Ship Construction Flashcards
Describe the function of EACH of the following components of a diesel engine:
chocks; (4 marks)
bedplate; (4 marks)
tie rods; (4 marks)
entablature. (4 marks)
Functions of Diesel Engine Components
- Chocks (4 Marks)
• Chocks are solid blocks, usually made of cast steel or resin-based materials, placed between the engine bedplate and the ship’s foundation.
• They ensure proper alignment and secure the engine to the hull, preventing movement due to vibrations or dynamic forces.
• Chocks help distribute the engine’s weight evenly, reducing stress on the structure.
• They play a crucial role in maintaining the integrity of the propulsion system by preventing misalignment.
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- Bedplate (4 Marks)
• The bedplate is the foundation of the diesel engine, supporting all major components such as the crankshaft, main bearings, and frames.
• It is typically made of cast steel or fabricated welded steel to provide strength and rigidity.
• The bedplate absorbs and distributes operational stresses, preventing excessive vibrations and structural damage.
• It houses the main bearing pockets and ensures accurate alignment of the crankshaft.
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- Tie Rods (4 Marks)
• Tie rods are long, high-tensile steel bolts that pass through the engine structure, connecting the bedplate, frame, and entablature.
• Their primary function is to hold these components together under compressive stress, reducing the load on transverse bolts.
• They help prevent misalignment and reduce the risk of structural failure due to thermal expansion or dynamic forces.
• By distributing loads efficiently, tie rods minimize the risk of fatigue failure in large marine engines.
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- Entablature (4 Marks)
• The entablature is the upper section of the diesel engine frame, supporting the cylinder block and housing the cooling and lubrication passages.
• It provides structural rigidity and alignment for the cylinders, ensuring efficient combustion.
• The entablature contains passages for fuel, lubricating oil, and cooling water, ensuring proper engine operation.
• It helps to distribute combustion forces evenly, transferring them through the tie rods to the bedplate, reducing stress on individual components.
Describe the function of EACH of the following components of a diesel engine:
chocks; (4 marks)
- Chocks (4 Marks)
• Chocks are solid blocks, usually made of cast steel or resin-based materials, placed between the engine bedplate and the ship’s foundation.
• They ensure proper alignment and secure the engine to the hull, preventing movement due to vibrations or dynamic forces.
• Chocks help distribute the engine’s weight evenly, reducing stress on the structure.
• They play a crucial role in maintaining the integrity of the propulsion system by preventing misalignment.
Describe the function of EACH of the following components of a diesel engine:
bedplate; (4 marks)
Describe the function of EACH of the following components of a diesel engine:
bedplate; (4 marks)
- Bedplate (4 Marks)
• The bedplate is the foundation of the diesel engine, supporting all major components such as the crankshaft, main bearings, and frames.
• It is typically made of cast steel or fabricated welded steel to provide strength and rigidity.
• The bedplate absorbs and distributes operational stresses, preventing excessive vibrations and structural damage.
• It houses the main bearing pockets and ensures accurate alignment of the crankshaft.
Describe the function of EACH of the following components of a diesel engine:
tie rods; (4 marks)
- Tie Rods (4 Marks)
• Tie rods are long, high-tensile steel bolts that pass through the engine structure, connecting the bedplate, frame, and entablature.
• Their primary function is to hold these components together under compressive stress, reducing the load on transverse bolts.
• They help prevent misalignment and reduce the risk of structural failure due to thermal expansion or dynamic forces.
• By distributing loads efficiently, tie rods minimize the risk of fatigue failure in large marine engines.
Describe the function of EACH of the following components of a diesel engine:
entablature. (4 marks)
Describe the function of EACH of the following components of a diesel engine:
entablature. (4 marks)
- Entablature (4 Marks)
• The entablature is the upper section of the diesel engine frame, supporting the cylinder block and housing the cooling and lubrication passages.
• It provides structural rigidity and alignment for the cylinders, ensuring efficient combustion.
• The entablature contains passages for fuel, lubricating oil, and cooling water, ensuring proper engine operation.
• It helps to distribute combustion forces evenly, transferring them through the tie rods to the bedplate, reducing stress on individual components.
Question 8 (16 Marks)
a. Explain, with reference to stability, why, when the vessel has full bunkers, fuel stored in higher tanks, is generally used before fuel stored in lower tanks. (16 marks)
a. Explain, with reference to stability, why, when the vessel has full bunkers, fuel stored in higher tanks is generally used before fuel stored in lower tanks. (16 marks)
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- Center of Gravity and Stability (4 marks):
• A vessel’s stability depends largely on the vertical position of its center of gravity (G).
• The higher the center of gravity, the lower the metacentric height (GM), resulting in poorer stability.
• Using fuel from higher tanks lowers the center of gravity over time, improving GM and thus enhancing stability.
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- Free Surface Effect (4 marks):
• Tanks that are only partially filled create a free surface effect, which reduces stability by shifting the center of gravity as the liquid moves.
• High-level tanks with large free surfaces can drastically reduce GM, so using them early helps eliminate their negative effect sooner.
• Once emptied or fully pressed up (full), the free surface effect from that tank is removed.
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- Rolling and Heel Resistance (2 marks):
• A lower center of gravity provides a more powerful righting lever (GZ), increasing the vessel’s ability to resist heeling and rolling.
• This is especially important in rough weather or during cargo operations, where stability margins are crucial.
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- Trim and Stress Considerations (2 marks):
• Using higher fuel tanks first also helps avoid undesirable trim or hull stress, especially if tanks are located fore or aft.
• Reducing weight higher in the ship prevents excess bending moments or shear forces.
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- Regulatory Compliance and Best Practice (2 marks):
• Stability requirements under SOLAS and class rules emphasize maintaining adequate positive GM and minimizing free surface effect.
• Following proper fuel consumption sequence aligns with stability management and safety best practices.
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- Summary (2 marks):
• In summary, fuel from higher tanks is used first to lower the center of gravity, improve GM, reduce free surface effect, and enhance overall stability and safety of the vessel.
With reference to the ship’s structural arrangements, explain, with the aid of skecth, EACH of the following terms:
a) Sheer (4Marks)
b) Flare (4Marks)
c) Camber (4Marks)
d) Tumblehome (4Marks)
- Sheer (4 Marks)
Explanation:
• Sheer refers to the upward longitudinal curvature of a ship’s deck from midship towards the bow and stern.
• It improves seakeeping, helping reduce water shipping on deck, and enhances strength and aesthetics.
Sketch Tip:
• Side profile of a ship showing a curved deck line rising toward the bow and stern.
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- Flare (4 Marks)
Explanation:
• Flare is the outward curvature of the ship’s hull above the waterline, especially in the bow area.
• It helps deflect waves, reducing spray on deck and improving buoyancy in head seas.
Sketch Tip:
• Front view (bow-on) showing the hull widening above the waterline.
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- Camber (4 Marks)
Explanation:
• Camber is the transverse upward curvature of the main deck, highest at the centerline and sloping toward the sides.
• Aids in drainage of water off the deck and adds deck strength.
Sketch Tip:
• Cross-section of the deck showing a gentle arch from side to side.
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- Tumblehome (4 Marks)
Explanation:
• Tumblehome is when the ship’s sides slope inward above the waterline, opposite of flare.
• Historically used for military vessels to reduce target profile or to support turret arrangement.
Sketch Tip:
• Cross-sectional view of the hull where the upper part of the sides slope inward toward the centerline.
With reference to the ship’s structural arrangements, explain, with the aid of skecth, EACH of the following terms:
a) Sheer (4Marks)
b) Flare (4Marks)
c) Camber (4Marks)
d) Tumblehome (4Marks)
With reference to main distribution systems fitted with preference trips:
(a) state why the preference trip is fitted.
(b) explain the operation of a THREE stage trip.
(c) state THREE circuits that can not be connected to the preference trip giving a reason for
EACH (6)
- Why the Preference Trip is Fitted (2 marks)
• Purpose:
A preference trip is fitted to prevent total blackout by shedding non-essential loads when the electrical load exceeds the generator capacity.
• Explanation:
It ensures the electrical system remains stable and operational by prioritizing essential services and avoiding generator overload or tripping.
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- Operation of a THREE-Stage Trip (4 marks)
A three-stage preference trip system disconnects loads in a priority-based sequence:
1. First Stage – Non-Essential Load Shedding:
• Trips comfort or hotel loads (e.g. air conditioning, laundry) when load approaches generator capacity.
2. Second Stage – Semi-Essential Load Shedding:
• Disconnects auxiliary machinery (e.g. ballast pumps, deck machinery) if overload persists after first stage.
3. Third Stage – Emergency Load Shedding:
• Trips additional circuits or starts standby generator if system is still overloaded, preventing total generator trip.
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- THREE Circuits That Cannot Be Connected to the Preference Trip (6 marks – 2 marks each)
- Steering Gear:
• Reason: Essential for navigational safety; required to be operational at all times under SOLAS. - Main Propulsion Control Systems:
• Reason: Loss of propulsion control could lead to loss of maneuverability, posing a collision or grounding risk. - Fire Detection and Alarm Systems:
• Reason: Critical for crew and ship safety; must remain active to detect and respond to fire hazards.
- Steering Gear:
With reference to electrical motors:
a. state the routine maintenance that is necessary: (8 marks)
b. describe the tests carried out to prove good electrical condition. (8 marks)
(a) Routine Maintenance Necessary (8 marks – 1 mark each for 8 points)
1. Clean external casing and air vents – to ensure proper cooling and prevent overheating.
2. Inspect and clean the commutator or slip rings – to maintain good contact and reduce sparking.
3. Check and clean brushes – ensure correct brush pressure and that they are not worn down.
4. Lubricate bearings – using correct grade and quantity of grease or oil to avoid wear or overheating.
5. Check for abnormal noise or vibration – may indicate worn bearings or misalignment.
6. Tighten terminal connections – to prevent loose connections and arcing.
7. Inspect insulation and wiring for damage – to detect early signs of deterioration or overheating.
8. Check motor mounting and alignment – to avoid mechanical stress and coupling issues.
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(b) Tests to Prove Good Electrical Condition (8 marks – 2 marks each for 4 tests)
1. Insulation Resistance Test (Megger Test):
• Measures resistance between windings and earth.
• High resistance (usually >1 MΩ) indicates good insulation.
2. Continuity Test:
• Confirms winding continuity and absence of open circuits.
• Ensures current can flow properly through motor windings.
3. Earth Fault Test:
• Detects leakage paths from windings to the motor casing.
• Ensures safety by confirming there’s no fault to earth.
4. No-Load Test Run:
• Motor is run without load to observe smooth operation, noise, vibration, and current draw.
• Confirms mechanical and electrical health under basic conditions.
With reference to lubricating oil or fuel oil tanks that have ventilators on the vessels main weather deck, explain EACH of the following:
a. the purpose of the ventilation; (4 marks)
b. how ingress of sea water in bad weather is prevented; (4 marks)
c. how the risk of fire entering the ventilator is reduced; (4 marks)
d. how the risk of pollution is reduced. (4 marks)
Lubricating Oil or Fuel Oil Tanks with Ventilators on the Vessel’s Main Weather Deck
- The Purpose of the Ventilation (4 marks)
The ventilation of lubricating oil or fuel oil tanks serves several critical purposes:
• Preventing Pressure Build-up: Ventilation ensures that air can flow in and out of the tank as the fuel or oil is consumed or added. This prevents the creation of a vacuum or excessive pressure inside the tank, which could damage the tank or cause difficulties in fuel transfer.
• Preventing Accumulation of Flammable Gases: By ventilating the tank, any potentially flammable vapors or gases (like from the evaporation of fuel oil or lubricating oil) are expelled. This reduces the risk of an explosion or fire inside the tank.
• Maintaining Safe Airflow: It allows for a safe and regulated flow of air to and from the tank to avoid contamination and ensure the proper functioning of the oil or fuel systems.
• Preventing Condensation: Proper ventilation also helps prevent condensation inside the tank. Without adequate ventilation, water can accumulate in the form of condensation, which could lead to the degradation of oil or fuel quality.
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- How Ingress of Sea Water in Bad Weather is Prevented (4 marks)
To prevent sea water from entering the ventilators during bad weather, the following methods are employed:
• Waterproof Ventilator Caps: Ventilators are equipped with caps or cowlings that are designed to shed water. These caps are often angled or designed with flaps that direct rainwater or spray away from the opening, preventing water from entering the tank.
• Non-Return Valves: Some ventilation systems use non-return valves that close off the air inlet if water is present. This mechanism helps prevent the ingress of sea water, especially in rough seas when water could otherwise splash or be forced into the vent.
• Positioning of Ventilators: Ventilators are positioned on higher parts of the vessel, usually on the weather deck, to minimize the risk of water ingress from waves or spray. Furthermore, they are sometimes fitted with cowls or deflectors to ensure water is directed away from the opening.
• Overflow Drains: Tanks are often equipped with overflow drains or other mechanisms that direct any water that does manage to enter the system to a safe drainage location, avoiding damage to the oil or fuel and the tank itself.
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- How the Risk of Fire Entering the Ventilator is Reduced (4 marks)
The risk of fire entering the ventilator is minimized through the following precautions:
• Flame Arresters: A flame arrester is a device installed in the ventilator system that prevents flames from traveling into the tank. It is designed to stop any fire that may occur outside the tank from entering the vent and igniting the flammable gases inside the tank.
• Ventilator Sizing and Positioning: Ventilators are designed to minimize the possibility of sparks or flames from the surrounding environment entering the tank. They are usually positioned away from potential sources of ignition, such as exhaust vents or other hot surfaces.
• Spark-Proof Materials: Ventilation systems and their components (e.g., pipes, covers, and caps) are often constructed from non-sparking materials to further reduce the risk of ignition.
• Vent Cap with Flameproof Design: The vent caps are often designed with features such as baffles or internal deflectors that reduce the likelihood of sparks or flames entering the ventilator. This design helps to stop any ignition sources from traveling into the tank.
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- How the Risk of Pollution is Reduced (4 marks)
The risk of pollution from oil or fuel tanks is minimized using the following strategies:
• Anti-Pollution Vent Valves: The tank ventilators are typically equipped with anti-pollution valves (also known as “oil-water separators”) that prevent the discharge of oil or fuel overboard if there is a spill or leakage. These valves close automatically when the liquid level reaches a certain point, preventing oil from escaping into the sea.
• Vent Filtration Systems: Some ventilation systems are equipped with filters or absorbers that can trap any oil droplets or fuel vapors, preventing them from being released into the atmosphere or escaping overboard.
• Closed Vent Systems: On many vessels, especially those following environmental regulations, closed venting systems are used to ensure that any fuel vapors or oil residues within the ventilator are not released into the atmosphere, reducing pollution risks.
• Regular Maintenance and Inspection: Regular inspection and maintenance of the ventilator and tank systems help detect potential leaks or damage that could lead to spills. Prompt repairs and the use of proper sealing techniques prevent pollutants from escaping into the environment.
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By implementing these measures, the vessel ensures safe and efficient handling of lubricating and fuel oil while minimizing environmental impact and reducing safety risks.
A- Molded depth
B- molded breadth
C-breadth extreme
D-upper tank bottom or molded beam
E-Double tank bottom
F-tumblehome
G-rise of floor
H-camber
Question 8 (16 Marks)
a. State the measurement that gives an indication of a ship’s stability. (2 marks)
b. Explain the meaning of the measurement stated in (a). (2 marks)
c. Explain how the measurement given in (a) indicates EACH of the following:
i. stable stability; (4 marks)
ii. unstable stability; (4 marks)
iii. neutral stability. (4 marks)
- State the measurement that gives an indication of a ship’s stability. (2 marks)
The measurement that gives an indication of a ship’s stability is the metacentric height (GM).
- Explain the meaning of the measurement stated in (a). (2 marks)
• Metacentric Height (GM) is the vertical distance between the center of gravity (G) of the ship and the metacenter (M). The metacenter is the point where the ship’s buoyant force acts when the ship tilts or heels. The metacentric height is a key indicator of the ship’s stability:
• A larger GM value indicates greater stability.
• A smaller GM value or a negative GM value indicates a risk of instability. - Explain how the measurement given in (a) indicates EACH of the following:
i. Stable Stability (4 marks)
• Stable stability occurs when the ship has a positive GM value (i.e., the metacenter is above the center of gravity).
• When the ship is tilted, the force of buoyancy acts through the metacenter, which creates a righting moment (restoring force) that pushes the ship back to an upright position.
• Effect: The greater the GM, the quicker and stronger the restoring force, which leads to stable stability. The ship will return to its upright position after a disturbance, ensuring safety and stability.
ii. Unstable Stability (4 marks)
• Unstable stability occurs when the GM value is negative (i.e., the center of gravity is above the metacenter). In this case, the metacenter is below the center of gravity.
• When the ship tilts, the force of buoyancy acts through a point below the center of gravity, causing a capsizing moment (a force that pushes the ship further away from its upright position).
• Effect: The ship becomes unstable and will continue to roll or tilt further away from the upright position. This can lead to capsizing or loss of control of the ship.
iii. Neutral Stability (4 marks)
• Neutral stability occurs when the GM value is zero (i.e., the metacenter is exactly at the same level as the center of gravity).
• When the ship tilts, the buoyancy force acts through the metacenter, but the restoring force is insufficient to return the ship to its upright position.
• Effect: The ship will not return to the upright position, nor will it continue to tilt indefinitely. Instead, it will remain at the new angle of tilt. This indicates neutral stability, where the ship will neither right itself nor capsize but will stay at an inclined angle.
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Summary:
• Stable Stability: Positive GM, ship returns to upright position.
• Unstable Stability: Negative GM, ship tilts further away from upright position (danger of capsizing).
• Neutral Stability: GM equals zero, ship remains tilted at an angle without returning to upright.
With reference to stresses and strain in vessels describe, with the aid of a sketch, the effect of EACH of the following:
(a) panting.
(4 marks)
(b) pounding. (4 marks)
(c) racking.
(4 marks)
(d) hogging.
(4 marks)
- Panting (4 Marks)
• Panting is a cyclic movement or flexing of the vessel’s hull due to the effect of waves striking the ship’s sides, typically in the fore or aft areas of the vessel.
• Effect: It causes localized deformation in the hull plating, especially in the forward sections, as a result of the pressure exerted by the waves on the hull.
• Sketch Description:
• Panting occurs when waves push against the ship’s hull, causing a repeated flexing (in and out movement) of the plates, especially at the bow area.
• The deformation can lead to stress concentration and possible damage to the hull structure if left unchecked.
Effect on Structure: Panting can lead to:
• Fatigue of the hull plating and structural components.
• Potential leakage or damage to the hull over time.
- Pounding (4 Marks)
• Pounding occurs when the vessel’s hull slams into the waves, particularly during heavy seas, causing a sudden shock or impact on the hull.
• Effect: It creates high localized stresses at the bow or other areas that come into contact with the waves. This can result in hull deformation, cracks, or structural damage in severe cases.
• Sketch Description:
• Pounding is characterized by the ship’s bow hitting the wave crest and the strong impact force acting on the ship’s structure.
• The bow compresses and flexes under the force of the wave, with the possibility of significant shock loading.
Effect on Structure:
• Potential cracking of the hull plates, especially in the forward sections.
• Stress concentration in localized areas, leading to structural damage if not managed.
- Racking (4 Marks)
• Racking refers to the deformation of a vessel’s hull caused by external forces, such as waves or wind, which results in the ship’s hull being twisted or distorted along its length.
• Effect: This twisting or shear force creates internal stresses in the vessel’s framework, particularly in the longitudinal direction. Racking typically occurs in rough seas and can affect the alignment of the ship’s structure.
• Sketch Description:
• Racking causes a twisting deformation of the hull where the ship’s sides bend in opposite directions (e.g., the port side may move inboard while the starboard side moves outboard).
• This results in shear forces acting on the hull plates and frames.
Effect on Structure:
• Can cause misalignment or weakening of the hull’s structure, especially in the frames and longitudinal members.
• Fatigue or cracking in areas where racking is most concentrated.
- Hogging (4 Marks)
• Hogging occurs when the ship’s hull is subjected to bending due to uneven distribution of weight, often caused by the vessel riding over large waves or an imbalance in load distribution.
• Effect: The hull experiences a bending moment, with the midship section rising and the bow and stern sections sinking, leading to tension at the top of the ship and compression at the bottom.
• Sketch Description:
• Hogging creates a concave shape (curved upward) of the ship’s hull, with the midsection elevated while the bow and stern sink.
• The bending stresses cause the ship’s structure to stretch in the middle and compress at the ends.
Effect on Structure:
• Increased stress on the keel and hull frames, leading to possible structural failure if the hogging stress is too great.
• Fatigue or damage to the hull plating, particularly in the midship area.
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Summary of Effects:
• Panting: Causes cyclic flexing of the hull, leading to localized deformation and fatigue.
• Pounding: Creates high-impact stresses at the bow, potentially leading to cracks or hull damage.
• Racking: Twisting deformation of the hull, leading to shear stresses and potential misalignment.
• Hogging: Bending of the hull, causing tension and compression that can lead to structural fatigue or failure.
These stresses are critical to understand for maintaining the structural integrity of a ship and ensuring safety during operation in rough seas.
Question 8 (16 Marks)
With reference to lubricating oil or fuel oil tanks that have ventilators on the vessels main weather deck, explain EACH of the following:
a. the purpose of the ventilation; (4 marks)
b. how ingress of sea water in bad weather is prevented; (4 marks)
c. how the risk of fire entering the ventilator is reduced; (4 marks)
d. how the risk of pollution is reduced. (4 marks)
- Purpose of the Ventilation (4 Marks)
The primary purpose of the ventilation system for lubricating oil or fuel oil tanks is to:
• Prevent Pressure Build-up: The ventilation helps maintain a balanced pressure inside the tank by allowing air to enter and exit as the oil level fluctuates due to temperature changes or consumption. Without proper ventilation, a vacuum or excess pressure could form, potentially causing damage to the tank structure or even a rupture.
• Prevent Gas Accumulation: Oils, especially fuel oils, can release volatile fumes or gases. Ventilation ensures that these gases are vented safely, reducing the risk of gas accumulation inside the tank, which could lead to hazardous conditions like fire or explosion.
• Maintain Tank Integrity: Proper ventilation allows the tank to “breathe,” reducing the chances of deformation or structural damage caused by pressure differences between the inside of the tank and the external environment.
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- How Ingress of Sea Water in Bad Weather Is Prevented (4 Marks)
In order to prevent sea water from entering the tanks during bad weather, the following measures are typically taken:
• Water-tight or Weather-tight Covers: Ventilators are often equipped with specially designed, weather-tight covers or cowls that shield the intake from rain, sea spray, or heavy waves. These covers prevent water from entering the ventilation system while still allowing airflow.
• Siphon Breaks: Some systems include siphon breaks or anti-siphon devices to prevent sea water from being sucked into the tanks if the ship rolls or pitches during rough seas. These devices stop water from entering the vent pipe when the ship is at a significant angle.
• High Placement of Vent Openings: Ventilators are often positioned higher on the ship’s weather deck, above the waterline, and far from the main water ingress points, to avoid the possibility of water being forced into the system during heavy swells.
• Use of Non-return Valves: A non-return valve or check valve may be installed in the vent pipe to prevent any backflow of sea water into the tanks.
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- How the Risk of Fire Entering the Ventilator Is Reduced (4 Marks)
To reduce the risk of fire entering the ventilator and potentially igniting the contents of the fuel or lubricating oil tanks, the following measures are typically implemented:
• Flame Arresters: Flame arresters are often installed in the ventilation pipes. These devices are designed to prevent any flame or spark from entering the tank by providing a physical barrier that extinguishes the flame before it can travel through the ventilation system.
• Spark-proof Ventilation Covers: Ventilators are fitted with spark-proof or fireproof covers to prevent external sparks or heat sources from igniting the flammable gases or vapors that may exit the tank through the vent.
• Ventilation Pipe Routing: The vent pipes are often routed in a way that directs the discharge of air and vapors away from potential sources of ignition, such as engine exhausts, machinery, or hot surfaces.
• Proper Maintenance of Ventilation System: Regular maintenance is carried out to ensure that there are no blockages in the ventilator system that could create conditions for an ignition source to be trapped inside the pipe. This also includes cleaning and checking for any foreign materials that could obstruct airflow.
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- How the Risk of Pollution Is Reduced (4 Marks)
The risk of pollution is reduced in the following ways:
• Water-tight or Oil-tight Seal at the Ventilator Opening: The ventilators are designed with seals that prevent any overflows of oil or water from leaking into the environment, particularly in the case of tank overfill or accidental spillage. This ensures that only air or gases are vented out and that pollutants do not leak from the tank.
• Oil/Water Separators: In many cases, vent systems are connected to oil/water separators or similar filtration systems that separate any oil or contaminants from water that might otherwise escape through the vent system. These separators ensure that oil is not discharged into the sea.
• Catchment or Drip Trays: Some ships install catchment trays or drip pans around the ventilators or tank openings. This prevents any accidental leakage of fuel or oil from the vent systems from dripping onto the weather deck or being washed into the sea.
• Compliance with MARPOL Regulations: The ship’s ventilation system must comply with MARPOL Annex I regulations regarding the prevention of oil pollution. This includes the use of suitable vent systems that minimize the risk of pollution, with regular inspections to ensure compliance with environmental standards.
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By following these preventive measures, the ship ensures the safety of both its fuel system and the surrounding environment, while maintaining operational efficiency and minimizing risk.q
Explain the meaning and purpose of EACH of the following ship terms:
a. Bilge keel; (4 marks)
b. Freeing port: (4 marks)
c. Longitudinal; (4 marks)
d. Frame. (4 marks)
- Bilge Keel (4 Marks)
Meaning: A bilge keel is a stabilizing appendage fitted to the sides of a ship, typically along the hull near the bilge (the widest part of the ship’s hull). It is a small, typically curved or fin-shaped protrusion that runs along the length of the hull.
Purpose:
• Reduce Rolling: The primary purpose of bilge keels is to reduce the rolling motion of the ship by providing resistance against the ship’s motion in the water. The keel helps to dampen the rolling caused by waves, making the vessel more stable in rough seas.
• Improve Stability: By adding hydrodynamic resistance, bilge keels also help in improving the overall stability of the ship, particularly during heavy weather conditions.
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- Freeing Port (4 Marks)
Meaning: A freeing port is a small opening or drain located on the side of a ship, typically near the deck, used to allow water to escape from the deck or the ship’s open spaces (such as cargo holds or weather decks).
Purpose:
• Water Drainage: Freeing ports are used to quickly release water that may accumulate on the deck during rough seas, heavy rainfall, or when the ship is rolling. This prevents the accumulation of water which can affect stability.
• Prevent Flooding: By allowing water to flow off the deck, freeing ports help maintain the stability of the vessel, ensuring that excessive water doesn’t enter the ship’s internal compartments, which could lead to flooding or loss of stability.
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- Longitudinal (4 Marks)
Meaning: “Longitudinal” refers to anything that is oriented or positioned along the length of the ship, running from the bow (front) to the stern (rear). It is often used to describe the structural members or frames of the ship that provide support along its length.
Purpose:
• Structural Integrity: Longitudinal strength members (such as longitudinal bulkheads or frames) help maintain the overall structural integrity of the ship by providing support along its length, helping the vessel resist stresses such as bending or twisting.
• Direction of Load: Longitudinal elements of a ship’s design are essential for handling the ship’s weight and the forces acting on it, such as waves, cargo, and machinery. These elements help in distributing loads along the length of the hull.
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- Frame (4 Marks)
Meaning: In shipbuilding, a frame refers to the structural members that form the skeleton or framework of the ship’s hull. Frames are typically spaced vertically and laterally along the length of the vessel to provide structural support to the hull and maintain its shape.
Purpose:
• Structural Support: Frames provide essential support to the outer shell or plating of the ship, helping the hull maintain its shape and integrity under stress.
• Basis for Hull Construction: Frames serve as the foundational structure on which the rest of the ship’s components, such as plating, bulkheads, and internal structures, are built. They are critical for the ship’s strength and durability, ensuring the ship can withstand external pressures like waves, cargo weight, and internal stresses.
Q9
Explain the meaning and purpose of EACH of the following ship terms:
(a) Keеl (4)
(b) Beam, (structural member) (4)
(c) Girder; (4)
(d) Frame. (4)
a) Keel
The Lowest structural member of a Ship which runs the length of the vessel at the Centerline and to which the frames are attached
Keel is the backbone of the Ship
(b) Beam (structural member)
A Transverse structural member supporting a deck and strengthening a Hull
The registered breadth of the Vessel measured at the outside of the hull amidships or at its greatest breadth
(c) Girder
Longitudinal continuous member with vertical web providing support of deck beams
Longitudinal continuous vertical plating on the bottom of single or double-bottomed vessels
(d) Frame
A steel plate that runs longitudinally or transversely throughout the hull structure
Frames are welded to the sides of the Hull
They are internal support member for the Shell plating
(a) Describe, with the aid of a sketch, a freeing port. (8)
(b) Explain how freeing-ports assist in maintaining the stability of a ship. (8)
a) A freeing port assists in maintaining the ship’s stability by allowing quick draining of the accumulated green (sea) water from the decks. Seawater can present a risk to stability if not drained promptly, as it can be of considerable weight and induce a free surface effect
(b) The freeing port maintains stability by quickly allowing large volumes of water to drain away which would otherwise be able to gather on the weather deck. The effect of this water would increase the mass of the vessel which would increase displacement and draft and improve gravity a little. Having this water collecting on the upper deck would raise the center of gravity, therefore decreasing GM, consequently, the righting lever GZ would decrease. This would adversely affect stability. The free surface effect could further decrease stability due to the large volume of water accumulating on the deck, which could cause a permanent list.
