Oil Mist Detector

  ¨   Maintenance & Checking accuracy of OMD operation:

¥      Light scatter Type (QMI)

• The light scatter device detector heads are set – up by the manufacturer. systems are self calibrating against deviation.

• Maintenance consists of cleaning lenses and changing filters.
•  The CPU has a self diagnostic facility which checks for errors.
•  The device can be tested by using aerosol which mimics an oil mist at alarm level (2%) LEL.

¥      Graviner type

• Alarms & slowdown are tested against a known concentration of mist
• The lenses and mirrors should be cleaned periodically.
• In this model the total mist concentration is measured with respect to clean air.
• An alternative models draws samples through both references and measuring tubes which from C/C and atmosphere and compare the level of mist.

  ¨   Take to safeguard against the risk of C/C explosion in the event of OMD become inoperative:

• If the engine is not equipped with bearing temperature monitors linked to slowdown/shutdown, then in the event of the oil mist detector becoming inoperative, then subject to classification society rules, the machinery space cannot operate under UMS conditions and will have to be manned on a 24 hours watch keeping basis.
• Because one of the important safety devices is now inoperative, extra vigilance will be required by the engineers on duty.
• If bearing temperature probes are fitted, then these must be closely monitored.
• The watch keeping engineer must use his senses of smell, hearing, sight and touch to check for any unusual noise, heat or smell which may indicate a potentially dangerous situation. In the event of any doubt, them the engine must be stopped for further investigation.
• It will be even more important than ever to ensure that the engine is not overloaded.
• The crankcase pressure should be closely monitored; a rise in pressure on a trunk piston engine will indicate excessive blow by from one or more units.

The OMD should be investigated to establish the cause of failure, and necessary spares ordered to rectify the problem as soon as possible. 

Midship section

Container Ship

Purpose of Torsion Box in a container ship:

       Problems may arise in these vessels due to the lack of torsional strength caused by the large hatches.

       This problem is overcome to some extent by fitting torsion boxes on each side of the ship.

       These boxes are formed by the upper deck, top part of the longitudinal bulkhead, sheer strake and upper platform, all of which are of thick material.

       The boxes are supported inside by transverses and wash bulkheads in addition to the longitudinal framing.

       These boxes are only effective if they are efficiently tied at their ends.

       At the after end they extend into the engine room and are tied to deep transverse webs.

       Similarly at the fore end, they are carried as far forward as the form of the ship will allow and are welded to transverse webs.

       The longitudinal bulkheads below the box may have to be stepped inboard to suit the shape of the ship, the main longitudinal bulkhead being scarphed into the stepped section.

                                           

Fuel Injector (drawing)

MORONS AT HEATHROW

Two guys have wasted their time at airports, in this case, London’s Heathrow, by writing down strange names and asking the airport Information Center to locate these people by calling out their names on the airport’s PA system.  These guys would then hang out beneath the speakers and record the results.

In order to make it as believable as possible, they dressed up as chauffeurs and asked for help finding these people about 40 minutes after a Thai Airways or Air India flight had landed.

They acted as if they could not pronounce the names themselves, so as not to reveal the joke, but just handed over a note with the names printed on it and asked the employ at the Information Center.

After the fifth recording, they had to leave Heathrow as airport security figured out what was going on.  The last recording is from Gatwick.

To hear the recordings, double-click on the speaker symbol (it’ll take a few seconds to start), listen and enjoy.

Give these guys the Big Practical Joker prize.

Looks Like…	Reads Like…	Sounds Like…
Arheddis Varkenjaab and Aywellbe Fayed	I hate this fucking job, and I will be fired
Arhevbin Fayed and Bybeiev Rhibodie	I‘ve just been fired, and bye-bye everybody
Aynayda Pizaqvick and Malexa Kriest	I need a piss quick, and my legs are crossed
Awul Dasfilshabeda and Nowaynayda Zheet	Oo-ah, that feels better and now I need a shit
Makollig Jezvahted and Levdaroum DeBahzted	My colleague just farted, and left the room, the bastard
Steelaygot Maowenbach and Tuka Piziniztee	Still, I got my own back and took a piss in his tea

Impressed Current Cathodic Protection (ICCP)

The principle of impressed current systems is that

§  Voltage difference is maintained between HULL ßà ANODES, which protect the hull against corrosion.

§  Anodes are made of non-consumable lead/silver, platinum/palladium alloys or platinized titanium.

§  The amount of current is monitored and controlled by the controller. Otherwise, there will be overprotection with wastage of current.

§  Reference cells (made of silver/silver chloride) detects the voltage between

HULL ßà REFERENCE CELL

§  An amplifier controller is used to amplify the micro-range reference cell current and it compares this with the preset protective potential value, which is to be maintained.

§  Using the amplified D.C. signal from the controller the reactor rectifier supplies larger current from ship’s A.C. power source.

§  Although the first cost is considerable, the savings on hull maintenance over the life of the ship is considerable.

Electrical Installation on Ship's

AC Generators - how they work

Vast majority of ships use alternating current (ac) generators (often called alternators). The basic principle of an ac generator is very simple. Pairs of magnetic poles are driven (by the prime mover) past fixed coils of wire.

 An alternating electromotive force (emf) which has a sinusoidal waveform, is induced into each coil:

622 V

440V   440 V

 

EMF (voltage)  generated depends on the strength of magnetic flux ((D) and the rate at which this flux cuts the coils –

EMF µ Strength of magnetic field x Speed of rotation EMF µ Strength of magnetic field x Speed of rotation

The FREQUENCY (measured in Hertz) of the emf generated is the number of waveform cycles per second. Above figure shows 1 cycle.

These two basic relationships for emf size and frequency dictate how to control the voltage and frequency output of a generator.

In practice the speed is maintained practically constant by the generator's prime mover (governor) which fixes the output frequency  normally 60 Hz. The constant speed then allows the size of generated emf   (440V RMS) to be controlled by the adjusting the strength of magnetic field (excitation).

 

Generator Rating

The generators form the heart of the electrical design and their correct sizing is the key to a safe, workable and economical system. Main generator electrical power ratings range from, typically, 100kW to 2MW at 440V, 60Hz. Capacity of generators depends up on the nature of the load. In addition to satisfying load requirements under different conditions e.g.

• Cargo operation
• Anchorage
• Drydock
• Navigation at sea
• Manoeuvring

The generator often works on its own and is subjected to large system load swings during starting of equipment like air compressors, winches, ballast pumps, cargo machinery, and air-conditioning.

International maritime regulations (e.g. SOLAS Chapter II-1,), require at least two generators for a ship's main electrical power system. The generators are normally driven from their own dedicated diesel engine but this can be expensive, taking up additional space that could be used for other purposes. For ships engaged on long sea voyages, it can be economical to drive the generators from the main propulsion plant  (shaft generator) or from waste heat (Turbo alternator).

International maritime regulations also require at least one electrical generator to be independent of the speed and rotation of the main propellers and associated shafting and accordingly at least one generator must have its own prime mover.
If a minimum of two generators is provided, one of which is driven from the propeller shaft, failure of one of the generators could make the ship non-compliant with the International regulations.

For this reason many owners opt to provide three generators. One is used for the normal sea load (e.g. the shaft generator), leaving two available to meet any unusually high loads or to provide security when manoeuvring. Alternately, the third is retained as a standby set able to provide power should one set fail in service or require specific maintenance work. 

Main Switchboard
The main elements of a marine distribution system are the main and emergency switchboards, power panel boards, motor controllers, lighting and small power panel boards. The system is generally designed such that under all normal conditions of operation, power is distributed from the main switchboard.

The main switchboard is generally located  in the main engine room or machinery control room. These locations are normally below the ship's waterline or below the uppermost continuous deck of the ship i.e. the bulkhead or main deck. Consequently, in the event of a fire or flooding it is likely that the main generators and switchboard would be disabled.

To ensure that electrical supplies are available to emergency and safety systems, an emergency generator and associated emergency switchboard will be located above the main deck in a separate space, completely isolated from the main machinery spaces.

Motor Controls

It is often convenient to group motor driven auxiliaries according to their function, e.g. fuel and lubrication oil services, accommodation ventilation systems, machinery ventilation systems, and domestic service systems. This can often simplify the machinery control functions and required protection systems.

Protective systems are provided to shut down all ventilation systems and all fuel oil systems in the event of fire from a remote location.

Describe the use of circuit-breakers and fuses

A circuit breaker safely makes and breaks the power supply to an electrical circuit. In case of short circuit when current flow exceeds the safe limit, circuit breaker trips and interrupts the power supply. Circuit breaker can be reset and used again. The fuse on other hand burns out and needs to be replaced. Before carrying out maintenance, the power supply to the circuit is cut off by switching off and locking the main circuit breaker.

The purpose of a fuse isto protect a circuit from damage when excessive current flows. Fuses are designed to blow rapidly before excessive current can damage the circuit they protect. When a fuse blows it must be replaced by a fuse of same type and same rating.

One can remove the fuse and be sure that equipment is dead, if there is need to work on it.

Emergency Power

WHY  EMERGENCY SOURCE OF ELECTRICAL POWER IS PROVIDED?

Emergency switchboard is smaller than the main switchboard. It is provided so that in the event of an emergency involving a total power failure, a supply will still be available for emergency lighting, alarms, communications, watertight doors and other services necessary to maintain safety and to permit safe evacuation of the ship by lifeboats.

Emergency switchboard is generally arranged to be above the bulkhead deck and readily accessible from open deck.

POWER SUPPLY FOR THE EMERGENCY SWITCH BOARD

• Emergency switchboard is normally supplied power from main switchboard through BUS TIE CIRCUIT BREAKER.

• When the mains power fails, the emergency switchboard is supplied by its own independent power source (emergency generator).The emergency source of power must be self contained and not dependent upon any other engine room power supply. It should be capable of functioning when the ship is inclined by 22.5⁰ and/or trim of 10⁰

Starting arrangement for emergency generator

• Emergency generating sets shall be capable of being readily started in their cold condition at a temperature of 0⁰C.

• Each emergency generating set arranged to be automatically started with compressed air, hydraulic or electric means. The stored energy for starting should be sufficient for 3 consecutive starts.
• Additional energy for 3 consecutive starts with in 30 mins is available.

• The energy storage device (electric battery or compressed air) is always kept charged.

• Some generators may have manual starting by hydraulic accumulator or hand cranking.

Sources of Emergency Power Supply

 

A.        ACCUMULATOR BATTERY capable of carrying load, with not more than

12% volt drop during discharge period. Automatically supplying power to emergency switchboard in case of mains power failure. or

B. GENERATOR, capable of starting automatically from cold within

45 seconds, and using fuel of flash point above 43⁰C

TRANSITIONAL SOURCE (BATTERIES) Power for half an hour is provided along with emergency diesel generator

(a) In Passenger ships - To supply power during momentary blackout before emergency generator comes on load within 45 seconds, so that passengers don’t panic.

(b)In Cargo ships - To supply selected power, if the emergency generator is hand starting type.

INTERLOCKS FOR PROTECTION

Interlocks are provided such that power is supplied from only one source at a time to the emergency switchboard i.e. mains supply or emergency generator, so that the circuit breakers of the two supplies cannot be closed together.

Closing of two circuit breakers in a.c. system, without synchronising the phase, will cause short circuit and damage to the equipment.

List the essential services to be supplied from the emergency generator

 

Emergency switchboard supplies power to the following essential services.

TIME PERIOD - FOR PASSENGER SHIPS - 36 HOURS (SOLAS).

FOR CARGO SHIPS            18        HOURS. (SOLAS)–

(Transitional batteries supply power to service  NO.1 & 2 for half an hour)

SERVICE No 1.EMERGENCY LIGHTS

(a) Embarkation station on deck and overside.

(b) Lighting in alleyways, staircase and exits.

(c) Machinery space,   generators and their control position.

Emergency switchboard, steering compartment, emergency fire pump, storage for fireman's outfit, emergency bilge pump.

(d)       Navigation lights, not under command lights.

 SERVICE NO 2. COMMUNICATION AND ALARMS

(a)        Internal communications as required in an emergency, radio,

            telephones.

(b)        Fire detection and alarm system.

(c)        Intermittant operation of day light signalling lamp, ship's

            whistle, manual fire alarms.

3.NAVIGATIONAL AIDS-Radar,ARPA,Radio direction finder,Gyrocompass, Echo sounder,Radio equipment,Rudder angle indicator,speed log etc.

4. EMERGENCY FIRE PUMP - if electrically driven.

5. STEERING GEAR - for 30 minutes for a vessel above 10,000 tons.

Supplementary emergency lighting for ro-ro  passenger ships

Consists of fixed or portable lighting.

Fixed Lighting

All passenger public spaces and alleyways are provided with supplementary electric lighting that can operate for at least 3 h when all other sources of electrical power have failed and under any condition of heel.

The illunimation provided is such that the approach to the means of escape can be readily seen.

The source of power for the supplementary lighting consists of accumulator batteries located within the lighting units that are continuously charged, where practicable, from the emergency switchboard. These batteries are replaced at regular interval as per maintenance requirements.

Or

Portable lighting

a portable rechargeable battery operated lamp is  provided in every crew space alleyway, recreational space and every working space which is normally occupied unless supplementary emergency lighting.

NOTE - It must be noted that there is no fixed arrangement, because all ship's differ in some respect. This gives the basic concept. Some ships may have a diesel driven emergency fire pump. Others may have only batteries as an emergency power source, which supply limited power to few essential services. This depends upon the type of ship and safety regulations applicable to it.