}^{3} = Δ_{2}^{2/3} V_{2}^{3}**

^{ }** P _{1 }P_{2}**

** **

**If Δ _{1 }= Δ_{2}**

_{ }

** P_{1 }_{ }= V_{1 }_{ }^{3}**

** P _{2 }V_{2}**

** **

**P = **Power of the Engine in **kW**

**Δ = **Displacement in **tonnes**

V = Speed of Ship (Actual Speed) in **Knots** **(Nautical Miles/hr)** **(nm/hr)**

**C = **Admiralty Coefficient

** **

**Δ ^{2/3} – Scientific Calculator First Take Cube Root & then Square it**

__Fuel Estimation__

- Daily Fuel Consumption
**α****Δ**^{2/3}V^{3}

^{ }**α** ** V ^{3}**

^{ }

Fuel Coefficient = ^{ }__Δ ^{2/3} V^{3}__

^{ }**Daily Fuel Consumption **

Daily Fuel Consumption = Fuel Consumption / day in **tonnes**

= Daily Consumption in **tonnes**

** **

** **

** **

** **

**Δ = **Displacement in **tonnes**

V = Speed of Ship (Actual Speed) in **Knots** **(Nautical Miles/hr)** **(nm/hr)**

** **

Voyage Consumption = Total Fuel Consumption during the Voyage in **tonnes**

** **= Total Voyage Consumption in **tonnes**

Voyage Distance = Distance Covered during the Voyage in **Knots** **(Nautical Miles/hr)** **(nm/hr)**

** **= Total Distance in **Knots** **(Nautical Miles/hr)** **(nm/hr)**

** **

** **

(2) __ Δ_{1}^{2/3} V_{1}__

^{3}=__Δ___{2}^{2/3}V_{2}^{3}** Daily Fuel Consumption _{1 }Daily Fuel Consumption_{ 2}**

_{ }

_{ }

(3) ** Daily Fuel Consumption_{1}_{ }= Δ_{1 }_{ }^{2/3}_{ }V_{1} ^{3}**

_{ }**Daily Fuel Consumption _{ 2 }Δ_{2 }V_{2 }**

(4) **Daily Fuel Consumption = Voyage Consumption **

** No. of Days on Voyage**

** **

** **

(5) **No. of Days on Voyage = Voyage Distance **

** V x 24 hrs**

(6) ** Voyage Consumption_{1}_{ }= Δ_{1 }_{ }^{2/3}_{ }V_{1 } ^{2 } Voyage Distance _{1}_{ }**

_{ }**Voyage Consumption _{ 2 }Δ_{2 }V_{2 }Voyage Distance_{ 2 }**

_{ }

_{ }

(7) **Daily Fuel Consumption** = __Voyage Consumption x V x 24 hrs__

**Voyage Distance**

__ __

(8)** Daily Fuel Consumption_{1}_{ }=_{ }V_{1 } ^{3}**

_{ }**Daily Fuel Consumption _{ 2 }V_{2 }**

__ __

__Note: __

**If Voyage distance not given assume voyage is for 24 hrs (i.e. 1 day)**

**Voyage Distance for 1 day = V x 24 hrs**

**Usually 1 ^{st} Voyage is considered for 24 hrs (or) 1 day**