Diesel engines are self-ignition engines i.e. fuel is injected into hot compressed air and is ignited. To obtain this, the air inside the engine should be hot which is achieved by pre-heating the engine. Pre-heating heats all parts of the engine which in turn heats the air in the cylinder.
Pre-heating the engine also reduces cold corrosion and there are lesser thermal stresses during starting.
Also, when engine is warm, the clearances are correct, thus lubrication is made easier and there is less chance of undue wear of moving parts.
Pre-heating is usually done using steam or electrical heaters. Hot water is kept in circulation to engine thus keeping all parts in warm condition.
Protection / Precautions against Crank Case Explosion.
Crankcase doors of sufficient strength are provided so that they do not get displaced by crankcase explosion. They must be fastened sufficiently.
One or more crankcase explosion relief doors are fitted, depending on engine size. Crankcase explosion relief valves are fitted with flame arrestors.
Crankcase oil mist detectors (OMD) and monitoring equipment are provided. They give an alarm and also indicate the unit where the mist level is high. Low level of mist is generally an alarm only. But high level of mist gives an alarm / initiates slowdown of the main engine. The OMD must be checked to see it is functional.
High bearing temperature alarms are provided.
Warning notices are provided on crankcase doors indicating doors not to be opened immediately if overheating is suspected.
Crankcase Relief Door & Valve
The figure alongside shows a Crankcase explosion relief door & valve. It consists of:-
A woven wire gauze assembly that does not allow flame to travel out of the crankcase.
A relief valve usually made of aluminum.
A spring against a retaining plate and A discharge hood so designed that products of explosion are discharged in such a way that it does not cause harm to the engine room personnel.
Q) Write short notes on: Use of indicator card on board.
Ans:- Use of indicator card on board:
Power Card is the measurement of the variation of pressures in a cycle.
Irregularities in the shape of the diagram will show operational faults. Maximum or peak pressure may be measured to scale between the atmospheric line and the highest point on the diagram.
Compression diagram is taken in a similar manner to the power card but with the fuel shut off from the cylinder.
The height of this curve shows maximum compression pressure. If compression and expansion lines coincide, it shows that the indicator is correctly synchronized with the engine.
Reduction in height of this diagram show slow compression, which may be due to worn cylinder liner, faulty piston rings, insufficient scavenge air or leaky exhaust valve, any of the which will cause poor combustion.
Draw card or out of phase diagram is taken in a similar manner to the power card, with fuel pump engaged but with the indicator drum 90″C out of phase piston stroke. This illustrates more clearly the pressure changes during fuel combustion. Fuel timing or injector faults may be detected from its shape.
Light or Weak spring diagram is again similar to the power card and in phase with the engine, but taken with a light compression spring fitted to the indicator showing pressure changes during exhaust and scavenge to an enlarged scale.
It can be used to detect faults and scavenge to an enlarged scale. It can be used to detect operations.
Purpose of Deck Mooring Winch and Windlass Winch used on board ship:
Deck Mooring Winch:-
Deck Mooring Winch
Mooring winch is a mechanical device used for securing a ship to the berth. An equipment with various barrels used for pulling ropes or cables, mooring winches play an important role in berthing the ship ashore.
The barrels, also known as winch drums, are used for hauling in or letting out the wires or ropes, which will help in fastening the ship to the berth.
Mooring winches assembly comes in various arrangements with different number of barrels, depending on the requirement of the ship.
The main parts of mooring winch includes a winch barrel or a drum, a warp end and a driving motor. Modern mooring winches comprises of elaborate designs with various gear assemblies, which can be electric, pneumatic or hydraulic driven.
Windlass Winch:-
Windlass Winch
A windlass is a machine used
on ships that is used to let-out and heave-up equipment such as a ship’s anchor
or a fishing trawl. On some ships, it may be located in a specific room called
the windlass room.
An anchor windlass is a
machine that restrains and manipulates the anchor chain on a boat, allowing the
anchor to be raised and lowered by means of chain cable. A notched wheel
engages the links of the chain or the rope.
A trawl windlass is a
similar machine that restrains or manipulates the trawl on a commercial fishing
vessel. The trawl is a sort of big fishing net that is wound on the windlass.
The fishermen either let-out the trawl or heave-up the trawl during fishing
operations. A brake is provided for additional control. The windlass is usually
powered by an electric or hydraulic motor operating via a gear train.
Technically speaking, the
term “windlass” refers only to horizontal winches. Vertical designs
are correctly called capstans. Horizontal windlasses make use of an integral
gearbox and motor assembly, all typically located above-deck, with a horizontal
shaft through the unit and wheels for chain and/or rope on either side.
Vertical capstans use a vertical shaft, with the motor and gearbox situated
below the winch unit (usually below decks).
Q) List the routine
maintenances carried out on board.
Ans:- Efficient planning and
adequate usage of equipments is the key to productive maintenance.
Types of Maintenance Procedures:-
Preventive or Scheduled Maintenance System: – It is famously known as
the PMS or Planned Maintenance System. In this type of system the maintenance
is carried out as per the running hours like 4000 hrs, 8000 hrs etc., or by the
calendar intervals like 6 monthly, yearly etc. of the machinery. The
maintenance is carried out irrespective of the condition of the machinery. The
parts have to be replaced if it is written in the schedule, even if they can be
still used.
Corrective or Breakdown Maintenance: – In this system the maintenance is carried
out when the machinery breaks down. This is the reason it is known as the
breakdown maintenance. This is not a suitable and good method as situations may
occur wherein the machinery is required in emergency. The only advantage of
this system is that the working of machinery parts is used to its full life or
until it breaks. This system might get costly as during breakdown several other
parts may also get damaged.
Condition Maintenance system: – In this system the machinery parts are checked
regularly. With the help of sensors etc. the condition of the machinery is
accessed regularly and the maintenance is done accordingly. This system
requires experience and knowledge as wrong interpretation may damage the
machinery and lead to costly repairs which may not be acceptable by the
company.
Q) With reference to oil monitoring of bilge and tanker ballast discharges: Describe with aid of a sketch, the general arrangements of an oil monitoring system.
Ans:- Oil content monitoring – Working principles & procedure for ship service systems:-
In the past, an inspection glass, fitted in the overboard discharge pipe of the oil/water separator permitted sighting of the flow. The discharge was illuminated by a light bulb fitted on the outside of the glass port opposite the viewer. The separator was shut down if there was any evidence of oil carry over, but problems with observation occurred due to poor light and accumulation of oily deposits on the inside of the glasses.
Present-day monitors are based on the same principle. However, whilst the eye can register anything from an emulsion to globules of oil a light-sensitive photo-cell detector cannot. Makers may therefore use a sampling and mixing pump to draw a representative sample with a general opaqueness more easily registered by the simple photo-cell monitor. Flow through the sampling chamber is made rapid to reduce deposit on glass lenses. They are easily removed for cleaning.
Bilge or ballast water passing through a sample chamber can be monitored by a strong light shining directly through it and on to a photo-cell (Figure 1). Light reaching the cell decreases with increasing oil content of the water. The effect of this light on the photo-cell compared with that of direct light on the reference cell to the left of the bulb, can be registered on a meter calibrated to show oil content.
Another approach is to register light scattered by oil particles dispersed in the water by the sampling pumps (Figure 2), Light reflected or scattered by any oil particles in the flow, illuminates the scattered light window. This light when compared with the source light increases to a maximum and then decreases with increasing oil content of the flow.
Fibre optic tubes are used in the device shown to convey light from the source and from the scattered light window to the photo-cell. The motor-driven rotating disc with its slot, lets each light shine alternately on the photo-cell and also, by means of switches at the periphery, causes the signals to be passed independently to a comparator device, These two methods briefly described, could be used together to improve accuracy, but they will not distinguish between oil and other particles in the flow.
Methods of checking for oil by chemical test would give better results but take too long in a situation where excess amounts require immediate shut down of the oily water separator.
Monitor for oily water using direct light (Figure-1)
Monitor based on scattered light (courtesy Sofrance) (Figure-2)
Tanker ballast:-
Sampling and monitoring equipment fitted in the pump room of a tanker can be made safe by using fibre optics to transmit light to and from the sampling chamber (Figure 3). The light source and photo-cell can be situated in the cargo control room together with the control, recording and alarm console. The sampling pump can be fitted in the pump room to keep the sampling pipe short and so minimize time delay.
For safety the drive motor is fitted in the machinery space, with the shaft passing through a gas-tight seal in the bulkhead. Oil content reading of the discharge is fed into the control computer together with discharge rate and ship’s speed to give a permanent record.
Seris Monitoring System for Tanker Ballast (Figure-3)
Q) With reference to oil monitoring of bilge and tanker ballast discharges: State the Inputs that are recorded and output operation.
Ans:- List of items to be recorded:- (Marpol Annex I)
(A) Ballasting or cleaning of oil fuel tanks
Identity of tank(s) ballasted.
Whether cleaned since they last contained oil and, if not, type of oil previously carried.
Cleaning process:
position of ship and time at the start and completion of cleaning;
identify tank(s) in which one or another method has been employed (rinsing through, steaming, cleaning with chemicals; type and quantity of chemicals used, in cubic metres);
identity of tank(s) into which cleaning water was transferred.
Ballasting:
position of ship and time at start and end of ballasting;
quantity of ballast if tanks are not cleaned, in cubic metres.
(B) Discharge of dirty ballast or cleaning water from oil fuel tanks referred to under section (A)
Identity of tank(s).
Position of ship at start of discharge.
Position of ship on completion of discharge.
Ship’s speed(s) during discharge.
Method of discharge:
through 15 ppm equipment;
to reception facilities.
Quantity discharged, in cubic metres.
(C) Collection and disposal of oil residues (sludge and other residues)
Collection of oil residues: Quantities of oil residues (sludge and other oil residues) retained on board. The quantity should be recorded weekly:* (This means that the quantity must be recorded once a week even if the voyage lasts more than one week)
