EK General exam help for Ocean Navigators from Martin's Marine Engineering Page

Certification Assistance for Canadian Navigators

Canadian Ocean Navigator 
EK Questions and Notes

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Disclaimer
Transport Canada has ask us to advise users of this webpage to keep in mind that these questions are not the exact questions found in their exams. Martin's Marine Engineering Page - www.dieselduck.net is not affiliated with Transport Canada and these questions have been gathered from various sources.

Thank you Walt P. for submitting this material.

 

1 Sketch or describe how a propeller boss is secured to the tail shaft:

The propeller shaft, as its name implies, carries the propeller on its outboard end.
This shaft is also referred to as the tail shaft. It is coupled to the last intermediate shaft and passes out through the stern tube, which carries the weight of both propeller and tail shaft.
The tail shafts outboard end is tapered, and a key with rounded ends sunk into it; the propeller boss fits on this tapered part and the propeller nut screwed on the end to lock the propeller.
A locking finger key is fitted on to the nut, protruding into a hole in the face of the propeller boss to prevent the nut slackening off.

2 Describe with simple sketch the sequence of events in each stroke of an un-supercharged four stroke diesel engine, starting with the induction stroke. Give approximate angels at which the exhaust, induction and fuel valves open.

Induction valve opens at about 15 degrees before TDC of the exhaust stroke and closes at about 35 degrees past BDC on compression stroke, 
Fuel is injected at about 10 degrees before TDC on compression stroke and may continue till about 35 degrees past TDC.
Expansion stroke usually starts a TDC and continues until the exhaust valve opens at about 40 degrees before BDC.
Exhaust stroke carried on until about 15 degrees past TDC on the induction stroke.
These overlaps occur so as to enhance both expansion and also assist in scavenging of cylinders.

3 Using a block diagram, explain the bride control system of a controllable pitch propeller.

4 Using a block diagram explain a bridge control system for a direct reversing diesel.

5 Make a schematic drawing of a data logger. Briefly describe the function of each component.

Sensor transducers are detecting conditions and changes in the plant under control;
pressure, temperature, flow. level, speed, power, position and converting the signals into proportional DC electric outputs. The term transducer means to convert from one form of signal to another.
Scanner receives the DC signal outputs from the sensor-transducers, which are analogues of the physical functions being measured, into channels. The scanner may handle up to 1000 or more different channels, these are dealt with on a rotational basis, and may also be equipped with random access facilities.
Analogue-Digital Converter, would incorporate an amplifier as the voltage signal would need to be amplified and converted into frequency signal, so that it may be suitable for digital measurement and display
An online computer would have a program stored within its memory, and the received signal compared with the program, if these disagree, then the computer will instigate corrective measurements.
In the event of an alarm, a warning bell or horn will sound and a flashing light, corresponding to the alarm condition would be turned on. The audible portion of the alarm can be turned off, however until the problem is remedied the light continues to flash.

6 How is wear down of the stern tube external bearing taken in dry dock.
What is the maximum clearance allowed per centimeter of shaft diameter.
What problems might you encounter if the clearance was too large.

Wear down of stern tube bearings measured regularly, a maximum of 8mm being the usual allowance before the wood stripe ( lignum vitae ) is replaced. the wear down can be measured by either inserting a small wedge between the shaft liner and the outer end of the bearing at the top, or by a poker gauge, with original markings, inserted down through a hole near the end of the stern tube until it touches the shaft.
If wear down becomes too excessive, the consequent bending of the propeller shaft would cause alternating tensile and compression stress as the shaft rotates, this could cause fracture due to fatigue.

7 Describe the warming through process in a steam turbine from cold to ? Ready by Engines?. The main stop on the boiler is shut but steam is raised to about 70% full pressure.

First open all the turbine casing and main steam line drain valves and ensure that all the steam control valves at the maneuvering station and around the turbine is closed. Steam bleed line valves should be opened. Start lubricating pumps and see that the oil is flowing freely to each bearing and gear sprayers are working properly.
Open main injection and discharge valves and start main condenser circulating pump on slow running.
Run condenser extraction pump to maintain a low vacuum of about 200mm Hg.
Change over auxiliary exhaust from auxiliary condenser to main condenser.
Get clearance from the bridge. Turn the engines a little then take out the turning gear.
Ease main steam valve off its face to allow steam into main steam pipe. After all water in the line is driven out through the drains. open the valve very slowly, when the drains are blowing freely, close the drains gradually.
Check that there are no obstruction to sliding feet and take expansion readings, Put on gland steam and crack open maneuvering valves, easing sufficiently to allow a little flow of steam through the engines.
After about 2.5 hours raise vacuum to about 350mm Hg and operate maneuvering valves carefully to slowly turn the engines a few revolutions ahead and astern, repeating this operation about every 10 to 15 minutes for the next 1.5 hours.
At ready for Stand By, after at least 4 hours of heating up, pumps are brought up to normal running speed, vacuum lifted up. and expansion readings checked.
During maneuvering, the turbine drains are regulated as required, and shut off at full away.

8 What is the purpose of supercharging a marine diesel engine.
Use a sketch to illustrate how it is done, and state advantages of turbo charging.

Turbo charging supplies air to the scavenging of the cylinders of the product of combustion, and recharging them with clean air .
The air supply in a supercharged engine varies, often around 200 millibars atmospheric pressure.
The mass of fuel that can be burnt in a cylinder depends on the mass of air present in the cylinder ( about 14 parts of air to 1 part of fuel, with some variations ) at the end of compression. By increasing the amount of scavenge air in a two stroke engine, and by supplying air under slight pressure in a four stroke engine during induction stroke, a greater mass of air can be supplied to the engine. More fuel can then be burned without causing excessive temperature during combustion. 
Burning more fuel produces more heat energy to be implied to the piston, increasing the power of the engine.

9 How is a diesel engine warmed through prior to sailing in the winter months.

A system of warming up diesel engine cylinders is often employed in cooler climates before starting the engine. This will assist the ignition of fuel, reduce wear, minimize corrosion, thermal shock and damage due to sudden unequal expansions.
Water in the cooling system is preheated of about 70 degrees C and circulated around the engine by a separate pump.
Engines burning heavy fuel also requires their fuel valves and pipes lines warmed before starting. These are on a separate circuit, heated by water ( steam ) or mineral oil may be used to ensure good starts.

10 Describe a diesel engine cooling system and name different components in the circuit.

Diesel engines are cooled by circulating a treated cooling liquid ( water ), through its passage in a closed circuit. This coolant is used repeatedly, being piped out of the engine, cooled in a heat exchanger by outside sea water, being circulated by an engine driven pump for this purpose, them discharge overboard. 
It is re-circulated for ice conditions. ( the sea water ).
Temperature is controlled by an automatic temperature regulator.
Coolant may be treated with compounds ( alkaline chromate or organic ) to prevent scale deposits and eliminate corrosive characteristics of the water.
Often an auxiliary pump is fitted as a standby pump and used as an after cooling water pump, circulating coolant for a while after the engine is shut down to remove residual heat from the engine.
An expansion storage tank is located high inside the engine room casing and fitted with a sight glass. The tank will allow for expansion of coolant and accept additives.
Connections are made to the pump suction line and the tank is also fitted with a vent and a fresh water filler valve.

11 What is the purpose of a Governor in a diesel engine.

Two type of GOVERNORS, both employ centrifugal force of flyweights. These are the mechanical or hydraulic governors.
The mechanical governor utilizes the movement of the flyweights to control fuel flow through suitable linkage, while the hydraulic governor, flyweights operate a piston type pilot valve which controls the flow of high pressure oil in a power cylinder. The piston in this cylinder is connected to and, operates the fuel control mechanism.

12 How does lubricating oil become contaminated in a diesel engine?
What are the contaminants and what method are used for purification.

Lubricating oil becomes contaminated through general usage, with water, carbon deposits, and other impurities.
Some of the lube oil in circulation is run through a centrifugal separator and then returned to the sump. Bye pass or full flow filters are used to assists in partial purification.
Samples of the lube oil is taken periodically and sent for analysis to determine viscosity, specific gravity, types of metals suspended in the oil, will determine engine wear, ( bearings )

13 How are light fuel oils and heavy fuel oils prepared before they are injected into the diesel engines. Why is this essential?

Fuel oil is passed through filters capable of removing fine particles of dirt which, if allowed to enter the engine's fuel system, would cause wear of injection-pump plungers and engine cylinders.
Heavy residual fuels may require to be heated and centrifuged to reduce the viscosity of the oil for pumping, centrifuging and injection into the cylinders.
Centrifugal purifiers may be the disc or tubular bowl type. Most are manually cleaned, but some self-cleaning types are on the market.

14 What function does thrust blocks, plumber blocks, and trailing blocks serve?.

Thrust Block- is to transfer the trust of the propeller to the ships structure, transmits the thrust to the hull of the ship.
Plummer Block- a metal bearing for supporting a revolving shaft, with a removable cover to give access to the bearing. This bearing supports the intermediate shaft, and the bottom half only has a white metal lining, and may have a plain surface with oil grooves or a set of bearing pads.
All the bearings are water cooled.
The after most plumber block is white metal lined on both halves ( top and bottom ), it has a trailing collar just clear of the forward face of the block. The purpose of this is to prevent the propeller shaft from sliding aft in the event of fracture of an intermediate shaft. Another function of the trailing collar is to allow disconnection of the shaft coupling forward of this to enable free running of the propeller shaft in case the ship is being towed, Hence this last block is called the TRAILING BLOCK.

15 Describe to operation of a two stroke cycle marine diesel engine, including the cylinder scavenging process.

Piston moving up, exhaust and scavenge ports are closed, fuel valve shut,. Air previously taken into cylinder is being compressed to about 35 bar and 540 degrees C at the end of compression stroke.
At slightly before TDC of compression stroke the fuel valve starts injecting fuel into the cylinder, at TDC ignition of fuel occurs, forcing piston downward, fuel still being injected until about 30 degrees past TDC.
When expansion has reach maximum, about 50 degrees before BDC of cycle exhaust ports open, at about 35 degrees before BDC, the scavenge ports open forcing fresh air into the cylinder, the slope of the air passage is pointing upward thereby assisting in forcing out the exhaust. At about 35 degrees past BDC the scavenge and exhaust ports are closed by the piston, which on the upward movement compresses the air in the cylinder, and the cycle starts all over again.


16 Sketch a bridge speed control unit for a diesel engine vessel. What would be the sequence of events when the control lever is moved to 100 rpm ahead?.

The overriding controller in the engine room must be switched to bridge control.
Speed control lever is moved to 100rpm ahead, the following events would occur;
providing turning gear is out, fuel off, lubricating oil on, cooling water on and starting air lever in the ahead position, starting air would be supplied to the engine
When engine reaches firing speed the starting air is turned off.
If engine is turning in the correct direction, at correct speed the fuel will be supplied.
The fuel supply will be gradually increased to bring the engine up to the desired value.
If engine fails to start, alarm indication would be given, and the sequence would be repeated.

17 What are the advantages and disadvantages of pneumatic, electrical and hydraulic control systems.

Advantages;
Pneumatic systems.
Less expensive than electrical or hydraulic systems.
Leakage are not dangerous.
No heat generated, hence no ventilation required.
Reliability.
Not very susceptible to variations in ships power supply.
Simple and safe.

Electronic system advantages.
Fewer moving parts, less lubrication and wear.
Low power consumption
System is either on or off.
Small and adaptable.
Very quick response

Hydraulic system advantages.
Nearly instant as fluid is virtually incompressible.
Can readily provide any type of motion such as reciprocating or rotary.
Accurate position control.
High amplification.

Disadvantages:
Pneumatic systems
If water ( condensation ect ) enters the system can malfunction.
Loss of air causes loss of control. ( leaks, broken lines ect. )
Dirt in system

Electronic system
Loss of power ( electrical ) renders system useless. Steering being most dangerous, as loss of power usually occurs at the most inconvenient time. ( experienced this in the Fraser River )
Power spikes can blow system.
Poor connections in terminals

Hydraulic systems
Leakage and dirt in system renders them sluggish, or even inoperative.
Loss of power, system becomes inoperative.
Exposure to extreme cold, can freeze moisture in system, and block lines or control lever valves.

18 Describe a lubricating system used in a steam turbine.

The lubricating system serves two functions in a steam turbine.
It provides an film of oil to reduce friction between moving parts;
It removes heat generated in the bearings or conducted along the shaft.

A common lubrication system is used to supply oil to the turbine, gearbox, and thrust bearing, and the gear sprayers. The turbine rotating at high speed, requires a considerable time to stop. If the main motor driven lubricating pump were to fail an emergency supply of lubricating oil would be necessary. This is usually provided from a gravity tank, although main engine driven lubricating oil pumps may also be required.
Oil is drawn from the drain tank through the strainers and the pump to the coolers. Leaving the coolers, the oil passes through another set of filters before being distributed to the gear box, the turbine bearings and the gear box sprayers. Some of the oil passes through an orifice and into the gravity tank from which it continuously overflows. The engine driven pump supplies a portion of the system requirements in normal operation.
In the event of a power failure the gearbox sprayers are supplied from the engine driven pump. The gravity tank provides a low pressure supply to the bearings over a considerable period to enable the turbine to be brought safely to rest.

19 Is it possible to have a crankcase explosion after a diesel engine has been stopped.

YES. When a diesel engine has been stopped the crankcase doors must not be opened until the temperature has dropped to below 120 degrees F, so as to prevent a sudden ingress of air to avoid a possible explosion. The cylinder cooling water pump is left running to bring down the temperature.

20 Explain the cause of scavenge trunk fire and the procedures adopted to extinguish one.

Accumulation of dirt and oil can occur in the scavenge space of a diesel engine. this is caused by such faults as excessive lubrication, slack, worn or broken piston rings, uneven cylinder 
liner wear, damaged air inlet filters, and cracked oil cooled pistons.
If a flame from combustion in a cylinder blows past the piston into the scavenge trunking, this accumulation of oil and dirt could ignite and burn, thus resulting in a scavenge fire.
Indication of a scavenge fires, excessive black smoke, blistering or peeling of paint on scavenge trunking. This is normally local, confined to the vicinity of one cylinder.
Fuel should be shut of to the effected cylinder unit, this reduces temperature. Lubrication increased to prevent seizure and the engine slowed down to reduce air supply to the fire. Most of these fire burn themselves out. In more serious cases, it may be necessary to stop the engine and fight the fire. Some diesel engines have fire detection and CO2 gas smothering systems for scavenge space fires.

21 Describe an automatic float operated tank gauge, how is the signal transmitted to the control room?.

Wesson Tank Gauge- provides continuous readout on a dial gauge or digital counter. They can be arranged to operate on batteries in case of power failure and the transmission system is intrinsically safe.
The gauge consists of a stainless steel tape with a float attached at one end, which is held at a constant tension by means of a tensor spring. The float runs on stainless steel guide wires and as it moves, the tape winds or unwinds on its drum in the gauge housing. Rotation of the drum spindle is used to drive an AC transmitter motor which is connected to an AC synchronous repeater in the control room, and whose dial would be marked of in depth units.

22 Describe a single temperature brine system. Other than a temperature gauge, how can you tell if a chamber is cold and the system working

The simplest form of brine cooling- there is only one evaporator in the refrigerator to produce brine at one temperature only, The same brine is pumped through the cooling pipes of various cold rooms which require to be kept at different temperatures. Provided that the brine temperature is below that of the coldest room, then the quantity of brine flowing through the pipes of any one room determines the temperature of that room. Different rooms can be maintained at different temperatures, by controlling the flow of brine through their separate pipe circuits.
This is done by regulating the amount of opening of the brine return valves at the evaporator, the brine pump discharge valves are left fully open to avoid air locks in the circuit and only closed when repairs are necessary.
In addition to room thermometers, the temperature of the returning brine from any one room can be used to determine the room temperature, 

23 Describe and sketch a turbo charge. What are the advantages of this system.

This is a turbine compressor, the turbine uses energy from the engine exhaust gases and drives an air compressor which supplies air to the engine for scavenging and supercharging.
Advantages are: helps expel exhaust gases, and increases amount of air for compression in cylinder, thereby increasing the amount of fuel that can be burned. This increases the power output of the engine.


24 Describe and sketch a Wheat-stone Bridge.

A balanced circuit OHM meter. The older multi-meters used in electronic circuit tracing comes to mind.
Electrical resistance increases with temperature in most conductive components, some even inversely.( thermistors )
When the balance is upset in the Wheat-stone Bridge, this unbalance or upset can be measured, and converted to indicate temperature, pressure, or flow rate, depending upon application.

25 Describe a thermocouple.

Consists of two dissimilar metals, with the junctions of the metals maintained at a different temperature, an electric current flowed in the circuit.
Advantages are : simplicity, compactness, no external power required, quick to respond to changes of temperature, it is a relatively cheap telemetering device.
Its main disadvantage are small changes in potential for large changes in temperature, needs insulation, and signal requires amplification if signal is to be used in control systems.

26 Sketch and describe the movement of fuel oil from the Double Bottoms to the furnace.

Fuel oil is stored in double bottom tanks and pumped from these as required into settling tanks by means of a transfer pump.
The settling tanks are situated in the stoke hold, two tanks each having a capacity for about 12 hours supply are installed so that the oil can stand for about 12 hours to allow any water in the oil to settle to the bottom and be drained off before use. The oil is drawn from the settling tank, through cold filters into the fuel pressure pump which discharges it at a pressure from 5.5 bar upwards, through a steam operated heater where it is heated to about 90 degrees C depending upon the class of oil, through hot filters into the supply line to the sprayers in the furnace.
There is an oil circulating valve on the furnace distribution valve chest of every boiler which allows the oil to be returned to the pump suction so that any cold oil laying in the pipe line is cleared out for hot oil to tale its place before attempting to light a fire.

27 What is a Venturimeter and describe the principle upon which it works.

A flow sensor meter ( flow rate ) It has a restriction that narrows the pipe, causing a higher pressure before the restriction, and a lower pressure at the expansion of the restriction. The pressure tapping would be fed into a differential cell whose output would be arranged to be proportional to he mass flow rate and therefore be used for display and or control or both.
The meter would be fitted directly into a pipe line or in a bypass line if the main line is of a large diameter.

28 Describe a vapor compression refrigeration cycle.

The compressor draws the refrigerant vapour at low pressure from the evaporator, into the compressor where it is compressed to a high pressure and delivered in through the coils of the condenser in a superheated vapour. As it passes through the condenser coils, the vapour is cooled into a liquid at approximately sea water temperature, the heat given up being absorbed by the sea water surrounding the coils and pumped over board. The liquid, still at a high pressure, passes along to the regulator, this is a valve just partly open to limit the flow through it. The pipeline from the compressor to the regulator is under high pressure, but from the regulating valve to the suction side of the compressor is at low pressure due to the regulating valve being just a little ways open.
As liquid passes through the regulator from a region of higher pressure to a region of lower pressure, some of the liquid automatically flashes off into a vapour absorbing the required amount of heat to do so from the remainder of the liquid and causing it to fall to a low temperature, the temperature being relevant to pressure, so that the refrigerant enter the evaporator at a temperature lower than that of the brine. The liquid now passes through the evaporator coils where it receives heat to evaporate it before being taken into the compressor to go through the cycle all over again. The required heat to turn it into vapour is extracted from the brine, which in turn has been lowered the temperature of the brine.

29 With the aid of a diagram, describe a composite boiler.

Exhaust Gas, heat recovery boiler, mainly used in motor ships.
Hot exhaust gases pass through this boiler, recovery of this waste heat may be used to drive auxiliaries ect.

Notes on pumps 

There are many pumps employed on board ships. These can be divided into two main categories; displacement pumps, and centrifugal pumps. Even within these categories there are several types.
Displacement pumps employ a piston, ram, or buckets within a cylinder drawing in liquid by a reciprocating motion, or by a rotary motion of special designed vanes, gears or rotors.
Centrifugal pumps are those wherein an impeller rotating at high speed throws the liquid by centrifugal force from the center, where incidentally lies the intake or suction, radically outwards to the periphery of the impeller where the liquid is discharged through the delivery outlet.
Generally, displacement pumps of the reciprocating type are suitable for delivering small quantities at high pressure, rotary displacement pumps are used for moderate quantities at a moderate pressure,
Centrifugal pumps are more suited for large quantities at a low pressure. Centrifugal pumps can be designed with a number of impellers in series to attain a high final delivery pressure. Their simplicity makes these pumps suitable for direct drive by electrical motors; centrifugal pumps are gradually replacing reciprocating pumps for most duties

Double Acting Piston Pump- Liquid is discharged from both sides (top and bottom of the bucket)

Gear Wheel Pumps- used for lubrication and fuel oil. Turns counter to delivery side.

Centrifugal Pump- this is a rotary pump, working I on the principle of centrifugal force.

Screw Displacement Pump-Capable of handling intermittent fluid supply, suited for tank cleaning.

Variable Delivery Pumps- This type is usually used in hydraulic systems.
Steering gears, stabilizers, etc., The Hele-shaw pump has a piston and a cylinder in the same plane, but their axis of rotation can be adjusted and made electronic so that the pump can deliver fluid at variables and can alternate between suction and discharge depending upon the eccentricity of the axis. (Suction becomes a discharge port and visa versa.
This pump is driven at a constant speed by an electric motor.

Brought to you by www.dieselduck.net comments to webmaster@dieselduck.net
Disclaimer
Transport Canada has ask us to advise users of this webpage to keep in mind that these questions are not the exact questions found in their exams. Martin's Marine Engineering Page - www.dieselduck.net is not affiliated with Transport Canada and these questions have been gathered from various sources.