Sanjeev Kumar - Marinerspoint Pro

Ballasting and deballasting of ship

June 30, 2021 by Sanjeev Kumar

Ballasting of ship is a process by which sea water is taken on ship in a dedicated ballast water tank while cargo is discharging.

Deballasting is a process by which sea water is carried out in sea from ballast tank when the ship loading cargo.

Simply,Ballasting or de ballasting is a process in which sea water is taken in and out from the ship for its stability when it at port or at the sea.

The sea water which is carried by a ship is called as ballast water.

What is the purpose of ballasting ?

The main purpose of ballasting a vessel for a voyage are to increase its manageability (and safety), especially in rough weather; control its draft and trim for maximum efficiency; and control its stability to ensure safe passage.

Must read :- Centrifugal pump

When ballasting or Deballasting required ?

It is required when the ship is
1.During Loading or unloading of cargo
2.to enter a channel
3.cross any canal like panama canal and Suez canal and
4 when ship is going for berthing.

Why sea water is used for ballasting ?

For ballasting vessel ,ballast water is sea water carried by a vessel in its ballast tanks to maintain the vessel’s trim, stability, and structural integrity. Ballast tanks on ships are outfitted with a piping system and high-capacity ballast pumps to carry out the operation.

As we know that for stability of ship, ballasting is done.In ancient time,Ship did the work of carrying hard weights/solid weights in form of rocks and sand bags for stability when there was minimum cargo or no cargo being carried.

However, as time passed, difficulties arose during the loading and unloading of solid cargo. Because the process of transferring solid cargo was time-consuming, solid ballast was replaced by water ballast. Because sea water was readily available in large quantities, it was used in the ballasting and de-ballasting processes.

Why is ballasting of ship done ?

Ballast water is carried on board vessels in order to maintain safe operating conditions during a specific voyage or portion of a voyage. Proper ballasting (in terms of the amount and distribution of water taken aboard) performs the following functions:

1.reduces stresses on the ship’s hull

2.ensures transverse stability

3.controls the propeller’s submergence, which aids propulsion.

4 improves maneuverability by submerging the rudder and reducing exposed hull surface (freeboard or windage)

5.compensates for the weight lost as a result of fuel and water consumption

Ballast condition, including when and how much water is loaded, determined by ship’s officees.It is determined on basis of the specific vessel’s operating needs and national and international requirements for proper vessel trim and stability at sea.

Ballast conditions at sea

Heavy weather conditions

Ships must be anchored deep enough in the water to ensure safe passage, especially in bad weather. If the bow of the ship is not deep enough, the ship’s forefoot will emerge from the water surface on a regular basis. This causes hull slamming (or heavy impact) when the bow hits the water with high velocity on re-entry.

Sailing with full tanks

Depending on the ship’s stability and strength requirements, ballast tanks used to control trim or heel, some fuel oil tanks, and tanks containing fresh water for domestic use may be partially full at sea. It is usually necessary to sail with as many of the tanks on board as possible, either completely full or completely empty. When a tank is not completely full (i.e., “slack”) and the ship heels, the free surface effect of the liquid in the tank moves the center of gravity of the liquid in the tank, reducing the ship’s transverse stability (see Appendix C).

Furthermore, fluid in a slack tank sloshes around during ship motion, which cause excessive loads on tank/hold bulkheads, frames, or underdeck structure. This could lead to structural failure in severe weather conditions. As a result, when changing ballast at sea, the ballast in a single tank or pair of tanks should be completely changed before moving on to the next tank or tanks.

Controlling trim during voyage

The draft and trim of the ship will change as fuel is consumed during a voyage. Thousands of tons of fuel may be consumed during a long voyage. As a result, in order to keep the hull immersed correctly for maximum efficiency, additional ballast is frequently required as the voyage progresses. Some ship designs position the fuel tanks so that the ship naturally trims by the stern as the fuel oil is consumed, but ballasting may still be necessary. Ballast capacity and location on a given voyage are determined by examining the estimated amount of fuel to be consumed, the expected weather conditions, and the required draft and trim for the arrival port (s).

Transverse stability considerations

A ship’s transverse stability is defined as its ability to sail upright and avoid capsizing. To achieve proper transverse stability, the ship’s righting moment must be carefully controlled (see Appendix C). The ship should ideally be loaded and/or ballasted in such a way that it has a smooth rolling period that is neither too fast nor too slow. A ship that rolls too fast has excessive stability (a stiff ship) and has a strong tendency to quickly return to its original upright position. This causes a very uncomfortable motion that can put a lot of strain on the ship’s structure and cargo lashings, as well as a lot of sloshing in the slack tanks.

A vessel that rolls too slowly has insufficient stability (it is a tender ship) and may capsize in bad weather. When ballast is moved, it causes slack ballast tanks to form. When the vessel heels, the associated free surface effect can cause a weight shift, which has a negative impact on the ship’s transverse stability.

Ballast conditions in port

Bulk oil carriers (tankers), dry bulk carriers, and the majority of other ships deballast during cargo loading and reballast during cargo discharge (see Table 2-1). A fleet of ships operates as float-on, float-off platforms, with the ship ballasted down to allow cargo to be floated on board and deballasted to lift the cargo for the journey. For unloading, the procedure is reversed.

Controlling draft and trim for port entry

Vessel must alter draft and trim to when entering to ports ,Berths,or both at loading or unloading.
Ballast may be discharged to reduce water drafts when entering certain ports or approaching specific terminals, and it may be added to reduce air draft when clearing bridges or approaching under loading heads at some bulk cargo terminals. These operational parameters can limit the timing and location of ballasting and deballasting.

Safe longitudinal loading consideration

The distribution along the hull of the difference between the light ship weight, including cargo, fuel, ballast, and other dead weight items, and the supporting buoyancy force determines the shear forces and bending moment on a ship’s hull. Buoyancy support forces change in a seaway as waves move along the hull and the hull moves relative to the sea surface. The ship operator must ensure that the ship’s in-service conditions are consistent with the ship’s structural design.

Summary of Ballasting or Deballasting

When the ship is not carrying cargo, it becomes light in weight, which can affect its stability. As a result, ballast water is stored in dedicated tanks on board the ship to stabilize it. Ballasting is the process of filling tanks with ballast water using large capacity ballast pumps.

When the ship is loaded with cargo, the weight of the cargo itself maintains the ship’s stability, and thus no ballast water is required. De-ballasting is the process of removing ballast water from ballast tanks in order to empty them.

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Source :- https://en.m.wikipedia.org/wiki/Ballast

Fuel Oil System in Ship For Marine Diesel Engine

September 28, 2024June 25, 2021 by Sanjeev Kumar

Fuel oil system in ship For marine diesel engine are which operate on heavy fuel oils: Fuel oil transfer system, Fuel oil treatment system and Fuel oil supply system.Various piping systems for bunkering, storage, transfer, offloading, and treatment of fuel oils are provided.

Fuel Oil Transfer System

This system receives, stores, and delivers fuel to settling tanks. Fuel oils are loaded through deck fill ( bunker manifold ) connections with sample connections to allow the fuel to be sampled as it is brought aboard. HFO is stored in tanks equipped with heating coils.

HFO is transferred to the fuel oil settling tanks via FO transfer pumps equipped with a suction strainer in preparation for use. The piping is set up so that the pumps can transfer fuel from storage tanks to deck connections for offloading. Settling tanks are used to allow gross water and solids to settle to the bottom of the tank.

Fuel Oil Treatment System

Fuel oil is transferred from the settling tanks to the service tanks via the FO treatment system. The two-stage process is commonly used for cleaning heavy fuel oils (HFO). The fuel is heated to about 50-60°C in a settling tank before being drawn out by the purifier inlet pump.

The fuel is delivered by the inlet pump to a thermostatically controlled heater, which raises the fuel temperature to approximately 80°C, and then to the centrifugal purifier. The purifier discharge pump then transfers the dry purified fuel to a centrifugal clarifier. Following clarification, the clarifier discharge pump transports the fuel to the service tank for use by the engine.

Fuel Oil Supply System

The fuel from the service tank is delivered to the diesel engine via this system.
This system consist of :-
1.Fuel oil storage tank (heavy fuel oil )
2.Transfer pump
3.settling tank
4.Circulating pump on separator
5.Preheater
6.Seperator
7.Tank for purified oil
8.Shut off valves
9.Tank for purified diesel oil
10.Shut off valve
11.3-way valve
12.Flow meter
13.Mixing tank
14.Vapour trap
15.Booster pump
16.preheater
17.Filter, heatable
18.Thermometer
19.Fuel pump feed pipe
20.Fuel injection pump
21.High – pressure fuel pipe
22.Fuel injector
23.Diesel Engine
24.Fuel return pipe
25.Pressure Gaye
26.Constant Pressure Valve
27.Prewarming by -pass

Fuel oil supply for a two-stroke diesel engine

A slow-speed two-stroke diesel engine is usually configured to run continuously on heavy fuel and to have a diesel oil supply available for maneuvering purposes.

The oil in the system shown in Figure is stored in tanks with a double bottom, from which it is pumped to a settling tank and heated. After passing through centrifuges, the cleaned, heated oil is pumped to a daily service tank.

To ensure constant supply of fuel to the mixing tank via the fuel oil pipes and the flowmeter,the heavy fuel oil tank should be located high enough over the mixing tank.To rule out the possibility of heavy fuel oil entering the diesel oil day tank ,the latter should be located above the heavy fuel oil tank or protected by means of a non return valve.

The oil flows from the daily service tank to a mixing tank via a three-way valve. A flow meter is installed in the system to monitor fuel consumption. Booster pumps are used to deliver oil to engine-driven fuel pumps after passing it through heaters and a viscosity regulator. The fuel pumps will deliver high-pressure fuel to the injectors.

The viscosity regulator regulates the temperature of the fuel oil in order to provide the proper viscosity for combustion. A pressure regulating valve ensures that the engine-driven pumps have a constant supply of pressure, and a pre-warming bypass is used to warm up the fuel before starting the engine.

A diesel oil daily service tank that is connected to the system via a three-way valve can be installed. The engine can be started and maneuvered using diesel oil or a combination of diesel and heavy fuel oil. The mixing tank collects recirculated oil and also serves as a buffer or reserve tank, supplying fuel when the daily service tank is empty.

In the event of problems during manoeuvring on heavy oil engines, there should be no hesitation in switching to diesel oil, regardless of whether the engines are operated via bridge control or engine room control.

Main engines designed to run on heavy fuel oil must be used in accordance with the manufacturer’s instructions. All other types of main engines must be operated on diesel oil in accordance with the manufacturer’s instructions.

Safety services fitted on fuel system on ship

The system includes several safety devices, including low-level alarms and remotely operated tank outlet valves that can be closed in the event of a fire

1.Quick closing valves on settling/service tanks
2.relief valves on 2 pumps/heaters
3.quick closing valve on mixing/vent tank
4.pipes lagged/save-alls under pumps and heaters
5.low fuel oil pressure alarm
6.high fuel oil pressure alarm
7.low fuel oil temperature alarm
8.high fuel oil temperature alarm
9.emergency remote stops for pumps
10.high pressure pipes between fuel injection pump and injector are double skinned.

Of Each Components of fuel oil system of ship

1.Service tank :-Fuel is transferred to the service rank via a centrifuge from service tank.

2.Change over switch :- The switch in the engine control room or the handwheel on top of the valve can be used to operate the change over valve automatically.

It used to be common practice to switch to diesel fuel for maneuvering purposes. Modern methods of fuel oil recirculation to keep the fuel hot at the injectors have rendered this practice obsolete.

3.Quick closing valve :- Fuel is drawn from service tank through a quick closing valve. These can be closed remotely in case of emergency (e.g. fire). This can be done with simple pull wires, hydraulically, or by compressed air.

The fuel then passes via the change over valve through a set of filters into the supply pumps.

4.Filter :-A suction filter removes any particles that could cause damage before the fuel enters the supply pumps. There are two filters, one for each of the two pumps. They are made of fine metal gauze and can be cleaned and reused as needed.

5.Pump :- The pressure is raised to about 7 bar by the supply pumps. A pressure regulating valve is used to keep the discharge pressure constant.

6.Regulating valve :-There is also a manual bypass which can be used should the regulating valve develop a fault.

7.Auto back filter :-The fuel is passed from the supply pumps to a series of backflushing filters (25 micron). The filter elements are housed in the pods. When the filters begin to clog, a differential pressure sensor triggers a backflushing routine, which allows the filters to clean themselves. Backflushing oil containing sediment from the filters drains to the fuel oil drain tank, where it can be recovered and purified.

When a mesh type filter is used, the filter can be removed from service line for cleaning.

8.Flowmeter :-

The fuel is pumped via a meter so that the quantity of fuel used can be monitored and the specific fuel consumption of the engine calculated.

In the case that the meter has to be bypassed, then the fuel is led across a pressure retaining valve.

9.Mixing column :- The fuel is then passes to a mixing column or buffer tank where it mixes with returned fuel from the main engine.

The mixing column is fitted with a relief valve and an air release (see in the fig ) and the outlets from these are led via a sight glass to the fuel oil drain tank.

10.Booster pump :- Fuel oil circulating pumps from the buffer tank pressurize the fuel to about 8 bar before it is passed to the heaters and engine.

11.Steam is used to heat the oil (although thermal oil or electric heaters are used on other systems). A viscosity measuring device regulates the temperature of the oil. The viscosity must be kept at the proper level for injection. It is set to 16 centistokes on this particular system.

12.Filter :-
After passing through the heater and before reaching the main engine inlet rail, the fuel is filtered once more to ensure that it is free of abrasive contaminants that could damage the fuel pumps, injectors, and cylinder liner.

13.Fuel oil inlet rail :-

Fuel enters each fuel pump from the main engine inlet rail (one per cylinder). The fuel pump delivers high-pressure fuel (250bar or higher) to the fuel injector (s).

14.The fuel return is the lower connection on the fuel pump. More fuel than is required is delivered to the pump. The surplus is returned to the buffer (mixing) tank.

The atomized fuel is delivered to the cylinder by the fuel injectors. When no fuel is being injected, the injectors recirculate back to the fuel return.

14.Back pressure control valve :- A backpressure control valve is installed on the return line to keep the fuel oil pressure at the required level (on this system, about 8 bar).

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Refrigeration Cycle – Know All the Stages, Components & Diagrams

August 17, 2025June 22, 2021 by Sanjeev Kumar

In this article, I am going to explain about refrigeration cycle in details like definition of Refrigeration, What are the 4 cycles of the refrigeration system? What is the principle of refrigeration? What are the parts of refrigerator? Refrigeration cycle diagram and working. Before starting first understand the term refrigeration.

What is Refrigeration ?

Refrigeration means cooling a space, substance or system to lower and/or maintain its temperature below the ambient one (while the removed heat is rejected at a higher temperature). In other words, refrigeration is artificial (human-made) cooling.

What is Refrigeration Cycle ?

Refrigeration cycle is a cycle of mechanical system in which transmission of heat flow from one place at a lower temperature (the source ) to another place at a higher temperature ( the sink or heat sink ) by continuously circulating, evaporating, and condensing a fixed supply of refrigerant in a closed system.

Refrigeration cycle is a thermodynamic cycle to generate refrigerating effect with the use of evaporator, compressor, condenser & expansion valve.

Refrigeration cycle name – It is also called heat pump cycle .

Thus, a heat pump is called as a “heater” if the objective is to warm the heat sink (as when warming the inside of a home on a cold day), or a “refrigerator” or “cooler” if the objective is to cool the heat source (as in the normal operation of a freezer).

In both cases, the working principles are same. Heat is removed from a cold place to a warm place. Below given is the refrigeration cycle diagram :

Refrigeration Cycle Diagram

Refrigeration Cycle working principle Diagram

Vapour Compression Cycle

Vapour Compression Refrigeration system is the most widely used refrigeration system.

Vapour compression refrigeration cycle is a process that uses the physics of phase change heat transfer and the unique properties of a refrigerant to transfer heat from a relatively cold source to a hot medium.

What is the Basic Refrigeration Cycle ?

The basic components of any refrigeration system working on the vapour compression cycle are the compressor, condenser, expansion valve and evaporator and the refrigerant fluid which is alternatively vaporized and liquefied during the refrigeration cycle.

The temperature at which a fluid boils or condenses is known as the saturation temperature .

Components of Refrigeration Cycle

The 4 main Components of Refrigeration cycle

1. Compressor
2. Condenser
3. Expansion valve
4. Evaporator

Refrigeration Cycle Working

Working of vapour compression refrigeration system has been explained step by step including the work done by each component in the cycle and can be seen in the refrigeration cycle diagram also.

1. Compressor

The compressor in a vapor compression cycle helps in raising the pressure of the vaporizer refrigerant, causing its saturation temperature to rise, so that it is higher than that of the the sea water or air, cooling the condenser. The compressor also promotes circulation of refrigerant by pumping it around the system.

Note :- Refrigerant enters the compressor as low-pressure, low-temperature gas, and leaves the compressor as a high-pressure, high-temperature gas.

Why compression takes place :- Compression takes place to raise the saturation temperature and refrigerant pressure.

2. Condenser

In the condenser of the vapour compression system the refrigerant is liquefied by being subcooled to below the saturation temperature relating to the compressor delivery pressure, by the circulating sea water or air for domestic refrigerator.

Latent heat, originally from the evaporator, is then transferred to the cooling medium. The liquid refrigerant, still at the pressure produced by the compressor, passes to the receiver and then to the expansion valve.

Note :- After condensing, the refrigerant is a high-pressure, low-temperature liquid, at the point it’s routed to the loop’s expansion device.

What happens in condenser :- Heat is transferred from the refrigerant to a flow of water

3. Expansion valve

The expansion valve is the regulator through which the refrigerant flow from the high pressure side of the system to the low pressure side. Its throttling effect dictates the compressor delivery pressure which must be sufficient to give the refrigerant a saturation temperature which is higher than the temperature of the cooling medium.

The pressure drop through the regulator causes the saturation temperature of the refrigerant to fall so that it boils at low temperature of the evaporator. In fact, as the liquid passes through the expansion valve, the pressure drop makes its saturation temperature fall below its actual temperature.

Some of the liquid boils off at the expansion valve taking latent heat from the remainder and causing it’s temperature to drop.

The expansion valve throttles the liquid refrigerant and maintains the pressure difference between the condenser and evaporator, while supplying refrigerant to the evaporator at the correct rate. It is thermostatically controlled in modern systems.

What happens to refrigerant in Expansion valve :- When the refrigerant enters the throttling valve, it expands and releases pressure. Consequently, the temperature drops at this stage.

4. Evaporator

The refrigerant entering the evaporator coil at a temperature lower than that of the surrounding. Secondary coolant (air or brine ) receives latent heat and evaporates. Later the heat is given off in the condenser, where the refrigerant is again compressed and liquefied.

Note :- Refrigerant enters the evaporator as a low temperature liquid at low pressure, and a fan forces air across the evaporator’s fins, cooling the air by absorbing the heat from the spaces.

What happens to refrigerant in evaporator :- It evaporates and absorbs latent heat of vaporization.

For a small refrigerator the evaporator cools without forced circulation of secondary coolant. In larger installation, the evaporator cools air or brine which are circulated as secondary refrigerants.

Frequently Asked Questions

What is the refrigeration cycle called?

Refrigeration cycle is also called heat pump cycle

What are the 4 cycles to the refrigeration system?

The 4 main Components of Refrigeration cycle are :
1. Compressor
2. Condenser
3. Expansion valve
4. Evaporator

What Are the Different Types of Refrigeration Systems?

There are four main refrigeration cycle types :
1. Mechanical Compression Refrigeration System
2. Absorption Refrigeration
3. Evaporative Cooling
4. Thermoelectric Refrigeration

Which gas is used in refrigerator?

Tetrafluoroethane:

HFC-134a (1,1,1,2-Tetrafluoroethane) is one of the commonly used refrigerant gases which you can find in almost all the present time refrigerators.

we have covered all the required details of Refrigeration cycle ( vapour compression refrigeration system, vapour compression cycle, heat pump cycles ). This is the most basic refrigeration cycle and is known by many different names as mentioned. We got refrigeration cycle explained with the help of refrigeration cycle diagram and learned the thermodynamics of refrigeration.

For Better Explanation

Refrigeration Cycle Explained on YouTube

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Piston cooling in 2 stroke marine Diesel Engine

September 28, 2024June 17, 2021 by Sanjeev Kumar

In this article I am going to explain piston cooling in 2 stroke marine diesel in details.

Cooling of piston is done to to prevent stresses in the piston crown due to temperatures induced by combustion.

Piston cooling in 2 stroke marine diesel engine (The maine engine piston cooling ) is done by one of the cooling medium –

1. Water and

2.oil

Note :- Water-cooled pistons were mainly used in old MAN engines and Sulzer RND ,RLA and RLB engines.

Nowadays both MAN B & W and Sulzer engines prefer oil cooling to conventional water cooling piston.

Why Oil Cooling is preferred to conventional water cooling piston ?

Ans :- as the former reduces the risk of lube oil contamination in case of leakage.

Difference in piston cooling of sulzer and B & W Engines

In Wartsila engine , an articulated or swinging arm is attached to the crosshead which supplies the inlet oil.

In B&W Engines Telescopic pipe is used for supplying oil to the crosshead which supplies oil to the inlet pipe of piston rod.

MAN B & W

A branch of lube oil goes to crosshead.In MAN engine the lube oil is connected to inlet in the crosshead using a telescopic pipe,it moves up and down along with the crosshead and oil is supplied to it from the top .

Figure showing oil from telescopic pipe branching for piston cooling

Animations of crosshead and telescopic pipe

Once the oil reaches the engine inlet it does three functions

A.Some oil travel up the piston rod to cool the piston and then comes down.

B.Some oil lubricates the crosshead bearing and the shoe guides.

C.the remaining oil passes through a hole drilled in the connecting rod to the bottom end bearings.

And finally all oil comes to the sump.

How oil branching taking place

For understanding, How oil passes through piston rod to piston see the below figure :-

There is 3 hole showing in bottom of piston rod ( This bottom will sit on crosshead ) for flow of oil.One is in centre and other 2 is in the side.

Actually,The piston rod is utilised to carry the oil to and from the piston.The rod is hollow, and has a tube running up its centre. This gives an annular space which, with the central bore, allows a supply and return.

Flow pattern of oil

The cooling oil is delivered to the piston crown, through the centre of the hollow piston rod, circulating through the cooling channels in the crown. The oil returns through the piston rod via small holes drilled into the piston rod where it is collected in a tray at the cross head bearing. here the oil temperature and viscosity is monitored before spilling over the tray; cascading down into the main lube-oil sump.

MAN B&W Piston:

The new MAN engine uses simple bore cooling piston and jet nozzels, which comprises of oil passage within the piston crown for uniform cooling. The MAN engine also uses a top layer thermal coating over the crown, known as INCONEL 625 coat, which is 8mm thick and protects the crown surface from overheating.

Sulzer Engine

The oil in sulzer engine provided through articulate pipe.Two pipe is provided in articulate pipe.

One pipe go for crosshead lubrication (and after xhead it goes for bottom end bearing lubrication ) and second pipe for piston cooling.

Actually,The rod is hollow, and has a tube running up its centre. This gives an annular space which, with the central bore, allows a supply and return.

There is 3 hole showing in bottom of piston rod ( This bottom will sit on crosshead ) for flow of oil.One is in centre for return oil and other 2 is in the side for cooling piston.

Flow pattern of oil coolant

The Cooling oil Is delivered to the piston crown in sulzer engine is through the two outside holes in the piston rod.The larger bore being used for return oil after cooling.

This allows oil delivery at a higher pressure to the nozzles; causing it be injected as a mist against the inside surfaces of the crown and providing a more efficient cooling system.

SULZER Piston:

The new SULZER piston with concave crown comes with Jet-Shaker cooling design, wherein the jet nozzles are attached to the cooling passage of piston rod.

The piston crown design which comprises of bores and nozzles ( for supplying cooling oil with high pressure), provides better uniform cooling and reduces crown thickness and overall piston weight. This is known as jet shaker method as during downward movement of piston, the nozzle sprays the oil jet inside the bore and when the piston moves upward, the oil inside the piston crown shakes for efficient cooling.

Water Cooled Piston of Marine Diesel Engine

The diagrammatic sketch shows the general arangement for the main engine piston cooling
water system for Sulzer RD type engines.

Note:-This is line diagram of sulzer RD types engine in which one figure cooler is between sight glass and tank and in other figure cooler is after pump.I have also seen cooler is after pump in sulzer RLA and RLB engines.

The piston cooling water tank is located at lower level to allow the return cooling water to flow easily into the tank. A piston cooling pump draws the water from the tank and pumps it through the cooler into the piston through telescopic pipe arrangement.

The cooling water returns via a second telescopic pipe to the tank. Each return line has a thermometer, a flow sensor with ‘no flow’ alarm and a sight glass to observe the flow of water.

A connection is provided in the piston cooling tank as shown for the replenishment of water
as and when necessary.

A centrifugal pump supplies the cooling water under pressure to the piston crown; where it is circulated through water channels that have been cast into the piston crown.

These channels are positioned close to the walls and top of the crown, also behind the piston ring grooves to promote optimum cooling of the surfaces of the crown subjected to the high temperatures of combustion.

The water enters and leaves the piston through telescopic pipes that slide up and down on stand pipes as the piston reciprocates. These pipes have rubber water seals between them to prevent leakage of cooling medium into the crankcase lube-oil. There can also be enclosures around the seals that incorporate tell-tale leak pipes that eject water if a seal begins to leak. The pipes are located at convenient locations outside the engine enclosure, usually at control platform level.

The water temperature is maintained by a dedicated seawater cooler, and a header tank allows the system water and additive to be topped up.

Advancement of piston chamber

In water cooled piston,ribs is removed and made a bore inside which provide jet cooling.

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Bulwark on a Ship: Definition, Height, Constructions

September 28, 2024September 24, 2020 by Sanjeev Kumar

Bulwark on a Ship

What is a Bulwark on a Ship ? Bulwark Definition

Bulwark on a ship is a nautical term for a ship’s side to be extended above the level of a weather deck.

Define Bulwark

It is a Vertical Fore-and-aft plating just above the upper edge of the side of the ship surrounding the exposed deck(s).

Bulwark ship meaning : It is defined as boundary designed on the ship’s side to prevent passengers and crew from falling to sea.

As protection for crew and passengers, bulwarks fitted on weather decks and it is not intended as a major structural function.

Bulwark Definition : In simple sentence, bulwark meaning , a solid wall like structure fitted on the ship’s side above the upper deck to protect crew member falling into the sea.

As we know that it is fitted only to save falling crew and not intended as major structure so, they are of light scantling. The high stresses connected to adjacent structure is avoided.

Also read :- Difference between 2 stroke and 4 stroke engine

Freeing ports

Freeing ports are the opening provided on the ship side to allow the free passing of water on the deck to the sea freely.

Or,

It is an Opening or hole in the bulwarks at the level of the deck to drain water from the deck.

As we see the figure of Bulwark ,it is open.

Why it is open ?

The opening is called freeing ports.

Freeing ports are cut into bulwarks forming wells on decks so that the water can drain quickly.

Freeing ports area on each side depend on the length of well deck.

The ports’ lower edge must be as close to the deck as possible. It is appropriate to fit bars spaced about 230 mm apart across the port. Where hinge flaps are fitted and these hinges should be non-corrodible.

Structure of the Bulwark on a ship

What is the height of Bulwark ?

The height of Bulwark is at least 1 metre high on the exposed freeboard and the superstructure deck.

However, a reduced height may be allowed if this interferes with the operation of the ship.

Range of height

In open position,the height should be 1 metre high.These are supported by stanchions.

In some ships,these must not be more than 1.2 metres apart for forward 7 percent (%) of the length of the ships otherwise,it not be more than 1.83 metres.

Construction of the Bulwark on a ship

Bulwark should not be welded to the sheer strake to the half length amidship as this is liable to cause the plating to crack.

This can be done by riveting the bulwark to the sheer strake or by using FLOATING BULWARK, which has the advantages that the space/gap between it and the edge of the deck serve as a freeing port.

It is normally founded in a rounded sheer strake.

More photos

So with this article we understand bulwark meaning along with more than one bulwark definition. Bulwark on a ship is very important from safety point of view.

What is camber of a ship?

In naval architecture, camber is a measure of lateral main deck curvature. The curve is applied transversely to a deck and is measured as the height of the deck at the centerline above the height of the deck at the side.

What is a girder on a ship?

A girder is a longitudinal member used in the construction of a ship’s bottom. They can be solid or hollow, and they can be placed above the keel (centre girder) or equally spaced from it (side girders). They can be continuous or divided into sections by floor sections (intercostal side girders).

What is ship gangway?

A gangway is a narrow walkway or platform that allows people to safely board a ship, truck, or train. Gangways are typically used for two purposes: allowing people and/or cargo to travel to and from docks, moored marine vessels, or aircraft, or for maintenance and loading/unloading of land-based trucks and trains.

What is the function of bulwark?

It is defined as boundary designed on the ship’s side to prevent passengers and crew from falling to sea. As protection for crew and passengers, bulwarks fitted on weather decks and it is not intended as a major structural function.

Where is bulwark located?

The Bulwark, located on the border of Tirisfal Glades and the Western Plaguelands, is the Forsaken’s last line of defence against the forces of the Scourge to the east.

What is ship keel?

The main structural member and backbone of a ship or boat, running longitudinally along the bottom of the hull from stem to stern in shipbuilding. It could be made of wood, metal, or another strong and stiff material.

What is camber and sheer?

Camber:-The deck’s transverse curvature from the centerline to the sides. This camber is used on exposed decks to direct water to the ship’s sides.
Sheer: The fore and aft curvature of the deck, rising from midship to the maximum at the ends.

What is strake in ship?

A strake is a longitudinal course of planking or plating on a vessel’s hull that runs from the boat’s stempost (at the bows) to the sternpost or transom (at the rear). The garboard strakes are the two on each side immediately adjacent to the keel.

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Windlass safety devices

May 28, 2020 by Sanjeev Kumar

What are windlass Safety Devices ?

Windlass Safety devices are :-

Overload trip
Emergency stop
Mechanical break
Over speed trip
Slipping clutch for overload,for preventing any undesirable damage such as hull damage due to anchor and rope brake out.

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Why discharge valve closed during starting of centrifugal pump ?

August 17, 2025May 24, 2020 by Sanjeev Kumar

In this Article, I have Explained Why discharge valve closed during starting of centrifugal pump ? Or Why centrifugal pump started with closed discharge valve ?

Why centrifugal pump started with closed discharge valve ?

Let Us First Understand through Characteristics Curve of Centrifugal Pump. A centrifugal pumps usually started with discharge valves shut.

Considering the properties of centrifugal pump by operating characteristic curve it is clearly found that; when the amount of water delivered is zero, the power available is at minimum.

So discharge valves valve remains shut off throughout the beginning to take care of low power demand by the pump on its motor having low power output at the beginning.

This helps stabilizing pumps at the starting. When the pump is stable the discharge valves opened and high power avaibility meets the high power demand; which might be not possible for the motor to fulfill for the starting 4-5 seconds.

Why discharge valve closed during starting of centrifugal pump ?

Or,

It is a very common practice to start large capacity centrifugal pump with the closed discharge valve .

If the characteristic curve for a centrifugal pump are examined it will be seen that when the quantity of water discharged is zero the power required by the pump is zero or very small amount.

by starting the pump with discharge valve closed the power demand made by the pump on the pump motor is kept to very minimum after the pump has started and the momentary high motor current demand has stabilized the discharge valve is opened.

Why centrifugal pump started with closed Discharge valve

By closing the discharge valve, the starting current can be reduced.

As we know, at the start of any motor, the current will be high. When we start the pump with an open discharge valve, the discharge head will act on the pump, i.e. more resistance, so that the motor has to give more starting torque to the pump, which means more current is drawn by the motor.

If we start the pump with discharge valve closed, it means there no discharge head and minimum resistance to the pump and so current drawn is minimum. Although the current taken during startup of motor is more than normal, but by closing the discharge valve of centrifugal pump we can avoid extra load act on the pump.

If there is a check valve, then the discharge valve can be opened. Without having a check valve, we need to have the discharge valve closed if there is pressure on the discharge side of centrifugal pump at the time of startup.

If we think differently,If there is a pressure on the pump’s discharge side,before starting it may flow back through the pump,causing a backward spin and can draw more current , resulting damage to the pump.Thus can be prevented by keeping the discharge valve of centrifugal pump closed when starting.

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What is difference between hyper mist and sprinkler system?

May 20, 2020 by Sanjeev Kumar

What is difference between hyper mist and sprinkler system?

Hyper mist :-

It use fresh water
It activate when two different detectors activated.
Pressure required for hyper mist is more as compare to sprinkler system.
Droplet size of hyper mist is small

Sprinkler System :-

It uses Sea water
Sprinkler has Temperature bulb
Pressure Required for sprinkler system is less as compare to hyper mist.
Droplet size of sprinkler system is bigger than hyper mist.

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What is Angle of Contraflexure?

May 20, 2020 by Sanjeev Kumar

In this Article,we will learn What is the Angle of Contraflexure ?

What is angle of Contraflexure ?

This is the angle at which the curve goes / moves from concave to convex.

It is the angle of heel up to which the rate of righting lever ( GZ ) With the heel is changes I.e Before this point rate of righting lever with heel is increasing but after this point rate of righting lever will decrease.

Must Read:- How does a ship move

What is it’s significance ?

The physical Significance of this point is that ,it is the point or angle at which Deck just touches the surface of sea.

The below figure is the Curve of Statical stability for a ship in Particular condition of loading.

How this Curve Obtained ?

This curve is obtained by plotting the Righting Lever against the angle of the heel.

The above curve is for Positive Metacentric Height

The above curve is for negative Metacentric Height.

From the above figure we can get following information:-

Range of Stability :-The range in which the ship has positive Righting lever (GZ ) i.e 0 – 86 in figure 3. & 18- 9 in figure 4.
Angle of vanishing stability:-It is the angle of heel when the righting lever (GZ ) returns to zero,or the angle at which the sign of righting lever changes from positive to Negative I.e 86 degree in the figure 3.
Maximum GZ :-It is obtained by plotting a tangent to the highest point of the Curve. i.e 0.63 meters which occurs at 42 degree.
Initial GM :-It is found by Drawing a tangent to the curve through the origin and then erecting a perpendicular through the angle of her log 57.3 degree.The two lines are allowed to intersect and the value of GZ is noted which is initial GM.
Point of Inflection/Contraflexture :-It is the angle at which the curve goes / moves from concave to convex.

The above figure is for Negative Metacentric Height.

In the above figure,we can see that ,at an angle less than 18° the the righting arm / lever are negative and beyond 18° to 90° the righting lever is positive.

Hence, 18 degree is the angle of look or point of loll.

Note :- Initial GM of ship is plotted at 57.3°.

Now the Question come in mind that why we take Initial GM of ship at 57.3° ?

The answer of this Question is that 57.3 °= 180÷ 3.14 57.3°.

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Ship stability wikipedia

Clarifier || Purifier || How to convert Purifier into Clarifier

May 18, 2020 by Sanjeev Kumar

In this Article ,I have mentioned How to convert purifier into clarifier ?

Beside it,you will also learn listed topic in this Article.

Difference Between Purifier and clarifier
Why Clarifier not converted into purifier
What is Blind Disc
What is sealing water line
What is gravity disc ?

Changing purifier into clarifier

Open the purifier and place the blind disk at the bottom of the disc stack.
The water outlet is blocked by a seal on the gravity disc.
Blank off the inlet line of sealing water.

For better understanding watch video:-
https://youtu.be/bdCiOitnjGA

Must read:- Purifier

Can Clarifier change into purifier

Answer is NoIt is because in clarifier there is no water outlet and sealing water line.

Difference between Puri fier and Clarifier

Purifier

There is holes in the upper disc .
It Separates water and solid particles.
It has two Outlet on top, a)Water outlet and b )pure oil outlet.
There is a Gravity disc on top of disk stack.
For starting of purifier ,Sealing Water required.
Top disk with neck

Clarifier

There is no holes in the lower disc.
It Separates only solid particles.
There is No Gravity disc
Only cleaned Oil Outlet at the top
Sealing water does not required
There is Disk without neck

What is blind disc in the purifier ? What is it’s function ?

Blind Disc means the disc is blind.It means there is no holes in the disc.It is used to convert the purifier into clarify. It is inserted at the bottom of the disk stack, because there are no holes.

What is Gravity Disc ?

A ring fitted at the top of disc stack from where water is passing out is called gravity disc.Oil maybe of different densities,so the interface changes.To create the correct line of interface between water and oil it is very important to select correct gravity disc size.

The function of gravity disc are as follows

gravity disc in the purifier is one which controls the output of the quantity of fuel. It is responsible for creating the interface between the oil and water.
Back pressure is maintained by gravity disc.

It is responsible for creating the interface between the oil and water.
Back pressure is maintained by gravity disc.

What is sealing water line?

In a purifier, water sealing is established before introduction of the oil, so that oil filling does not flow through the heavy liquid outlet.

Purpose :-
To seal the water outlet & also to prevent the overflow of oil through the water outlet.

For better understanding ,How purifier change into clarifier and why not clarifier change into purifier, please read full Article .

I am 100 percent sure,After reading this 5 minute article you have no Doubt.

Basic Principle of separation

Basic principle of separation of water and impurities from fuel is gravity difference.

Separation as a means of removing impurities from a fuel can be carried out by gravity in a settling tank or by centrifugation of the fuel.

Both methods work on the same principles that, by subjecting the constant force to fuel, the denser components of the fuel, i.e. water and soil, will be separated from the lighter components , i.e. the fuel itself.

The gravity acting on the fuel as it passes through the tank slowly separates the denser components from the fuel where they accumulate at the bottom of the tank. The contaminants can then be removed by sludging the tank.

Centrifuging

Centrifuging is a process by which the gravity effect can be amplified by the use of centrifugal force to the extent that the separation process becomes rapid and continuous. Centrifuges operate, rapidly by spinning a bowl containing the liquid, thus producing the centrifugal force required for separation.
Its principle of operation of is very simple.

When a bowl containing impure fuel is rotated, the centrifugal forces throw any item with a density greater than the density of fuel oil (solids and free water) to the bowl ‘s periphery.

Centrifugal separators used to separate two liquids with different densities (fuel and water) are known as purifiers, and clarifiers are those used to remove solid impurities.

Note:- Purifiers will also remove some solids, and clarifiers will remove small amounts of water as well.

Clarifier

In above figure,the addition of an inlet and an outlet connection forms a simple clarifier.

Rotational speeds vary by design and range from 7,000 to 9,000 rpm. Efficiency is increased by the inclusion of a number of dicks (up to 150) which increase the surface area and thus help in separation of impurities from fuel. The dicks are placed at a distance of 0.5-0.6 mm.
After passing through the central passage, the untreated oil is moved by centrifugal forces to the periphery of the bowl and then passes through the disk stack. Here is where the actual separation takes place, in a channel formed between two disks. Two forces are acting on each solid or liquid particle.

The particle is pushed upwards by the oil stream to the centre, while the centrifugal force directs it to the periphery.

The residual force on the denser particles (impurities) will drive them towards the periphery, while the less dense particles (oil) will be directed towards the center of the bowl and will rise to the outlet connection.

Purifier

When a centrifuge is configured as a purifier, the second outlet pipe is used for the discharge of water as shown in figure.

In the fuel oil purifier, the untreated fuel contains a mixture of oil, solids and water, which is separated into three layers by the centrifuge.

While in operation, a quantity of oil remains in the bowl to form a complete seal around the underside of the top disk and, due to the difference in density, the oil is confined to the outer diameter of the top disk.

Because marine fuel oil usually contains a small amount of water , it is important to prime the bowl each time it runs, or otherwise,all the oil would passes over the side of the water outlet to waste.

The radius of the water outlet is greater than the fuel’s. There is a gravity disc within the water outlet, which did the work of controlling the radial position of the fuel- water interface.

As the fuel centrifuge operates, particulate matter accumulates on the bowl walls.

If the centrifuge is set as a clarifier, a mixture of water and solid material can form the particulate matter.
The free water is continually discharged if set as a purifier, thus the particulate matter must consist of solid material.

Notes:- In older machines it is important to stop the centrifuge to manually clean the bowl and the disc stack, but today most devices will discharge the contents of the bowl while the centrifuge operates.

Wikipedia