Marine Engineering Knowledge
Marine engineering is a complex field that demands a deep understanding of both theoretical principles and practical applications. Whether you’re preparing for exams or looking to enhance your professional knowledge, having a comprehensive resource is key to mastering the subject. “Marine Engineering: The Best Marine Engineering Q&A of 24-25” is designed to provide you with the most relevant and up-to-date questions and answers, covering essential topics such as engine maintenance, safety protocols, propulsion systems, and auxiliary machinery.
This guide offers clear, concise explanations and practical insights, helping marine engineers at all levels stay ahead in the ever-evolving maritime industry. From troubleshooting critical systems to understanding advanced operational procedures, this Q&A guide is your go-to resource for success in marine engineering in 2024 and beyond.
Engineering Knowledge Part 1
Q 1: What is ovality of auxiliary engine crank pin?
Ans: Ovality is the deformation of the crank pin from its circular shape to an oval form, caused by reduced lubrication effectiveness and connecting rod thrust. It’s most prominent at 45 degrees ATDC and can lead to damage if it exceeds 1/4th of the bearing clearance. Ovality is corrected by in-situ grinding, with a maximum removal limit of 2mm to maintain surface hardness.
Q 2: Why are concentric springs fitted for auxiliary engine (A/E) cylinder head valves?
Ans; Concentric springs prevent surging by using two springs with different vibration characteristics, minimizing resonance. They also provide safety by ensuring the valve remains in place if one spring fails, offering reliable and efficient valve operation
Q 3; What is a Coalescer?
Ans; A coalescer is a device that promotes the merging of small liquid droplets, such as oil, into larger droplets, making it easier to separate them from gases or other liquids.
Q 4 : What is the function of a L.P. controller?
Ans: The L.P. (Low-Pressure) controller stops the compressor when the suction pressure drops, usually due to the closure of compartmental solenoids. It restarts the compressor when the suction pressure rises as the solenoids reopen.
Q 5; What is the function of an L.P. cutout?
Ans: The L.P. (Low-Pressure) cutout protects the compressor by stopping it if suction pressure drops too low, preventing damage from refrigerant loss or blockages. It also prevents air and moisture from entering the system if pressure falls below atmospheric levels.
Q 6: How to prepare a DB fuel oil tank for a survey/inspection?
Ans: To prepare a DB fuel oil tank, empty and strip oil, clean with seawater, ventilate using cross ventilation, check for explosive gases, and complete necessary certificates and checklists.
Q 7: Why are CO2 bottles provided with dip tubes?
Ans: Dip tubes ensure only liquid CO2 is drawn, preventing nozzle freezing and enabling rapid discharge (85% in 2 minutes) as the liquid expands into gas.
Q 8; What is the significance of firing order?
Ans: The firing order ensures balanced primary and secondary inertia forces, assists in exhaust grouping, distributes stress evenly along the crankshaft, optimizes bearing loading, and provides a consistent turning moment.
Q 9: What is a node?
Ans: A node is a point in a vibrating medium where deflection is zero and amplitude changes sign. More nodes indicate a higher natural frequency.
Q 10: What is a forcing frequency?
Ans: Forcing frequency refers to frequencies caused by cylinder firing impulses on the crankshaft, creating complex waveforms with harmonics like 1x (first order), 2x (second order), and 3x (third order).
Q 11; What is balancing?
Ans: Balancing controls vibrations by ensuring out-of-balance forces and couples are minimized or canceled out to acceptable levels.
Q 12: How are resonance frequency, forcing impulses, and stresses adjusted?
Ans: They are adjusted by modifying shaft sizes, propeller blade count, firing order, using dampers, balancing weights, and detuning couplings.
Q 13: How are axial vibrations caused in the crankshaft, and how are they remedied?
Ans: Axial vibrations in the crankshaft occur when gas pressure on the crank throw causes axial deflection, potentially transferring vibrations to the hull via the thrust bearing. The remedy is to apply axial damping to the crankshaft.
Q 14; Why is starting air overlap provided in a diesel engine?
Ans; Starting air overlap ensures positive engine start in the correct direction, allows starting from any position, and enables the engine to start even if one starting air valve malfunctions.
Q 15: What are the advantages of uniflow scavenging?
Ans: Uniflow scavenging offers simple liner construction, requires no long piston skirt, allows for increased stroke length, improves scavenging and thermal efficiency, burns low-grade fuel, ensures uniform wear, reduces thermal stress, minimizes air-gas mixing, and optimizes exhaust valve timing.
Q 16: What are the causes of turbocharger surging?
Ans: Turbocharger surging can be caused by rapid load changes, choked exhaust or air passages, fuel system issues, blocked air filters, fouling, unbalanced engine output, damaged exhaust valves, or scavenge fires.
Q 17: What is the normal relief valve setting of a cylinder head in a diesel engine?
Ans: The relief valve is typically set 10–14.5% above the working pressure, around 120 bar, slightly higher than the maximum pressure.
Q 18: Why is cylinder liner wear more at the top?
Ans: Cylinder liner wear is higher at the top due to high combustion temperatures, reduced lubrication, acidic corrosion, fuel deposits, and piston direction changes causing step formation at the reversal point.
Q 19: What are the causes of cylinder head cracking?
Ans: Cylinder head cracking can result from scale deposits, poor cooling, uneven bolt tightening, fluctuating coolant temperature, engine overloading, faulty relief valves, gas and acidic corrosion, and water-side corrosion.
Q 20: What are the reasons for a piston crown to crack?
Ans: Piston crown cracking can result from casting defects, thermal stresses, scavenge fires, overheating (cooling failure or deposits), after-burning, and faulty fuel injection.
Q 21: What are the reasons for black smoke from a diesel engine?
Ans: Black smoke can be caused by poor combustion, low compression, insufficient scavenging air, fouled exhaust, broken piston rings, ineffective lube oil seal, after-burning, bad fuel, faulty cylinder lubrication, and low air/fuel efficiency during starting.
Q 22: What are the different types of top bracing for a diesel engine?
Ans: Top bracing types include stiff connections with adjustable friction plates and hydraulic top bracing, which raises natural frequency to prevent resonance at normal engine speeds.
Q 23: What is a thermostatic expansion valve?
Ans; A thermostatic expansion valve (TXV) regulates refrigerant flow from high to low pressure, ensuring efficient heat absorption and preventing liquid refrigerant from entering the compressor. It maintains a superheat of 6 to 7 degrees Celsius, protecting the system and ensuring optimal performance.
Q 24: Why are heaters provided in a refrigeration compressor crankcase?
Ans: Heaters prevent lube oil carryover by aiding refrigerant-oil separation, maintain oil viscosity for effective lubrication, and prevent oil flocculation that could block passages.
Q 25: Why is a relief door not fitted in a refrigeration compressor crankcase?
Ans: A relief door is omitted to prevent air contamination, as no oxygen is present, incoming refrigerant is cold, and the crankcase serves as the compressor’s suction chamber, risking air and moisture intake.
Q 26: What is the SQUAT Phenomenon?
Ans: The SQUAT phenomenon occurs when a vessel moves through shallow water, causing it to sink lower due to a venturi effect. This increases the draft, raises engine load, and reduces steering ability, posing risks in shallow areas.
Q 27. What are the various windlass safeties?
Ans: Electric: Electromagnetic brake, motor overload protection, short circuit protection, restart delay timer, and restart stop.
Manual: Manual/mechanical brake, cable stopper, slipping clutch (torque limiter), and relief valve.
Q 28; What are the functions of lube oil in a refrigeration system?
Ans: Lube oil in a refrigeration system provides lubrication, seals the clearance spaces between discharge and suction sides, acts as a coolant, helps with capacity control, and dampens compressor noise.
Q 29; What are the reasons for foaming in a refrigeration compressor crankcase?
Ans: Foaming occurs due to rapid boiling of refrigerant dissolved in the oil when pressure drops. Causes include liquid in the suction line, faulty crankcase heater, high compressor capacity at startup, incorrect expansion valve superheat, or low oil charge.
Q 30: What is critical temperature?
Ans: Critical temperature is the temperature above which a gas cannot be liquefied, regardless of pressure applied.
Q 31: What is critical pressure?
Ans: Critical pressure is the pressure at which a gas will liquefy at its critical temperature.
Q 32: What are the overhead crane safeties?
Ans: Overhead crane safeties include a solenoid-operated brake for power failure, limit switches for movement limits, overload trip, dead man’s handle, pulley guards, locking device on the lifting hook, and mechanical locking for stability in heavy weather.
Q 33: What is a 1st order moment?
Ans: A 1st order moment acts in vertical and horizontal directions. It is typically minor in engines with 5+ cylinders but can be significant in 4-cylinder engines, potentially causing hull resonance. A 1st order compensator with counter-rotating masses can mitigate these effects.
Q 34: What is a second order moment?
Ans: A second order moment acts vertically and affects 4, 5, and 6-cylinder engines. It may cause resonance in hulls with over 3 nodes. A compensator with counter-rotating masses at twice the engine speed mitigates this.
Q 35: What are the methods to manage second order moments?
Ans: Second order moments can be managed by using compensators mounted at the aft or fore end, driven by the engine’s chain drive, or by installing compensators at both ends to fully eliminate the external moment.
Q 36: What are the air bottle safeties?
Ans: Air bottle safeties include a relief valve, fusible plug, drain, and low-pressure alarm.
Q 37: What are constant tension winches?
Ans: Constant tension winches use variable capacity pumps with automatic control to maintain constant system pressure and motor torque, ensuring steady tension during both drawing in and paying out.
Q 38; What are the steering gear motor safeties?
Ans:Steering gear motor safeties include overload and high-temperature alarms, 200% motor insulation, self-start after power failure, short circuit trip, phase failure alarm, and emergency bus power for one motor. Hydraulic safeties include low-level and high lube oil temperature cutouts.
Q 39: What are the types of vibration in a diesel engine, and which is most damaging?
Ans: Types of vibration include linear, torsional, and resonant. Torsional vibration is the most damaging, particularly to the crankshaft and propeller shafting.
Q 40: If resonance occurs, what is the solution?
Ans: Solutions for resonance include using Lanchester balancers for 2nd order vertical moments, adjusting crankshaft counterweights for 1st order vibrations, adding primary and secondary balancers, and adjusting side stays.
Q 41: What is under critical running?
Ans: Under critical running adjusts the natural frequency to avoid resonance within 35-45% above maximum engine speed. Characteristics include a short shafting system, minimal or no turning wheel, large shaft diameter, and no barred speed range.
Q 42: What is overcritical running?
Ans: Overcritical running adjusts the natural frequency so that resonance occurs 30-70% below engine speed at maximum continuous rating. Characteristics include a high-inertia turning wheel, a smaller-diameter shaft, and a barred speed range around the critical speed.
Q 43: What is an electric compensator?
Ans: An electric compensator, usually placed in the steering gear compartment, neutralizes external forces by synchronizing with them in the correct phase. It requires additional seating for installation.
Q 44: How do you test a fresh water generator plant for leaks?
Ans: Close all outlet valves, inject air to pressurize the shell up to 1.0 bar, and apply soap solution to joints and suspected areas to identify leaks.
Q 45: What are guide force moments and their types?
Ans: Guide force moments, originating from the connecting rod’s angularity, cause transverse forces on the crosshead. They can lead to engine vibrations: H moments induce rocking, and X moments cause twisting. These moments are generally harmless but may require top bracing if resonance occurs.
Q 46: What happens if a fuel pump leaks?
Ans: A fuel pump leak reduces fuel quantity, causing power loss, late injection, after-burning, high exhaust temperatures, smoky exhaust, and power imbalance among units.
Q 47: What actions should be taken if the stern tube of a ship starts leaking?
Ans: Maintain low head, use higher viscosity oil, periodically replenish oil, drain water, and try removing foreign particles by reversing the shaft direction.
Q 48: What are the vibration characteristics of low-speed 2-stroke engines?
Ans: Low-speed 2-stroke engines exhibit external unbalanced moments, guide force moments, and experience both axial and torsional vibrations in the shafting system.
Q 49: How are torsional vibrations generated?
Ans: Torsional vibrations arise from varying cylinder gas pressure and crankshaft torque during the working cycle, along with propeller interactions in a non-uniform wake. Remedies include adjusting crankshaft diameter and using a torsional damper.
Q 50: What are the critical speed effects?
Ans: Critical speed effects include resonance, torsional vibration, and potential fatigue failure. These can be mitigated using detuners, vibration dampers, or an electric vibration compensator unit.
Q 51: What is the volumetric efficiency of an air compressor?
Ans: Volumetric efficiency is the ratio of the actual volume of air drawn in to the swept volume.
Q 52: What is the usual volumetric efficiency of a diesel engine?
Ans: For naturally aspirated engines, it’s 0.85–0.95; for supercharged engines, up to 4.0; and for 2-stroke engines, 0.85–2.5.
Q 53: What is compression ratio?
Ans: Compression ratio is the ratio of (swept volume + clearance volume) to clearance volume.
Q 54: What is brake thermal efficiency?
Ans: Brake thermal efficiency is the ratio of energy developed at the brake to the energy supplied, representing the heat converted to useful work during combustion.
Q 55: What causes reduced output in a centrifugal pump?
Ans: Reduced output is caused by friction and leakage losses, low suction head, choked filters, worn wear rings, air ingress, low motor voltage, impeller cavitation, and improper maintenance.
Q 56: What causes vibration in a vertical centrifugal pump?
Ans: Vibration is caused by shaft misalignment, worn bearings, loose foundation bolts, improper impeller clearances, damaged coupling bolts, worn bottom bush, debris deposits, and corrosion or erosion on rotating parts.
Q 57: What is the function of a solenoid valve in a refrigeration system?
Ans: A solenoid valve controls refrigerant flow based on temperature, shutting off when the compartment reaches the thermostat’s low set point and opening when it exceeds the high set point.
Q 58: What are the advantages and disadvantages of synthetic lube oils?
Ans: Advantages: Improved low-temperature fluidity, better high-temperature retention, reduced friction, less thickening from oxidation, and lower high-temperature deposits.
Disadvantages: Higher cost (6–12 times more) and limited availability.
Uses: Commonly used in air compressors, purifiers, and hydraulic units.
Q 59: What is the function of a back pressure valve in a refrigeration system?
Ans: The back pressure valve, located at the evaporator coil exit in multi-temperature systems, maintains pressure equilibrium, ensuring refrigerant flow prioritization to lower-temperature compartments. It is a spring-loaded non-return valve.
Q 60: What is the function of driers in a refrigeration system?
Ans: Driers absorb moisture in the refrigerant, using activated alumina or silica gel, and are located in the main liquid line with a charging connection.
Q 61: What safety features are included in the refrigeration system?
Ans: Refrigeration system safeties include HP and LP cutouts, lube oil pressure cutout, condenser relief valve, belt drive, cylinder head relief valve, low flow/high temperature alarm, motor overload, oil separator, drier, mechanical seal, unloaders, non-return valves, and temperature and pressure sensors.
Q 62: Why is the refrigerator compressor belt-driven?
Ans: A belt drive reduces risks of shaft seal leakage from misalignment or vibration and limits compressor damage from liquid entry by allowing belt slippage.
Q 63: How can you detect air in the refrigeration system, and what is the procedure for purging it?
Ans:
Detection: Signs of air include high condenser pressure, bubbles in the sight glass, elevated discharge pressure, increased superheat, pressure fluctuations, and reduced efficiency.
Procedure for Purging Air:
- Measure refrigerant pressure and temperature at the condenser outlet.
- Compare the temperature with the saturation temperature on the P-T chart to check for sub-cooling.
- Adjust cooling water flow to achieve near-saturation in the condenser.
- Close the liquid outlet valve, circulate cooling water, start the compressor, and pump down the refrigerant to prevent air ingress by keeping suction pressure above atmospheric.
- Continue circulating cooling water until inlet and outlet temperatures equalize, confirming pump-down.
- Compare condenser pressure with refrigerant saturation pressure from the P-T chart based on sea water outlet temperature.
- If they differ, release air through the vent until the pressures align with saturation conditions.
Q 64; Why is intercooling provided in an air compressor, and why is compression divided into stages?
Ans: Intercooling reduces work by aiming for isothermal compression, lowers outlet temperature to prevent oil oxidation, minimizes deposits, increases air density, removes moisture, and enables even load distribution by staging.
Q 65: What happens if compressor motor connections are reversed after overhauling?
Ans: Reversed connections can lead to insufficient lube oil pressure, causing low-pressure trips and potential damage to moving parts. Additionally, the shaft-driven cooling water pump may fail to generate enough flow, triggering trips due to non-flow or high air temperature.
Q 66: What is the function of an H.P. cut-out in a refrigeration system?
Ans: An H.P. cut-out is a safety device that trips the compressor if the discharge pressure exceeds safe working levels.
Q 67: What are the usual stern tube bearing clearances?
Ans: Water-cooled stern bearing clearance is typically 8–12 mm, while oil-cooled stern tube bearing clearance is around 1.87–2.0 mm.
Q 68: What is the method for measuring propeller drop?
Ans: Propeller drop is measured by using a dial gauge to check the vertical displacement of the propeller shaft from a fixed reference point.
Q 69: What is the usual propeller drop value?
Ans: The usual propeller drop is 1 mm per 160 mm of shaft diameter.
Q 70: What is Lignum Vitae?
Ans: Lignum Vitae is a durable wood used in traditional seawater-lubricated stern tube bearings for its self-lubricating properties in water. It’s fitted axially, with V or U grooves for water flow and debris collection, secured by bronze keys and screws.
Q 71: What is the material of the ship side valve?
Ans: Ship side valve body is typically made of nickel-aluminum bronze or cast steel, with stem, seat, and disc made of Monel metal (Cu= 2:1) for excellent seawater resistance and durability.
Q 72: What material is used for propellers?
Ans: Propellers are made of nickel-aluminum bronze (55–62% copper, 0.5–2.2% aluminum, 0.5% nickel) or manganese bronze (58% copper, 1% iron, 1% aluminum, 1% manganese).
Q 73: What material is used for a 4-stroke engine connecting rod?
Ans: 4-stroke engine connecting rods are typically made from forged carbon steel or 3% nickel steel for high strength and durability.
Q 74: What material is used for boiler tubes?
Ans: Boiler tubes are made from low-carbon alloy steels containing chromium, nickel, and molybdenum.
Q 75: What material is used for boiler gauge glass?
Ans: Boiler gauge glass is made from toughened glass, typically containing silicon oxide, magnesium oxide, borosilicate, or lime soda glass.
Q 76: What is the typical composition of stainless steel?
Ans: Stainless steel typically contains 18% chromium, 8% nickel, and 0.12% carbon.
Q 77: How does an engine flywheel compare to its governor?
Ans: A governor maintains engine speed by adjusting fuel flow, while a flywheel smooths RPM fluctuations through inertia. The governor actively controls RPM changes, whereas the flywheel relies solely on inertia to stabilize rotations.
Q 78: What is the purpose of tie rods?
Ans: Tie rods keep the engine structure in compression, enhancing fatigue strength and maintaining gear alignment. They prevent tensile stress during peak firing, reducing risk of structural damage.
Q 79: What is the material of the double bottom plug?
Ans: Silicon steels
Q 80: Why are tie rods positioned near the crankshaft centerline?
Ans: Tie rods are placed near the crankshaft centerline to limit bending and distortion of the bearing housing caused by firing forces on the transverse girders.
Q 81: What is the crank web length?
Ans: The crank web length is half the stroke length (stroke/2).
Q 82: What is the material of the crankshaft?
Ans: Forged low carbon alloy steel. Carbon: 0.12% and less
Q 83: What are the typical bearing failures?
Ans: Typical bearing failures include fatigue cracks, tin oxide deposits, surface wiping, overlay tearing, acidic corrosion, cavitation, erosion, dross inclusion, spark erosion, and bacterial damage (honey-colored deposits)..
Q 84: What are the advantages of a thin shell bearing?
Ans: Thin shell bearings provide superior fatigue resistance, excellent load-bearing capacity, and good embedability and conformability. They require no bedding, are lightweight, easy to store and install, have enhanced mechanical strength, and offer efficient heat transfer due to uniform contact with the housing.
Q 85: What is the location and purpose of a thrust bearing in an auxiliary engine?
Ans: The thrust bearing, typically near the drive end, controls crankshaft axial movement and absorbs axial loads, ensuring alignment and reducing wear.
Q 86: Why is lube oil analysis important?
Ans: Lube oil analysis detects oil deterioration, contamination levels, and internal machinery wear, helping extend service life and optimize maintenance intervals.
Q 87: Under what conditions is lube oil considered deteriorated?
Ans: Lube oil is considered deteriorated when TBN, viscosity, and flash point decrease, while oxidation, water content, insolubles, and dispersancy increase.
Q 88: What challenges arise in cast iron welding?
Ans: Challenges in cast iron welding include brittleness, high carbon content, close grain structure, poor thermal conductivity, and risks of stress and distortion.
Q 89: What is the purpose of the elliptical shape of a manhole door?
Ans: An elliptical manhole door minimizes opening size, reducing stress concentration while allowing easier entry. This shape also aligns with vessel stresses, requiring less material and weight than other shapes.
Q 90: What environmental issues are associated with using CFCs?
Ans: CFCs release chlorine atoms that deplete the ozone layer, allowing harmful UV radiation through. They also trap heat, contributing to global warming.
Q 91: What is a pH value?
Ans: pH is the logarithmic measure of hydrogen ion concentration in a solution, indicating acidity or alkalinity. A pH < 7 is acidic, > 7 is basic.
Q 92: How can fuel oil viscosity be maintained if the viscotherm is absent or damaged?
Ans: Use the fuel analysis report and a viscosity nomogram to determine required heating. Manually adjust steam to the fuel heater, closely monitoring steam pressure and fuel outlet temperature.
Q 93: What causes discrepancies between helm order and the steering gear’s local angle display?
Ans: Discrepancies can be due to air in the hydraulic system, faulty or stiff buffer springs, defective instruments, or worn linkages.
Q 94: What is the purpose of accumulators in hydraulic systems?
Ans: Accumulators absorb shock from load changes, maintain circuit pressure, and supplement pump flow during peak demands, storing charge during low-demand periods.
Q 95: How does crosshead slipper lubrication work?
Ans: Lubricating oil is supplied to the guide shoes through pipes from the main lube oil system or via drilled passages in the pin to the slipper faces.
Q 96: How do you determine when it’s safe to re-enter the engine room after CO2 flooding?
Ans: Safety for re-entry depends on fire heat and duration, fire status, ship’s position and condition, entry point location, and risk analysis results.
Q 97: What materials are used for CO2 bottles and their accessories?
Ans: CO2 bottle: seamless manganese steel
Cable: phosphor bronze
Seal/bursting disc: 0.3mm phosphor bronze
Pipeline: galvanized mild steel
Siphon tube: copper
Cutter: 120°, 19mm travel
Q 98: What is the quality of vapor returning to the compressor suction in the refrigeration system, and how do you ensure sufficient superheat?
Ans: The vapor should have adequate superheat. This is verified by comparing the return vapor pressure and temperature from the P-T chart with the evaporator outlet temperature; superheat is the temperature difference between these readings.
Q 99: What is the material of the tie rod?
Ans: High tensile steel
Q 100: What is the material of the foundation bolts?
Ans: High tensile steel
Conclusion
In the dynamic world of marine engineering, mastering both theory and practice is essential. “Marine Engineering: The Best Marine Engineering Q&A of 24-25” serves as a valuable resource for professionals and students alike, providing up-to-date insights on key topics like engine maintenance, safety protocols, and propulsion systems. This guide empowers marine engineers with clear explanations and practical knowledge, equipping them to tackle challenges confidently. Whether preparing for exams or enhancing skills on the job, this Q&A collection is an indispensable tool for success in the evolving maritime industry.
