The SQUAT phenomenon occurs when a vessel moves through shallow water, creating a venturi effect that increases the ship's draft. This results in higher engine load and reduced steering ability due to the vacuum created under the hull.

The firing order helps balance primary and secondary inertia forces, optimizes exhaust grouping, distributes stress evenly along the crankshaft, ensures proper bearing loading, and provides consistent firing intervals for smooth engine operation.

A thermostatic expansion valve regulates the flow of refrigerant from the high-pressure to the low-pressure side of a refrigeration system. This pressure drop lowers the refrigerant's evaporating temperature below that of the evaporator. It prevents liquid refrigerant from returning to the compressor and ensures automatic expansion control while maintaining a superheat of 6-7°C.

The L.P (Low Pressure) controller stops the compressor when the suction pressure drops, typically caused by the closure of compartmental solenoids. When the pressure in the compressor's suction rises due to the solenoid reopening, the L.P controller restarts the compressor, ensuring efficient system operation.

The L.P (Low Pressure) cutout protects the compressor by shutting it down when suction pressure drops too low, often due to refrigerant loss or blockage. This prevents air and moisture from entering the system if the pressure falls below atmospheric levels.

Lube oil in a refrigeration system serves multiple functions:

• Provides lubrication
• Seals clearance spaces between the discharge and suction sides of the compressor
• Acts as a coolant
• Actuates capacity control
• Reduces noise generated by the compressor.

Foaming occurs when refrigerant dissolved in the oil rapidly boils out due to a sudden pressure drop. When the compressor starts, excess refrigerant boiling out can be carried through the system. Key causes include:

• Liquid in the suction line (e.g., TEV stuck open, incorrect superheat setting, sensing bulb issues, overcharge)
• Crankcase heater malfunction
• High compressor capacity at startup
• Expansion valve providing too little superheat
• Insufficient oil charge

Concentric springs are used to prevent valve surging, which occurs when the spring's natural vibration frequency matches the camshaft speed. By using two springs, one inside the other, with different vibration characteristics, surging is minimized. Additionally, these springs reduce valve rotation, as their opposing forces counteract each other, enhancing stability and reducing wear. If one spring fails, the other continues to hold the valve, preventing damage from piston contact. This design also allows for thinner springs and meets stiffness requirements in limited space, with the total stiffness being the sum of both springs.

Starting air overlap ensures positive starting in the correct direction, allows the engine to start from any position, and provides redundancy so the engine can still start if one valve malfunctions.

Ovality refers to the distortion of the crank pin due to the combined effects of reduced lubrication effectiveness and directional thrust from the connecting rod. This distortion is most pronounced around 45 degrees after top dead center (ATDC) and can result from uneven loading of engine units or overloading. The maximum allowed ovality is 1/4th of the bearing clearance.

Ovality can be corrected through in-situ grinding and polishing, with a reference taken from the crank web fillet. The maximum allowable grinding is 2mm, as grinding beyond this limit reduces surface hardness significantly. Ovality, along with bearing clearance issues and poor lubrication, can lead to bottom bearing damage.

Critical temperature is the temperature above which a gas cannot be liquefied, regardless of the pressure applied during isothermal compression. .

Critical pressure is the pressure required to liquefy a gas at its critical temperature. .

A coalescer is a device with a material surface that causes small liquid droplets, such as oil, to combine into larger droplets. .

This process is known as coalescing. .

Constant tension winches use variable capacity pumps with constant pressure and horsepower control. The pump automatically adjusts across neutral to maintain constant system pressure, ensuring steady motor torque when both drawing in and paying out, providing consistent tension. .

Reduced fuel quantity leads to loss of power and affects cylinder liner lubrication.

Imbalance in power output among engine units.

High exhaust temperatures and smoky emissions

Injection timing delays, causing late injection Afterburning issues

Significant loss of cylinder power

Short circuit trip for protection

Self-starts after a power failure

High temperature alarm to prevent overheating

200% motor insulation for enhanced safety

Overload alarm to detect excessive load

Alarm for phase failure

One steering motor connected to the emergency bus Hydraulic Safeties

Low-level cutout to prevent damage

High lube oil temperature cutout for protection

Limit switches prevent excess movement in all directions

Overload trip to safeguard against excessive load

Dead man’s handle for controlled operation

Guards over pulleys to prevent accidents

Locking device on the lifting hook for secure operation

Mechanical locking to prevent movement in rough weather

One steering motor connected to the emergency bus Hydraulic Safeties

Low-level cutout to prevent damage

High lube oil temperature cutout for protection

Blocked air intake filter or fouled turbocharger

Sudden reduction in engine load

Restricted exhaust or air passages, such as clogged scavenge ports, valves, or air coolers

Malfunctioning fuel system, such as a misfiring unit

Unbalanced engine output, damaged exhaust valves, or scavenge fires

Electromagnetic braking system

Prevents automatic restart

Protection against motor overload

Delay timer for restarting

Manual Safeties:

Torque-limiting slipping clutch

Pressure relief valve

Hand-operated or mechanical brake

Chain stopper for securing

Relief valve to release excess pressure

Fusible plug for temperature protection

Drain to remove accumulated moisture

Low-pressure alarm for early detection

Ineffective cooling water flow

Scale buildup in the cooling system

Excessive temperature fluctuations causing high thermal gradients

Uneven tightening of bolts or fuel valves

Engine overloading or racing

Corrosion from gas or acid due to leaky exhaust valves

Faulty relief valves

Corrosion on the water side of the cylinder head

Increased stroke length capability

Simple liner construction

No need for long piston skirts

High scavenging and thermal efficiency

Uniform wear on piston rings and liners

Reduced thermal stresses

Effective burning of low-grade fuel

Minimal intermixing of scavenging air with exhaust gases

Exhaust valve opens late for more work and closes early to maximize scavenging air use

The relief valve is typically set 10-14.5% above the working pressure, around 120 bar, slightly higher than the maximum operating pressure.

Use higher viscosity oil

Maintain a low head pressure

Replenish oil regularly to compensate for losses

Periodically drain off water

Reverse the shaft direction to dislodge foreign particles

Thermal stresses caused by cold starting air and scavenging air

Casting defects during manufacturing

Scavenge fire incidents

Overheated piston due to cooling failure or cooling side deposits from oil oxidation

After burning in the combustion chamber

Faulty fuel injection system causing excessive penetration or poor atomization

Critical speed can lead to resonance, torsional vibrations, and fatigue failure of components.

It can be mitigated by:

Vibration dampers

Detuners

Electric vibration compensator units

Inject air into the evaporator shell

Close the distillate pump outlet, vacuum breaker valve, bottom blow-off valve, and feed water valve

Maintain shell pressure at around 1.0 bar gauge

Apply soap solution to joints, packings, and suspected leak areas

Corrosive wear, especially acidic corrosion from combustion byproducts

Fuel impingement leading to deposits

Exposure to high temperatures from combustion gases

Piston direction change causing step-like wear at the reversal point

Lubrication loss in low-speed diesel engines

Low compression leading to poor combustion

Faulty injection system causing incomplete combustion

Insufficient scavenging air

Clogged or fouled exhaust system

Broken piston rings

Ineffective lube oil seals

After burning or use of bad fuel, along with fuel-related faults

Faulty cylinder lubrication

During starting, black smoke is common due to: fixed starting fuel index, low air, slow piston speed, cold combustion chamber, and low fuel injection pressure

Types of vibration:

Torsional vibration

Linear vibration

Resonant vibrations, which may involve either or a combination of both

The most harmful is torsional vibration, as it primarily impacts the crankshaft and propeller shafting.

Forcing frequency, in relation to crankshafts:, is caused by firing impulses from the cylinders. These impulses combine to form complex waveforms, represented by harmonics:

1x cycle frequency: first-order harmonic

2x cycle frequency: second-order harmonic

3x cycle frequency: third-order harmonic, and so on.

A node is a point in a vibrating medium where deflection is zero and the amplitude changes direction. More nodes in a given length indicate a higher natural frequency.

An electric compensator, typically located in the steering gear compartment where deflections are greatest, neutralizes external forces or moments by synchronizing with the correct phase. It requires additional seating for installation to maximize its effect. .

Stiff connections (links) : Equipped with friction plates to adjust based on the ship’s loading conditions Hydraulic top bracing: Raises the natural frequency to prevent resonance within the engine’s normal operating speed range.

Balancing controls vibrations by ensuring that out-of-balance forces and couples are either canceled out or minimized to an acceptable level..

A 1st order moment acts in both vertical and horizontal directions. In engines with five or more cylinders, it generally has little impact, but in four-cylinder engines, it can be significant. Resonance with the 1st order moment may occur with hull vibrations involving two or three nodes. A 1st order compensator, consisting of two counter-rotating masses at crankshaft speed, can be added to the chain tightener wheel to counteract these effects.

A second order moment affects only the vertical direction and is relevant for 4, 5, and 6-cylinder engines. Resonance with this moment may occur in hull vibrations with more than three nodes. A second order moment compensator, consisting of two counter-rotating masses, operates at twice the engine speed to counteract these effects..

Axial vibrations in the crankshaft occur when gas pressure on the crank throw, via the connecting rod, causes axial deflection. These vibrations can transfer to the ship’s hull through the thrust bearing. The remedy is to use axial dampers to reduce these vibrations.

Torsional vibrations arise from fluctuating gas pressure during the working cycle and the crankshaft/conrod mechanism, creating varying torque. Propeller interactions with the uneven wake field also contribute to these vibrations..

Remedy: Adjust crankshaft diameter to modify its natural frequency or use a torsional damper.

Cavitation on the impeller

Friction, leakage losses, loss of suction head, clogged suction filter, worn wear ring, or air ingress in the suction side

Low voltage supplied to the pump motor

Poor maintenance or incorrect reassembly after overhaul

When resonance occurs, the following modifications can be made

Lanchester balancers: Installed on the engine or as electrically driven units in the steering flat to compensate for ship vibrations caused by the second-order vertical moment.

Counterweights on the crankshaft: Adjusted to counter first-order vibrations.

Primary and secondary balancers: Combined to manage both types of vibrations.

Adjusting side stays: To help minimize the effects of vibration.

Unbalanced external moments

Guide force moments affecting engine dynamics

Axial vibrations in the shafting system

Torsional vibrations within the shafting system

Unbalanced external moments

Guide force moments affecting engine dynamics

Axial vibrations in the shafting system

Torsional vibrations within the shafting system

Modify shaft sizes

Change the number of propeller blades

Adjust the firing order

Implement viscous or other dampers

Use balancing weights

Detune the coupling

Guide force moments originate from the angularity of the connecting rod and are caused by transverse reaction forces on the crosshead. These moments result in engine vibrations around the foundation bolts. There are two types:

H moment: Causes a rocking motion of the engine top arthwartships.

X moment: Leads to a twisting motion of the engine.

Over-critical running occurs when the natural frequency of one-node vibration is adjusted so that resonance with the main critical order happens 30-70% below the engine’s MCR. Characteristics of this system include:

High-inertia turning wheel

Barred speed range of approximately +/- 10% around the critical engine speed

A turning wheel may be required on the crankshaft

Small-diameter shaft (material with high UTS required)

Under-critical running occurs when the natural frequency of one-node vibration is adjusted so that resonance with the main critical order happens 35-45% above the engine’s maximum continuous rating (MCR).

Characteristics of an under-critical system include:

Short shafting system

Large shaft diameter

Low-inertia turning wheel or no turning wheel

No barred speed range

Ventilate the tank using a blower, ensuring cross ventilation with at least two openings for air entry and exit.

Empty the oil and, if necessary, strip with portable pumps.

Clean the tank with seawater and pump the contents through the oily water separator.

Test for explosive gases at multiple points, especially in the corners and bottom of the tank.

Complete the necessary checklist and obtain required certificates for the inspection.

There’s a risk of air leaking in, contaminating the refrigeration system.

Oxygen is absent in the compressor crankcase.

The refrigerant’s low temperature reduces the likelihood of hot spots.

As the crankcase acts as the compressor’s suction chamber, there’s a chance it could draw in air and moisture.

To maintain oil viscosity for effective lubrication.

To prevent refrigerant and oil separation issues at low temperatures, reducing oil carryover.

To avoid the lube oil reaching its floc point, which could lead to passage narrowing or blockage due to flocculation.

Dip tubes ensure that only liquid CO2 is drawn during release, which expands into gas after passing through the nozzles. This prevents freezing and blockage while achieving 85% discharge within 2 minutes, as the liquid represents a larger gas volume.

The compression ratio is the ratio of the total volume (swept volume + clearance volume) to the clearance volume.

Brake thermal efficiency is the ratio of energy developed at the brake to the energy supplied, comparing the heat liberated during combustion to the energy output at the brake.

Supercharged engine: Efficiency can reach up to 4.0

2-stroke engine: Efficiency ranges between 0.85 and 2.5

Naturally aspirated engine: Efficiency typically ranges from 0.85 to 0.95

Volumetric efficiency is the ratio of the actual volume of air drawn into the compressor to the swept volume

Shaft misalignment, worn bearings, loose foundation bolts, improper hydraulic clearances, damaged coupling bolts/seating, worn bottom bush, debris buildup, and corrosion or erosion on rotating parts.

A back pressure valve, located at the evaporator coil exit in multi-temperature systems, maintains system balance by managing pressure differences. It ensures liquid refrigerant is prioritized for compartments requiring lower temperatures and acts as a spring-loaded non-return valve.

The H.P cut-out is a safety device on the compressor’s discharge side, tripping the compressor if the high-pressure side exceeds the normal operating limit.

Driers in the liquid line absorb moisture from the refrigerant using a renewable cartridge filled with activated alumina or silica gel, ensuring efficient system operation. It also includes a charging connection.

A solenoid valve, controlled by the thermostat, is placed in the liquid line before the thermostatic expansion valve. It shuts off refrigerant flow when the compartment reaches the lower temperature set point and opens when the temperature rises above the upper set point.

Oil-cooled stern tube bearing: Clearance ranges from 1.87 to 2.0 mm

Water-cooled stern bearing: Clearance is typically 8.0 mm (range 8 to 12 mm)

The standard propeller drop is typically 1 mm for every 160 mm of shaft diameter.

Wiping damage on the bearing surface

Fatigue failure, resulting in cracks

Tin oxide encrustation (black SnO₂ formation)

Tearing of the overlay layer

Acidic corrosion leading to surface damage

Cavitation and erosion of the bearing material

Dross inclusion within the bearing

Spark erosion causing localized damage

Bacterial attack with honey-colored deposits on the surface

Better heat transfer due to reduced thickness and uniform contact with the housing

Increased mechanical properties for better performance

High load carrying capacities to handle heavy loads

Fatigue resistance for longer bearing life

No bedding required, simplifying installation

Conformability and embed ability for better adaptability

Lightweight, easy to fit, and store

Advantages:

Excellent low-temperature fluidity and pump ability due to no wax content

Better oil retention at high temperatures

Lower friction losses, enhancing efficiency

Reduced thickening during use from oxidation resistance

Fewer deposits at high temperatures thanks to thermal stability and oxidation resistance

Disadvantages:

Higher cost, approximately 6-12 times more expensive

Limited availability in some regions

Uses:

Air compressors

Purifiers

Hydraulic units

Assess contaminant levels to evaluate contamination rates and the effectiveness of purification

Monitor deterioration in lube oil properties or additives to ensure suitability for continued use

Predict internal wear rates on machinery components

Extend time between overhauls or surveys, improving maintenance intervals

Increased water content

Reduction in TBN (Total Base Number)

Decreased viscosity

Lower flash point

Increased oxidation levels

Higher insolubles content

Increased dispersancy

High carbon content in the form of graphite

Brittleness, making it prone to cracking

Close grain structure, complicating the welding process

Poor thermal conductivity, leading to uneven cooling

Potential for stresses and distortion during welding

Governor: Regulates the overall engine speed.

Flywheel: Manages cyclic RPM fluctuations. Flywheel relies solely on inertia, while the governor uses inertia to adjust fuel linkages and stabilize RPM changes.

Tie rods maintain the engine structure under compression, which:

Increases fatigue strength, as tensile stress is the primary cause of fatigue

Maintains alignment of the running gear to prevent fretting

During firing, forces attempt to push up the cylinder covers and press down the bearing saddle, inducing tensile stress.

Tie rods are tightened to keep the engine structure in compression, even under peak firing conditions, preventing tensile loading.

A thrust bearing is installed at one main bearing location if the coupling lacks a thrust housing. White metal rings or a small collar are added to control axial movement, allowing minimal clearance between the shaft and adjacent webs. Only one such bearing is used per shaft to avoid issues from differential thermal expansion between the frame and crankshaft.

Tie rods are placed near the crankshaft centerline to minimize bending moments on transverse girders during firing, reducing distortion of the bearing housing caused by crankshaft forces on the cylinder head.

Align the engine: Rotate the engine to align a mark on the liner with the stern tube, or position unit 1 at TDC. Alternatively, use a designated propeller blade (A, B, C, D, etc.) facing upwards.

Take poker gauge readings: Compare these with previous measurements.

Bearing clearances: 2 mm for oil-sealed, 8 mm for seawater-lubricated systems.

Bearing lengths: 2x shaft diameter for oil-cooled, 4x shaft diameter for seawater-lubricated systems.

Ozone depletion: CFCs, when released, undergo pyrolysis and release chlorine atoms, which catalytically destroy the ozone layer. This ozone layer in the stratosphere acts as a shield against harmful UV radiation.

Global warming: CFCs, along with other greenhouse gases, trap radiation from the Earth’s surface, contributing to the greenhouse effect and global warming.

pH is the logarithm of the reciprocal of the hydrogen ion concentration in a solution. Pure water at 25°C has equal concentrations of hydrogen and hydroxyl ions (10⁻¹⁴ g ions/L). A solution is basic if hydroxyl ions exceed hydrogen ions and acidic if the opposite. The pH formula is: pH = log [1/H⁺]. Higher temperatures increase hydrogen ion concentration, raising acidity.

Refer to the fuel oil analysis report for viscosity data at 50°C and desired injection viscosity. Use a viscosity nomogram to determine required heating. Manually adjust steam inlet to the fuel oil heater, closely monitoring steam pressure and outlet temperature to maintain proper viscosity.

Achieves isothermal compression: Intercooling reduces the work needed for compression.

Lowers outlet temperature: Prevents lube oil oxidation and ensures better lubrication.

Reduces deposits: Minimizes buildup in the air system.

Increases air density: Allows smaller HP compression chambers.

Removes moisture: Intercooling facilitates moisture condensation and removal.

Even load distribution: Staging the compression ensures balanced loads throughout the cycle.

Elliptical openings in pressure vessels are smaller than circular ones, minimizing material removal while allowing entry. The smooth, rounded edges reduce stress concentration, unlike rectangular or square shapes. A doubler ring is added around the opening to compensate for material loss, with its thickness based on the axis length and shell thickness. The minor axis is aligned with the vessel's length, where stress is highest, optimizing weight and material savings.

Longitudinal stress: Pd/2t

Circumferential stress: Pd/4t

Insufficient lubrication: Low lube oil pressure can cause the compressor to trip, and moving parts may suffer damage due to inadequate lubrication.

Cooling issues: The shaft-driven cooling water pump may not generate enough flow, leading to a trip due to insufficient water flow or high air temperature.

Minimizes misalignment and vibration: Direct misalignment or motor vibration could lead to shaft seal leaks and refrigerant loss, so a belt drive helps reduce this risk.

Limits damage from liquid entry: In case of liquid entry into the compressor, the belt can slip, reducing potential damage due to its flexibility.

Worn out linkages: Affecting accurate transmission of movement

Air in hydraulic telemotor: Leading to improper signal transmission

Buffer spring issues: Weak or stiff spring, or faulty hunting gear disrupting responsiveness

Instrument errors: Defects causing inaccurate readings

Vapor quality requirements:

• • Must have sufficient superheat when returning to compressor suction line
• • Verify superheat using refrigerant's P-T chart (compare vapor pressure/temperature with evaporator outlet temperature)
• • Superheat = Difference between actual temperature and saturation temperature
• • Prevents liquid slugging and ensures proper compressor operation

Key functions of hydraulic accumulators:

• • Shock absorption: Dampens impact from load variations or sudden flow changes
• • Pressure maintenance: Compensates for leaks and thermal pressure fluctuations
• • Peak demand support: Supplements pump capacity during high-demand periods
• • Energy storage: Stores hydraulic energy during low-demand for later use
• • Emergency power: Provides backup power source during pump failure

Crosshead slipper lubrication methods:

• • Direct feed system: Lubricating oil supplied via dedicated pipe from main lube oil system
• • Pin passage lubrication: Oil fed through drilled passages in the crosshead pin to slipper faces
• • Wedge film formation: Creates hydrodynamic lubrication during operation
• • Pre-lubrication requirement: Must be primed before engine startup

Critical Safety Protocol:

• • Mandatory Cooling Period: Minimum 30 minutes post-discharge (SOLAS Reg. II-2/10)
• • Atmospheric Verification: O₂ > 19.5%, CO₂ < 5%, toxic gas clearance
• • Thermal Assessment: IR scan for hotspots (>65°C threshold)
• • Structural Evaluation: Bulkhead integrity and stability check
• • Entry Team Requirements: 3 personnel minimum (BA sets + fire proximity suits)
• • Ventilation Protocol: Forced-draft ventilation for 15 minutes prior
• • Emergency Backup: Rescue team on standby during entry

Liner material: Typically nodular cast iron, designed for longitudinal expansion with minimal circumferential expansion. Alloying elements like vanadium and titanium enhance specific properties.

Piston ring material: Made from harder graphite grey cast iron, often alloyed with chromium, nickel, or copper for improved performance.

Principal Differences:

• Piston rings are harder than liners as they endure continuous wear, whereas only part of the liner is worn.
• Piston rings flex circumferentially, crucial for running in, sealing combustion gases, and conforming to the liner's surface.

Stainless steel resists corrosion due to a protective chromium oxide film that forms spontaneously when exposed to air or aerated water. Without this film, its corrosion resistance is only slightly better than regular steels.

Old engines: 0.1mm/1000 hours

Modern 2-stroke engines: 0.03mm/1000 hours

Modern 4-stroke engines: 0.12mm/1000 hours

Achieved by:

• Highly alkaline lube oil
• Load-dependent jacket cooling water temperature control
• Improved cast iron quality with hard facing
• Optimized piston ring profile design
• Enhanced lube oil formulations
• Multilevel cylinder lubrication
• Condensate separation from scavenging air
• Use of anti-polishing rings or piston cleaning techniques

Needle: High-speed steel

Body: Case-hardened steel