BÀI GIẢNG TRANG TRÍ ĐỘNG lực (MARINE PROPULSION PLANT)

Besides this, in large power diesel engine propulsion plant, a waste recovery steam turbine can be used to drive the generator.. 1.2 Classification of Marine Propulsion Plant Depending o

CHAPTER I: NOTIONS AND CLASSIFICATION OF

MARINE PROPULSION PLANT.

(Total: 08 periods, Theory: 08 periods, practical: 00 periods)

1.1 Notions of Marine propulsion plant.

Marine propulsion plant (MPP) is a group that consists of main propulsion plant equipment and other auxiliary propulsion plant equipment to take on the action ability of ship and the life of crews on ship in every sea condition

Depending on the ability of working, that group can be divided as follows:

1.1.1 Main propulsion plant equipment.

Main propulsion plant equipment is a system of equipment that undertake speed and direction of ship They consist of following parts:

1801 the first steam ship driven by paddle wheel was appeared, with paddle wheels installed both sides of ship Paddle wheel was used on steamers until about 1850 Two kinds of propulsion equipment above have disadvantages of unwieldy and low efficiency With paddle steamers, the immersion varied with ship displacement, the wheels came out of the water when the ship rolled, so the course will be changed and they were easily damaged due to rough seas The idea to use a screw propeller on ship appears in 1680, but until

1836 the first screw propeller was applied The screw propeller has many advantages over paddle wheel Nowadays, screw propeller was used on all ship with advantage of high efficiency and safe working There are two kinds of screw propeller used in the marine propulsion plant, they are: Non controllable - pitch propeller and controllable - pitch propeller There may be one or more propellers are used in the propulsion plant according to type of ship and the installation of the propulsion plant

It supports the main propulsion plant equipment and other operations of a ship Auxiliary equipment consists of:

a Generator

Its duty is to supply electric energy for the ship to serve many different objects, such as: illuminating, loading and unloading cargoes and all other electric equipment Remember that, there must be at least two generators in the marine propulsion plant

Generators can be driven by diesel engines like in the diesel engine propulsion plant In the other hand, in the steam propulsion plant, the generators can be driven by steam engines or steam turbines Besides this, in large power diesel engine propulsion plant, a waste recovery steam turbine can be used to drive the generator

b Compressed air system

Compressed air system generates and stores compressed air with high pressure for starting and reversing the main engines, starting generator engines, cleaning parts of the engine Besides this, compressed air is also used in remote control and automatic control systems Compressed air system consists of compressors, reservoirs (air tank), non-reversible valves, relief valves, and compressed air pipes

b Ballast system

Its duty is to adjust the balance of the ship

c Fire protection system

It is easy to happen damages due to fire on the ship especially in the engine room, so protection firing should be specially concerned Fire protection system consists of: Personal fire extinguishings, carbon dioxide cylinders, foam cylinders, water fire extinguishing system, carbon dioxide fire extinguishing system, foam fire extinguishing system

d Repairing equipment, store and spare parts for replacing

1.1.4 Equipment for serving the domestic requirement.

They are equipment to undertake the living requirements of all ship's crews They consist of light system, ventilation and air conditioner system, provision refrigerator system, fresh water system, washing water sytem and so on

1.1.5 Deck's equipment

They consist of steering gear, mooring winches, cargo winches, life equipment (life boats, life rafts an

so on )

1.2 Classification of Marine Propulsion Plant

Depending on the kind of working substance used in the main engine, the marine propulsion plant can

be classified by two main types They are steam propulsion plant and diesel propulsion plant Besides these, nuclear propulsion plant can also be used

To combine main kinds of propulsion plant with driving modes, we have many different kinds of propulsion plant

1.2.1 Steam propulsion plant.

It is a kind of propulsion plant in which, generating process of mechanical power is the process of using heat energy when burning fuel to generate steam in a main boiler, and then steam expands and generates power in a steam engine or a steam turbine In the steam propulsion plant, the main propulsion plant equipment is group of boiler and steam engine or boiler and steam turbine

In 1807, the first time the steam ship Klecmong with power of 18 horses - power appeared on a river

of South America Although the ship had small power and low speed but this event had a great significance

in the ship building industry With improvement of science and technology, ship building industry manufactured many steam engines with power up to thousand horses - power In the whole of 19 century, all

of ships used the direct driving steam engine propulsion plant

Nevertheless, steam engine has still many disadvantages This type of engine has small power, low efficiency, weight and dimension is big, so cannot satisfy the high requirements of sea transport

In about years of 80 of 19 century, a Swedish engineer Guntavdo Laval made a first steam turbine with power of 5 horses - power, speed of 25000 rpm But until 1896 steam turbine applied to drive screw propeller and the steam turbine propulsion plant came

In this period, all of steam turbines were used to drive directly screw propellers, so working conditions of turbine and propeller were contradicted each other If revolution of turbine is high then its power is large, efficiency is high and weight, dimension can be reduced In the othe hand, if turbine and propeller working together then thrust efficiency of propeller is decreased because revolution of turbine is excessively higher than optimum working revolution of propeller Therefore, in direct driving steam turbine propulsion plant, turbine has large dimension and low efficiency

To operate effectively power of steam turbine, it is required to provide intermediate equipment to reduce revolution of turbine to optimum revolution range of propeller From 1910, multi - stages mechanical gears box was applied on board and the indirect driving steam turbine propulsion plant was appeared Besides this, turbine was also used to drive screw propeller in the electric driving steam turbine propulsion plant

In beginning period of 20 century, because steam engine was still used, the combinative steam engine

- steam turbine propulsion plant was used to decrease a loss of heat due to unperfected expansion of steam in

diesel engine, direct reversing The most common is low - speed diesel engine, two - stroke with cross head and used heavy fuel oil.

The direct driving diesel engine propulsion plants have disadvantages that their weight and dimension are large so they are not suitable for ships with small displacement, limited height of engine room In that case, it is necessary to provide with indirect driving diesel engine propulsion plant to drive propeller In the indirect driving diesel engine propulsion plant, a main engine is generally kind of high and medium speed diesel engine, non- - reversible Its revolution is much higher than propeller In this kind of propulsion plant, two or more main engines can be installed together to drive propeller In the other hand, only one main engine can be used to drive two or more propellers in some cases Besides of shafting, clutch and gears box should be provided between main engine and propeller The indirect driving diesel engine propulsion plants are commonly used on passenger ships, container ships, and naval ships In comparison with the direct driving diesel engine propulsion plant, this kind of propulsion plan is more complex and lower transmission efficiency

Special driving diesel engine propulsion plants are electric driving diesel engine propulsion plant and diesel engine propulsion plant with controllable - pitch propeller The same as the indirect driving diesel engine propulsion plant, a main engine is kind of high and medium speed diesel engine, non- reversible Advantage of the special driving diesel engine propulsion plant is very flexible However, it has disadvantages: system is complex, transmission efficiency is low So it commonly used for flexible ships such as: workshop ships, naval ships, passenger ships, fishing ships, rescue ships and so on

Nuclear propulsion plant is commonly used on naval ships, especially submarines But this form of power will be used more in merchant ships when oil fuels become rarely Nuclear propulsion plant uses the energy released by the decay of radioactive fuel to generate steam, and the steam is used to turn a shaft via a turbine in the conventional way

1.3 Technical characteristics of Marine propulsion plant

In a marine propulsion plant, the characteristics of the main engine have a direct effect on technique

of operation, methods of design and installation systems and equipment in the engine room According to the type of main engines, nowadays there are two main types of propulsion plant, they are diesel engine propulsion plant and steam propulsion plant (with main engine is steam turbine)

1.3.1 Technical characteristics of diesel engine propulsion plant.

- In the diesel engine propulsion plant, working substance is combustion product of air - fuel mixing formed in engine combustion chamber

- Thermal efficiency is high while specific fuel consumption is low

- Output is not continuously generated It should be provided with air and gas distributors suitable for suction and exhaust cycles of the main engine

- When working, diesel engines generate reciprocating forces and inertia moments These inertia forces and moments vibrate body of engine and ship's hull The balance of a diesel engine is depended on weight of the engine moving parts, number of cylinders and suitable arrangement of cranks

- Engine parts withstand also the forces that vary cyclically These characteristics limit an increase in power and revolution of main engine.

- Immediate pressures and tempretures in the engine combustion chamber are very high; the engine parts have to work in high temperature and friction condition so the longevity of diesel engines are reduced

- Moving rule of the pistons independ on direction of crank shaft so rotation direction of diesel engines can be easily reversed by change work order of starting mechanism In the diesel engine propulsion plant, reversing equipment can be installed on the engine to reverse directly rotation of the engine or installed

on shafting to reverse direction of propeller shaft

- In light load conditions, diesel engines are not working economically and stably

- It is flexible because of short time for starting

- Heat energy, which goes out of engine with gas together, is high; if waste heat recovery equipment

is used in the diesel engine propulsion plant then its efficiency is raised

1.3.2 Technical characteristics of steam turbine propulsion plant.

- Working substance is high-pressure steam generated in main boiler

- Output is continuous: it is the most important advantage of turbines It permits raise revolution of turbines, therefore can increase power, efficiency and reduce weight, dimension of turbines Nowadays, the modern turbines have revolution up to 15000 (rpm) or more

- Working substance flows continuously through the turbine so rotating moment, heat and mechanical load in the parts of engine are stable Therefore, turbine has a high longevity

- All moving parts of turbine are installed on a rotor, rotated with the same certain direction and speed It permits to reduce mechanical losses, raise efficiency of turbine When working, turbine doesn't generate inertia forces

- Output of turbine depends on only parameters and amount of steam that flow through turbine So turbine can generate a large power

- Turbine direction is determined by direction of steam, which acts on blades wheel of turbine With a certain blade wheel, turbine cannot reverse its self To reverse direction of ship, it should be provided with astern turbine So it increases power loss of system Nowadays, that problem has been solved with using intermediate driving or controllable - pitch propeller

- Turbine's revolution is much higher than optimum range of propeller's revolution, so turbine cannot directly drive propeller Therefore, it should be provided with reducing gears in the system In fact, the steam turbine propulsion plant is only installed on ships with a big displacement

- Gas temperature in boiler combustion chamber is limited by heat durability of material Cycle temperature is low; boiler and transmission pipes have heat losses so efficiency of propulsion plant is low

1.4 Interaction between Hull and Propeller.

- RN (KG): Resistance of water acts on ship's hull.

- RK (KG): Resistance of air affects on floatage of ship.

a Resistance of water

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

M H S

- CS : Wave - making resistance coefficient.

- ρ: Kinetic viscosity of water (KGs2/m4)

Seawater: ρ = 104.8Fresh water: ρ = 102

- 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:

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:

2

2

C G K K K

F V C

Where:

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

All of ship's floatage have a form of a pyramid: CK = 0.4 ÷ 0.5

A part of ship's floatage have a form of a pyramid: CK = 0.6 ÷ 0.7Ship’s floatage have a form of a arc: CK = 0.7 ÷ 0.8Ship’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)

αcos.2

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

1.4.2 Relationship between main engine power and resistance of ship's hull.

We consider that effective thrust force (generated by propeller when a ship moves) is T (KG), in

balance moving condition, we have:

R

To maintain ship's speed at V (m/s) with resistance R (KG), necessary power can be determined:

P P P

V T

In fact, the propeller is now working in water, which has been disturbed by the passage of the hull, and in general the water around the stern has acquired a forward motion in the same direction as the ship This forward-moving water is called the wake, and one of the results of the wake influence is that the propeller's speed is not the same with speed of the ship The difference between ship and propeller's speed is

called wake speed VW.

w= −However, Froude expression is used only in older published data, particularly British

According to Taylor definition, wake coefficient w is the ratio between wake speed and ship's speed:

w= − P

- For one propeller-ship: w = 0.5 δ - 0.1

- For two propellers-ship: w = 0.5 δ - 0.16

(δ: Fat coefficient of the ship)

Then, propeller's speed is that:

P

P − = is called thrust-deduction fraction The thrust-deduction fraction t is determined

by practical formula of Kenvil:

t = C 1 w.

C 1 : coefficient depends on rudder structure characteristic C 1 = 0.5 ÷ 1.05

We can perform:

T t

Then:

W V t R

RV V

T

TV V

T

TV N

N

P P P P P

K H

N N

η

H P

RV N

η75

Then, power on propeller hub:

P

P CV

N N

η

With ηP is efficiency of propeller, for:

- Non-controllable pitch propeller: ηP = 0.6 ÷ 0.75

- Controllable - pitch propeller: ηP = 0.58 ÷ 0.65

When driving propeller, a part power output of a main engine is lost to overcome friction resistance

on shaft bearings, clutch, and reducing gears box So the power of a main engine depends on also shafting efficiency ηtr :

tr P H tr

CV e

RV N

N

ηηη

η = 75

Shafting efficiency depends on characteristics of propulsion plant:

- Direct driving propulsion plant: ηtr = 0.95 ÷ 0.98

- For indirect driving propulsion plant, shafting efficiency ηtr still depends on efficiency of clutch and reducing gears box and its value is about 0.86 ÷ 0.96

In fact, the power of a main engine Ne determined above equals to only 85% its designed power.

In fact, to meet all these requirements together is very difficult To simplify it, we study the following requirements;

1.5.1 Requirement about the power of marine propulsion plant according to propeller and hull characteristics.

Suppose NK (hp) is the necessary power to maintain ship's speed at V (m/s), with total resistance R

N N

η

The power on propeller hub:

P H P

P CV

RV N

N

ηη

η =75

Power of the main engine:

tr P H tr

CV e

RV N

N

ηηη

η = 75

Power of the main engine depends on type, functions and displacement of the ship If the ships have the same displacement, but functions and types are different then their powers are also different Therefore, definition "relative power" is used:

The power on the propeller hub NCV is determined according to 1.4 However, to simplify the power

on the propeller hub can be calculated by Naval formula:

w CV

C

D V

2 3

This result shows that at the same displacement, the higher the speed, the larger power is.

1.5.2 Requirement about economical norm of marine propulsion plant.

The economical norm in operating of marine propulsion plant is estimated by amount of fuel consumption of a main engine on one knot of itinerary:

t V

- t: Working time of propulsion plant (h)

- B: The fuel consumption of main engine in the working time t (h) It can be determined:

t N g

t N g

M

1.5.3 Requirements of propulsion plant for independent working ability of the ship.

a Requirement about the weight of propulsion plant

Total weight or displacement of the ship consists of four main components:

- Weight of hull

- Weight of propulsion plant

- Weight of needments (fuel, lubricating oil, water, provision, stores and spares)

- Weight of cargoes

With a certain ship, one of the weights increases, then other component has to reduce If the weight of propulsion plant is increased then the cargoes transportation and the independent working ability of the ship

is reduced So application methods to reduce the weight of propulsion plant are necessary

In fact, the ships have the same displacement but speed and power are varied, so then the weight of propulsion plant is varied In the other hand, with the same power but the weight of propulsion plant is also varied when type of propulsion plant is different Therefore, the definition of "relative weight" is used:

W

- Area saturated coefficient of the engine room: The number of horsepower (hp) of the propulsion plant on unit of the engine room area.

S

N

- Volume saturated coefficient of the engine room: The number of horsepower of the propulsion plant

in unit of the engine room space

- ∑Ne: Total power of the propulsion plant. (hp)

- S: Total area of the engine room floors. (m2)

- V: Total volume of the engine room space. (m3)

c Requirement about the needments of the propulsion plant

Needments stored on the ship to permit her running in a certain time For the marine propulsion plant, main needment is fuel The more amount of fuel stored on the ship, the higher the independent working ability is However, weight of the fuel stored is also component of the displacement, if the fuel stored is too much then transportation ability of the ship will be reduced So the fuel stored should be calculated suitably with power, specific fuel consumption of the propulsion plant, the times on voyage, operation area of the ship

to raise the transportation ability

The fuel stored can be calculated according to the fuel consumption in all times of an independent voyage:

t g N

B e tb

Where:

- ∑B: Amount of the fuel consumption in all times of the voyage (kg)

- ∑Ne: Total power of the propulsion plant. (hp)

- gtb: Average specific fuel consumption of the propulsion plant (kg/hp.h)

- t: The times of the independent voyage (h)

d Requirement of the propulsion plant according to sea condition

- All of the machinery should normally work when the ship heeling or rolling

- All of the service system (fuel oil sys., lubricating oil sys., cooling sys., ) should normally work in every condition

- The starting, reverse and adjustment the main engine is easy in every condition The main engine has to work stably even when the ship is reversing

- It is necessary to provide the main engine with over speed protector

- The main engine can be overloaded to overcome augment resistance in some special cases

- It is easy to operate, maintain, and repair

CHAPTER 2: SHAFTING AND ITS COMPONENTS

(Total: 14.5 periods, Theory: 10.5 periods, Practice: 4.0 periods)

2.1 Arrangement of shafting.

2.1.1 Arrangement of the single shafting

Description of single shafting is illustrated in Figure 2.1

Figure 2.1: Shafting arrangement

1- E/R bulkhead 2- Stern tube 3- Water tank 4- Propeller shaft 5- Intermediate shaft

6- Intermediate bearing 7- Thrust shaft

8- Thrust bearing 9- Double bottom tank

2.1.2 Installation principle of the shafting.

There is one or more shaft line depending on kind of ships In almost cargo ships, the shafting has only one propeller and one shaft line is used Normally, a shaft line is placed parallelly with the keel of the ship; in some case the shaft line is placed unparallelly with the keel It makes with basic line an angle α, α ≤

5o (α- angle is formed by the shaft line and the keel of the ship in vertical section)

M/e3

2

1

9

In a propulsion plant with two shaft lines, they are normally installed symmetrically and parallelly to the vertical keel section of the ship In some cases, they make with the vertical keel section angles β (β- angle

is formed by the shaft line and the ship vertical keel section), β ≤ 3o If α > 5o, β > 3o then thrust force of propeller will be decreased However, in some special cases α is permitted till 15o

To reduce cost and total weight of the propulsion plant; to economize on metal and increase transmission efficiency, the shafting should be shortened

2.1.3 Position of shaft bearings.

Shaft bearings are usually positioned near bulkhead or keel of the ship where ship's hull structure is strongest Position of the shaft bearings relates to vibration of the shafting

According to the rule of Russia Register:

12D < L < 22DWhere: D - Diameter of a shaft

L - Distance between shaft bearings

If D < 100 mm, L is calculated:

3 2 max 91 D

2.2 Propeller shaft (Tail shaft)

Propeller shaft works in hard condition such as contacting with seawater and heavy load, wearing by friction so, it is required a high quality material and structure

Traditionally, a non-controllable pitch propeller is fitted to the propeller shaft with key and taper On the other hand, a controllable pitch propeller is normally fitted to a flanged propeller shaft because the operating mechanism is housed in the propeller boss Of course, a non-controllable pitch propeller could be flange-mounted, however the propeller shaft cannot be drawn into the ship for inspecting and result in a larger boss diameter of the propeller

Figure 2.2: Structure of the propeller shaft and the propeller boss

Taper Key

Shaft

The propeller is pushed tightly to taper by hydraulic jack, after that the propeller is secured to the propeller shaft by key and nut together with interference fit method

The propeller shaft is connected to the intermediate shaft by flange or coupling This flange may be cast either integral with the shaft or separately and secured to the shaft by key and nut

In some cases, especially the propeller shaft lubricated by water, to increase longevity of the shaft, a brass sleeve is inserted to the shaft The thickness of a brass sleeve is calculated as the following formula:

32

235+

1

2

34

5

67

8

911

12

2.4 Stern bearings

The propeller shaft is supported by stern bearings There is one or more bearing for each of the propeller shaft depending on the structure of the ship and length of the propeller shaft Stern bearings withstand too heavy working conditions; it is very difficult to inspect and repair (unless on dry dock) So its structure must be strong enough to ensure safe operation of the ship

There are some kinds of materials for making stern bearings such as:

- Special wood (lignum vitae)

The staves with against the grain are used in lower part of the bearing They have a higher longevity than staves with the grain These staves are closely placed and secured by brass plate The length of secured plate is equal to length of the staves and thickness of this plate is about 60% of the staves Two or three brass plates can be used to secure the staves When the bearing is working with water-cooling, the staves will expand boundary and create pressing force to each other

The metal bushes in which the staves are mounted are pressed into cast iron stern tube At the after end of the metal bush is provided with a shoulder and it is secured by a lock nut on the stern tube Generally, two staves bush are fitted in the stern tube The aftermost bush has a length about 4 times the diameter of the shaft and it is the main bearing unit The forward bush is short and acts mainly as a guide The center (unbushed part) of the stern tube is connected to a seawater service line, which, together with ingress of water between the shaft and aft bush, provides lubrication

To increase longevity of the propeller shaft, the brass sleeves must be fitted

Figure 2.4: Lignum vitae bearing

1- Metal bush 3- Secured plate 2- Lignum vitae 4- Screw

b Advantages of lignum vitae bearing

- This kind of bearing is very suitable for propeller shaft, which has a big diameter and low speed

- It is safe in operation

- Absorb vibration of the propeller shaft

- Maintain clearance between shaft and bearing if optimum cooling and lubricating

- Longevity is high (about 10 years)

There are some differences in structure of synthetic rubber bearings but basically, the rubber staves are positioned in a metal bush A groove is made between two staves to let water flow in for lubricating The metal bush is fixed to the stern tube by screws (metal bush must not rotate) The same with special wood, brass sleeves must be inserted to propeller shaft in case of rubber bearing The friction coefficient between rubber bearing and brass sleeves in water is about 0.02 ÷ 0.007 depends on kinds and shapes of rubber bearing.

b Advantage of rubber bearing

- When working in water, friction coefficient is decreased

- Abrasion resistance ability is high even in dirty water with much sludge and sand

- Noise and vibration is reduced When rotating propeller shaft can center it self

- It is cheaper than lignum vitae material

- This kind of bearing is suitable for propeller shaft with medium and high speed

c Disadvantages

- Heat exchange coefficient is low, so working temperature of the bearing is limited under 65oC If temperature is excessive the limit value about 200C, rubber may be deformed and if temperature is too low (about - 40oC), it will be hardened

- Sulfur in rubber will corrode the brass sleeve of the shaft Because of this when the ship staying in port for a long time, sometimes the shaft must be turned

- Oil must be away from bearing if not, bearing will be worn very fast

2.4.3 White metal bearing.

a Structure

A typical analysis of white metal is 3% copper, 7.5% antimony the remain is tin The thickness depends on requirement of registry Lloyd’s register recommends the thickness of 3.8 mm for shaft 300 diameters, up to 7.4 mm for shaft 900 diameters The bearing clearance can be calculated:

Figure 2.6: White metal bearing

12

34

5

1- Propeller shaft 3- White metal 5- Oil groov

2- Stern tube 4- White metal liners

D1 = 1.001D + 0.5 (mm)

Where: D1 - Inside diameter of the bearing, D - Outside diameter of the shaft

White metal liner must be fixed to the stern tube otherwise it will be turned together with shaft and be soon damaged The white metal bearing must be lubricated by lubricating oil

b Advantages of white metal bearing

- Propeller shaft without brass sleeve can be used

- It can withstand heavy load with vibration and changing direction of the shaft

- Corrosion of the shaft is prevented because seawater does not contact with the shaft

- Wear of the shaft is very small If it is properly lubricated, longevity of the bearing may last 7- 8 years

- Because there are many good features, so nowadays almost big ships use white- metal bearing

c Disadvantages

- Replacing and making is complex

- Sealing and lubricating system for propeller shaft is complex

- Longevity of bearing depends on operating condition, installation standards and especially the sealing

2.5 Stern tube sealing:

Its function is to prevent leakage of seawater through, or loss of oil from, the stern bearings Shaft seals are very important during operation of the shafting; they maintain good condition of the stern bearings and protecting marine pollution

Nowadays, there are two common types of shaft seal are used widely on board ships They are gland packing and simplex shaft seal types

2.5.1 Gland packing seal type.

Gland packing seal almost used on small ships Its structure consists of simple stuffing boxes filled with packing material; usually rove cotton imbrued with tallow or graphite as a lubricant In the case of high duty packing the material may be white metal clad Figure 2.7 below illustrates structure of a gland packing seal Gland packing can be lubricated by water or lubricating oil Gland packings are adjusted by tightening

or loosening gland cover (4)

Figure 2.7: Structure of gland packing seal

1- Propeller shaft 4- Gland cover 2- Stern tube 5- Metal bush 3- Gland packings

2.5.2 Simplex shaft seal:

a Aft seal

Figure 2.8 is an illustration of aft simplex shaft seal The aft seal is composed of the casing fixed to the hull and the liner, which is fixed to the propeller boss and rotates with the propeller shaft together The casing consists of three kinds of metal rings (flange ring, intermediate rings and cover ring), which are separately tightened with bolts Individually assembled between these rings, four sealing rings are composed the leading edge (lips) touching the liner These lips are pressed hard against the rotating liner by the water and oil pressure, elasticity of the rubber material and the tightening force of the springs to maintain sealing effect

The four sealing rings are numbered by No.1, No.2, No.3, and No.3S from the seawater side Seawater penetration is tightly protected by No.1 and No.2 sealing rings

No.1 sealing ring, in particular, has an additional function to protect the inside of the stern tube from extraneous substances in seawater

The oil pressure in the chamber between two (No.3 and No.3S) sealing rings located at forward is usually adjusted to be the same pressure as stern tube pressure, which is 0.2 - 0.3 kg/cm2 higher than sea water pressure Therefore, there is no pressure loaded on No.3S sealing ring on the above conditions Normally, lubricating oil in the stern tube is sealed by No.3 sealing ring

However, if much oil leakage from No.3 and No.3S chamber would be found, No.3S sealing ring could be used to protect the above leakage instead of No.3 sealing ring by the easy valve operation handle inboard

1

2

5

Figure 2.8: Aft simplex seal

1- Cover ring

2- Sealing ring (No.1, 2, 3, 3S)

3- Inter mediate rings

4- Oil inlet

5- Flange ring

6- Packing 7- Stern tube 8- Stern frame 9- “O” ring 10- Aft chrome steel liner

b Forward seal

The forward seal is of a construction almost similar to the aft seal, except that it is composed of two sealing rings

The sealing rings are numbered No.4 and No.5 from the side of stern tube

No.4 sealing ring seals tight the lubricating oil inside the stern tube while No.5 sealing ring seals tight the lubricating oil in the oil chamber between No.4 and No.5 sealing rings The forward liner is tightened with bolts to the split - type clamp ring mounted to the propeller shaft

Propeller boss

No.3 No.3S Propeller shaft

No 2 No.1

Figure 2.9: Forward simplex seal

1- Clamp ring 2- Forward chrome steel liner 3- “O” ring

4- Cover ring 5- Sealing ring (No.4, 5)

6- Intermediate ring 7- Flange ring 8- Packing 9- Stern tube 10- Aft bulkhead

2.6 Requirements for cooling and lubricating stern bearing.

To lubricate and cool the stern bearings, lubricating oil or water can be used If the bearings are lacked lubricating, dry friction will be created and the shaft and the bearings will be damaged soon

- For the bearings made from white metal, ball bearing, lubricating oil is used to lubricate

- Lignum vitae, rubber used water for lubricating

2.6.1 For the bearings lubricated and cooled by water.

Lignum vitae, synthetic rubber bearing uses water for lubricating and cooling Seawater outside the ship or water pumped from engine room can be used for these purposes

These kinds of the bearings need enough capacity of water for lubricating and cooling If lack of water, the bearings temperature increases then the bearings and shaft sleeve will be damaged The best temperature for lignum vitae bearing is smaller than 50oC

For synthetic rubber bearing, when lack of water the friction coefficient of the bearing increases then bearing temperature will be fast increased and both shaft and bearing will be stuck to each other

The best water for lubricating and cooling is the pressured water pumped from the engine room after cleaned by a strainer The flow of pressured water will clean sand and dirt from working surface of bearings when the ship sailing at shallow and dirty water area

Propeller shaft

No.5 No.4

12

45

6710

38

9

The water lines must be provided with pressure gauges, sight glasses, thermometer to monitor the lubricating and cooling condition of the bearings Water pressure ≤ 2.5 Kg/cm2, temperature ≥ 20oC

Cooling and lubricating water for the bearings must be supplied before trying the main engine

2.6.2 For the bearings lubricated and cooled by lubricating oil.

Oil for lubricating of this type can be supplied by a pump or a gravity tank After lubricating the bearing, the oil must be cooled by water in a cooler Pressure gauges, sight glasses, thermometer must be provided to monitor the lubricating condition

If the gravity tank is used for lubricating, they must be installed above the highest water level of the ship Level gauge and low-level alarm must be fixed to this tank

For this type of the lubricating, the sealing condition is very important if the after sealing ring damaged, oil may be leaked or seawater may come into lubricating oil, so attention must be paid when operating The best way is to follow instruction of the maker

Figure 2.10 illustrates a stern tube lubricating oil system

Figure 2.10: Stern bearing lubricating oil system

2.7 Intermediate shaft and bearing:

Depending on arrangement of engine room, marine propulsion plant may have intermediate shaft or not If engine room is arranged in midship, the shaft line may have two or more intermediate shaft, but almost ship engine room is placed at the aft of the ship and there is only one intermediate shaft Steel is material to make the intermediate shaft

- Flanges are arranged at the both ends of the shaft to connect the intermediate shaft to the propeller shaft and the thrust shaft

- Normally, each intermediate shaft has one bearing Figure 2.12 illustrates structure of the intermediate bearing Oil is used to lubricate for the bearing White metal is material to make the bearing When operating, attention must be paid to the bearing such as oil temperature, oil level, oil quality, and condition of sealing ring

(See Figure 2.12)

2.8 Thrust shaft and thrust bearing:

2.8.1.Thrust shaft:

The thrust shaft is installed between of crankshaft and intermediate shaft and together with this shaft;

it transmits power of the main engine to the propeller Thrust shaft made of forged steel, has one or two

Transfer line

Gravity tank low

Gravity tank high

Stern tube cooling tank

Venting pipe

Three-way cock

T P

Needle valve

collars In medium or high-speed engines, it is installed in the reduction gear, which is located in the after part of the main engine

2.8.2 Thrust bearing:

Thrust bearing is designed to absorb thrust force from the propeller and transmits it to the hull of the ship There are three kinds of thrust shaft bearing corresponding to the thrust shafts, these are:

- Thrust shaft with tapered roller bearing

- Thrust shaft with one collar

- Thrust shaft with two or more collars

a Tapered roller bearing

A tapered roller bearing is normally installed on small ships in a reduction gear This kind of bearing has light weigh, small size and small friction coefficient, but for the big ships it is difficult to inspect, repair and change the roller bearing

Figure 2.11: Structure of thrust shaft bearing

Figure 2.12: Structure of intermediate bearing

b Thrust bearing (with multi- collars thrust shaft):

This is a traditional type used in the past such as old steam ship Because one collar could not withstand heavy thrush force from the propeller so two, three or more collars are provided to transmit thrush force to bearings, which are fixed tightly to hull of the ship Because big size in structure and difficulty in repairing so it is rarely used nowaday

c Thrust bearing (with one collar thrust shaft)

Due to dimension of the thrust with many collars is so large, so the change in design of thrust bearing was developed with one collar thrust bearing Its structure is shown in the Figure 2.11 When shaft rotating, between surface of the collar and surface of the pad creates an oil wedge Because of that, the oil firm is always maintained between two surfaces and this kind of bearing can withstand heavy thrush force

When shaft working, L.O temperature is increased To maintain the temperature in the bearing case lower 700 C, a L.O cooler must be fitted Besides that, a heater also is installed to reduce viscosity of L.O in cold weather

2.8.3 Effect of a worn-out thrust bearing.

Misalignment of the thrust shaft system, a too small space between the collar and its bearing or a shortage of oil in the quantity may result in heating up and wearing out With a worn-out thrust bearing, the crankshaft will be approached forward in ahead turning and afterward in astern turning, thus cause the following problems:

- Heat will be produced by friction between webs and the crank pin metals or the side face of the main bearings

- Slant movements of the piston will increase wears of the piston and the cylinder liner in fore and aft direction The misalignment of the connecting rod will increase the temperature of the piston pin and crank pin metal

CHAPTER 3: MODE OF DRIVING AND DRIVING MECHANISM

(Total: 15.5 periods, Theory: 9.5 periods, Practice: 6.0 periods)

3.1 Function and classification:

3.1.1 Driving equipment and its function

Definition: Driving equipment is used to transmit power from the main engine to the propeller.Driving equipment consists of:

- Shafting: Intermediate shaft, thrust shaft and propeller shaft

- Bearings: Intermediate bearings, thrust bearing and stern bearings

- Shaft coupling

- Clutch, reduction gear (intermediate equipment)

- Electric transmission equipment

3.1.2 Classification

Today, there are three kinds of driving modes for ships They are:

- Direct driving mode

- Indirect driving mode

- Special driving mode

3.2 Direct driving mode.

3.2.1 Feature

- There is not any intermediate equipment between the main engine and the propeller Direct driving

is carried out only by the shafting

- Revolution of the propeller is the same main engine revolution

- It is commonly applied on the large and medium-sized ships when revolution of main engine is about 85 ÷ 300 rpm

- In a direct driving propulsion plant, the main engine is a kind of low-speed, large power, direct reversing diesel engine The most common is low-speed; two- strokes cycle diesel engine with crosshead

3.2.2 Advantages

- Driving efficiency is high A direct driving propulsion plant with short shafting will have a driving efficiency of about 97 - 98%

- The main engine has low specific fuel consumption New diesel engine have SFC= 120g/hp.h

- The propeller efficiency is high (because revolution of the main engine is the same as the optimum range of the propeller revolution, optimum range abt 80 -150 rpm)

- Its structure is simple and easy to maintain It is safe in working, reduces noise and vibration and has high longevity

3.2.3 Disadvantages

- The main engine has large dimensions and weight so dimensions and weight of the propulsion plant are increased, therefore transportation ability of the ship is reduced The direct driving mode is not suitable for ships with small displacement, or height of the engine room is limited.

- To reverse rotating direction of the propeller, the main engine must be reversed so it is not flexible.The direct driving mode is suitable for tanker ships, general cargo ships or bulk carriers

3.3 Indirect driving mode.

3.3.1 Feature

- There is intermediate equipment between the main engine and the propeller to transmit power Intermediate equipment may be clutch (friction clutch, hydraulic clutch) or clutch and speed reducer (hydraulic speed reducer, reduction gear)

- Revolution of the main engine is much higher than the optimum range of the propeller revolution (in some cases, revolution of the main engine and the propeller are the same)

Ratio between revolution of the main engine and the propeller is called transmission ratio:

p

n

n

i=n: Revolution of the main engine

np: Revolution of the propeller

Transmission ratio may be constant (one-stage reduction gear) or variable (multi-stage reduction gear) In fact, the multi-stage reduction gear is generally used (normally two stage for ahead and one stage for astern)

- In the indirect driving mode, the main engine is usually a high or medium-speed, four-stroke cycle, non-reversible diesel engine In some special case such as LNG or air craft carrier, steam turbine is used

3.3.2 Advantages

- Dimension and weight of the propulsion plant are small, so it reduces dimensions of the engine room and increases the cargo transportation ability of the ship At the same power, the weight of the high or medium-speed diesel engine is about 40% lighter than a low-speed diesel engine

- The same type of diesel engine can be used for many kinds of ships that have different propeller revolution rates

- It is not necessary to directly reverse the main engine for reversing direction of the ship This can be done by the multi-stage reduction gear and therefore, the flexibility of the propulsion plant and longevity of

The indirect driving mode is more suitable for the ship which requires high flexibility such as naval ships, passenger ships and container ships.

3.4 Special driving mode.

3.4.1 Electric driving.

3.4.1.1 Feature

- There is not mechanical connection between the main engine and the propeller

- There are two times of energy transformation

3.4.1.2 Electric driving diagram

This is the simplest illustration of the direct current electric driving propulsion plant

Figure 3.1 Direct current electric driving propulsion plant

1- Electric Motor 2- Excited coil of the motor 3- Excited coil of the generator

4- Generator 5- Main engine 6- Rheostat

Generator (4) is driven by the main engine (5) to supply a direct current to the direct current motor (1) The excited coil (2) of the motor is connected to the direct current grid The excited coil (3) of the generator is connected to the direct current grid through a rheostat (6) therefore the value of the current can

be changed

To change revolution of the motor, the magnetic flux of the excited coil (2) must be changed Besides this, there can change the voltage of the motor to change its revolution This can be carried out by the rheostat

To change direction of the motor, the direction of excited current must be changed

In fact the system is very complex and an alternative current electric driving system can be used

3.4.1.3 Advantages

- The same as the indirect driving mode, the main engine is usually a high or medium-speed therefore, the dimension and weight of the propulsion plant is small and thus reduces the dimensions of the engine room

- It is not necessary to reverse the main engine when altering moving direction of the ship This can

be carried out by reversing rotating direction of the electric motor Therefore the longevity of the main engine and the flexibility of the propulsion plant will be increased

+

_+

MEG

M

_-

_-

1

6

- Revolution of the propeller can be changed while the main engine is still working at a constant speed This can be done by changing revolution of the motor Therefore the main engine can always be run at the most economic region.

- It is not necessary to have a long shafting and many intermediate bearings, so the main engine can

be located in the most suitable position in the engine room

- When the ship is stable sailing on the sea, the main generator can satisfy a part of the electric energy requirements of the ship

3.4.1.4 Disadvantages

- Transmission efficiency is much lower than the two kinds of driving mode listed above

- Overload ability of the electric motor is less than diesel

- It is complex, uneconomic and expensive

- Longevity is shorter than mechanical connection

Electric driving mode is more suitable for naval ships, fishing ships

3.4.2 Controllable-Pitch Propeller Driving.

3.4.2.1 Structure and methods for controlling pitch of the propeller.

a Structure

It consists of two main parts:

- Blades can be turned around their axis

- Mechanism for controlling pitch of the propeller This mechanism is generally installed inside the propeller hub

b Methods for controlling pitch of the propeller

To vary pitch of the propeller, its blades must be turned around their vertical axis This movement is carried out by hydraulic or mechanical means Today, there are four common methods to control pitch of the propeller; the illustrations are showed as below

Figure 3.2: Methods for controlling pitch of the propeller

1- Gearing type 2- Turning type

3- Connecting rod type 4- Rack-and-pinion type

3.4.2.3 Disadvantage

- Mechanism of pitch control is complicated The quality of sealing equippment of the propeller hub

is required Therefore, it is very difficult to manufacture, assemble and repair

- Cost of controllable pitch propeller is high

- It is difficult to operate, especially determining the suitable working point between the main engine and the propeller

If the pitch ratio (H/D) and the propeller revolution (np) are selected unsuitably, the result power of the main engine and efficiency of the propulsion plant is reduced

- Knowledge of the operator is required

The using of controllable-pitch propeller driving mode becomes more suitable on naval ships, passenger ships, and workshop ships, fishing ships, rescue ships

3.5 Hydraulic driving equipment

3.5.1 Principle and Application

3.5.1.1 Principle of hydraulic driving equipment

In a hydraulic driving, the main equipment consists of a centrifugal pump and a hydraulic turbine (Figure 3.3)

A centrifugal pump (1) is installed on shaft of the main engine; a hydraulic turbine (2) with its axis is connected to the propeller shaft When the main engine is working, liquid from tank (6) will fill up the centrifugal pump and supplied to the hydraulic line (3) with high kinetic energy The liquid is then ejected

34

21

with high velocity into the hydraulic turbine Therefore, the hydraulic turbine is turned and drives the propeller shaft Liquid going out of the turbine is returned to the tank and makes a circulating circuit.

Figure 3.3: Hydraulic driving

1- Centrifugal pump 4- Return line 2- Hydraulic turbine 6- Tank 3- Hydraulic line 6- Suction pipe 4-Nozzle

Thus mechanical energy of the main engine is transmitted to the propeller by the hydraulic mechanism and working liquid

3.5.1.2 Features and application of hydraulic driving equipment

- Clutch and unclutch crankshaft of the main engine and the propeller shaft

- Extend working region of the propulsion plant The main engine will not be overloaded in rough sea conditions

- It permits a centering error between the crankshaft and the propeller shaft

- Reversible hydraulic driving equipment can be used

- Hydraulic-driving equipment is applied in the propulsion plant as a hydraulic clutch or a hydraulic speed reducer

21

3

7

564

When filling up the hydraulic clutch with liquid, the liquid with high kinetic energy is supplied by the pump into the hydraulic turbine, thus turbine revolves and drives the propeller shaft So the torque generated

by the main engine is transmitted to the propeller shaft and drives the propeller

To stop the propeller shaft, the liquid inside the hydraulic clutch is drained out, the pump is freely turned again, and the turbine is stopped

Figure 3.4: Hydraulic clutch

1- Centrifugal pump 4- Actuating shaft 2- Hydraulic turbine 5- Receiving shaft 3- Cover

b Features

- When the hydraulic clutch is working stably, torque on the receiving shaft is not changed

- Centrifugal pump and hydraulic turbine have the same dimension

- High transmission efficiency

c Transmission efficiency of the hydraulic clutch

When working, the clutch generates hydraulic loss; so a little part of the main engine power is lost That energy is transformed into heat therefore raising the temperature of the liquid The loss of power is performed by transmission efficiency of the hydraulic clutch:

2 2 1

n M N

N

Where: N1, M1 - Power, torque on the pump shaft

N2 , M2 - Power, torque on the turbine shaft

n 1 , n 2 - Revolutions of the pump shaft and the turbine shaft

2

4

5

When the hydraulic clutch is working, the revolutions of the pump and the turbine are not same, it creates a slip:

LH

n

n n

S = − =1−η

1

2 1

(%)

In fact S is about (2 ÷ 4)%

3.5.2.2 Hydraulic speed reducer.

a Principle of the hydraulic speed reducer

Hydraulic speed reducer consists of the centrifugal pump (1), hydraulic turbine (2) and nozzle (3) The pump shaft is connected to the shaft of the main engine The turbine shaft is connected to the propeller shaft The nozzle is fixed to the cover of the hydraulic speed reducer

Figure 3.5: Hydraulic speed reducer

1- Centrifugal pump 4- Pump shaft (actuating shaft) 2- Hydraulic turbine 5- Turbine shaft (receiving shaft) 3- Nozzle ring 6- Cover

The hydraulic speed reducer uses the same principle as the hydraulic clutch However, different from the hydraulic clutch, the hydraulic speed reducer has a nozzle to change velocity and direction of the liquid current inside the equipment By using the nozzle ring and difference diameter of pump’ impeller and turbine’ impeller, so revolution and torque on the turbine shaft are changed in comparison with the pump shaft

b Features

36

25

1

4

- There is a nozzle ring to change torque of actuating shaft.

- Transmission efficiency is lower than in comparison with hydraulic clutch

3.6 Friction clutch

3.6.1 Features of Friction clutch

- Structure is simple, weight and dimensions are small

- Energy loss is small, transmission efficiency is high

- Transition stage is short (unstable working period)

3.6.2 Classification

According to form of friction surface, the friction clutch used on the ships can be classified as follows:

- Disk friction clutch

- Cone friction clutch

- Air-actuated friction clutch

3.6.2.1 Single-disk friction clutch

a Principle

Figure 3.6: Single disk friction clutch

1- Actuating shaft 4- Receiving friction disk

2- Receiving shaft 5- Brake lining (friction material) 3- Actuating friction disk

In a disk friction clutch, the torque is transmitted by friction between surfaces of a disk couple maintained in contact by an axial thrust force

The single-disk friction clutch consists of two-friction disks (3)- actuating disk and (4)- receiving disk, installed on the shafts (1) and (2) The actuating shaft (1) is connected to the crankshaft of the main engine The receiving shaft (2) is connected to the propeller shaft

When the main engine is working, the actuating shaft and the friction disk (3) are turned Due to axial thrust force Q, the friction disk (4) is pressed into the friction disk (3) On the surfaces of the friction disk couple, a friction force is generated: T = µQ (µ- friction coefficient) Therefore, torque of the main engine is transmitted from the actuating shaft (1) to the receiving shaft (2) and it turns the propeller shaft Transmission torque carried out by the friction clutch is equal to friction moment:

M T = M ms = µQ.R tb

Rtb - Average radius of the friction disk couple:

2

min max R R

R tb = +When the axial thrust force Q is stopped, the friction disk couple is released, and revolution of the receiving shaft will decrease and stop

The working process of the friction clutch can be classified by three periods:

- Loading period: This is unstable working state The friction force on the friction disk surface increases from 0 to maximum and revolution of the receiving shaft also gradually increases In this period, revolution of the receiving shaft is always smaller in comparison with the actuating shaft because of relative slip of the friction disks

- Stable working period: Revolution of the actuating shaft and the receiving shaft is the same; transmission torque is equal to friction moment of the friction clutch When operating, a little power is lost so torque on the receiving shaft is little smaller in comparison with the actuating shaft The friction clutch must

be cooled to decrease temperature of the friction disk surfaces

- Unloading period: This is also unstable working state of the friction clutch Revolution of the receiving shaft is little by little decreased and then stopped

In fact, to reduce dimension and increase torque transmission ability, a multiple-disk friction clutch is used (Figure 3.7)

b Material for the friction clutch

Material for manufacturing the friction clutch has to meet the following requirements:

- Abrasion resistance ability is high

- Friction coefficient is high and not depends on temperature

- Friction surfaces must not be stuck to each other at high temperature

- Longevity must be high

- It will not be deformed due to heat

- Heat conductibility is high

Main materials: Cast iron and steel (most commons), brass, asbestos, leather, and wood

3.6.2.2 Cone friction clutch

a Principle

(Figure 3.8)