31.         List the name of all main components and explain sealing principle of the simplex seal type – forward side?

1-              Clamp ring

2-              Forward chrome steel liner

3-              “O” ring

4-              Cover ring

5-              Sealing ting

6-              Intermediate ring

7-              Flange ting

8-              Packing

9-              Stern tube

10-        Aft bulkhead

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

32.         Which substance are used to cool and lubricate stern bearing? Present the requirements for cooling and lubricating by water?

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.

Requirements 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.

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 ³ 20oC.

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

33.         Which substance are used to cool and lubricate stern bearing? Present the requirements for cooling and lubricating by lubricating oil?

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.

Requirements 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.

34. List all main component’s name, explain function and structure specification of intermediate shaft and bearing?

Oiler ring

Access cover for inspection and oiling

Spherical seat

Oil ring guide

Oil deflector ring

Antifriction metal

Minimum oil lever

Spherical seat

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.

35.         What is the function of the thrust shaft and thrust bearing? List the name of all main components of the thrust shaft and bearing?

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 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.

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.

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 nowadays.

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.

36.         How many king of the thrust bearings used on board ship? Explain briefly about all of them?

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 nowadays.

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.

37.         What happen with the main engine parts if thrust bearing to be worn out?

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.

38.         State function of driving equipments and classify driving modes?

Driving equipment and its function

Driving equipment is used to transmit power from the main engine to the propeller.

Driving equipment consist 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.

Classification

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

- Direct driving mode.

- Indirect driving mode.

- Special driving mode.

39.         State features of direct driving mode and indirect driving mode?

Features of indirect driving mode

- 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 the main engine revolution.

- It is commonly applied on the large and medium-sized ships when revolution of the 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.

Features of indirect driving mode

- There is intermediate equipment between the main engine and the propeller to transmit power. In the indirect driving mode, 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:

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 for ahead, one for astern).

- In the indirect driving mode, the main engine is usually a high or medium-speed, four-stroke cycle, non-reversible diesel engine.

40.  State advantages and disadvantages of direct driving mode?

Advantages

- Driving efficiency is high. It does not have any loss other than friction loss in the bearings. 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.

- The propeller efficiency is high (because revolution of the main engine is the same as the optimum range of the propeller revolution).

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

Disadvantages

- The main engine has large dimensions and weight so dimensions and weight of the propulsion plant are increased, 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 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.