12.  State about general requirements of marine propulsion plant? How satisfy these requirement?

To operate the ship safely and economically, a marine propulsion plant has to satisfy the general requirements as follow:

+ The transformation of energy is optimum

+ Equipment are simple

+ It is safe and trustful

+ Dimension and weight are small

+ Longevity is high

+ Cost must be low

14.  State requirements about the weight of propulsion plant.

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 it also varied when type of propulsion plant is different.

15.  State requirements about the dimension of marine propulsion plant?

Requirement about dimension of the engine room.

Almost machinery is installed in the engine room. So, the dimension of the engine room has to suit to all of the machinery and the equipment installed in to it. Besides, it must be convenient for maintaining, repairing and safe for operating the machinery of the propulsion the engine room is too large, cargo holds space it reduces the cargo transportation ability of the ship. Therefore, the dimension of the engine room should be calculated to satisfy the both requirements. To perform the requirement about dimension of the engine room, the definitions “saturated coefficient” are used:

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

Volume saturated coefficient of the engine room: the number of horsepower of the propulsion plant in unit of the engine room space.

16.  State requirements about the needments of marine propulsion plant?

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.

17.  State requirements of marine 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.

20.  State the installation principle of shaft line and bearing on board ship?

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 parallels with the keel of the ship; in some case the shaft line is placed unparallel with the keel. It makes with basic line an angle ,  5 (– angle is formed by the shaft line and the keel of the ship in vertical section).

In a propulsion plant with two shaft lines, they are normally installed symmetrically and parallels to the vertical keel section of the ship. In some cases, they make with the vertical keel section angles b (b- angle is formed by the shaft line and the ship vertical keel section), b £ 3o. If a > 5o, b > 3o then thrust force of propeller will be decreased. However, in some special cases a 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.

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 < 22D

Where: D - Diameter of a shaft

                   L - Distance between shaft bearings.

If D < 100 mm, L is calculated: