Turning gear

A Jacking gear (also known as a Turning gear) is a device placed on the main shaft of an engine or the rotor of a turbine. The jacking gear rotates the shaft or rotor and associated machinery (such as reduction gears and main turbines), to ensure uniform cool-down. Without turning, hogging or sagging can occur. Additionally, the jacking gear's assistance in rotation can be used when inspecting the shaft, reduction gears, bearings, and turbines. As an auxiliary function, the jacking gear also helps to maintain a protective oil membrane at all shaft journal bearings.

Hogging is when the shaft bows upwards due to thermal stratification.

On the engine shaft of a marine vessel, this process also prevents the shaft from warping when a ship is preparing to achieve maneuvering status.

Thrust block

A thrust block, also known as a thrust box, is a specialised form of thrust bearing used in ships, to resist the thrust of the propeller shaft and transmit it to the hull.

Early screw-propelled steamships used a thrust block or thrust box composed of perhaps a dozen lower-rated plain thrust journal bearings stacked on the same shaft.[These were problematic in service: they were bulky, difficult to dismantle, wasted power through friction and they had a tendency to overheat. The thrust box was built of a box-like cast iron housing with a radial bearing at each end and a number of collars formed on the shaft between them.This shaft was often a short section of removable shaft called the thrust shaft, linking the engine ahead to the propeller shaft astern. A series of iron horseshoe-shaped collars fitted over the small diameter of the shaft and bore against the forward face of the shaft's collars. Each horseshoe was faced with a low-friction pad of babbitt metal. Lubrication was by an oil bath in the box and a plentiful volume was important for cooling purposes too.

Although lignum vitae wood was used for the radial stave bearings in the stuffing box, cooled directly by seawater itself, this material wasn't capable of withstanding the force needed for the thrust blocks of any but the earliest screw vessels.

Each horseshoe was independently adjustable forwards and back, by either wedged gibs or a screwed adjustment. A particular problem with these thrust boxes was in adjusting them so that the force was shared equally between all the collars. Adjustment was often done on the basis of their operating temperature, gauged with the engineer's hand.


Improved understanding of the theory of lubrication films (initially by Reynolds) allowed the development of much more efficient bearing surfaces. This allowed the replacement of multiple collars in a thrust box by a single thrust block.

Fluid-film thrust bearings were invented by Australian engineer George Michell who patented his invention in 1905. Michell bearings contain a number of sector-shaped pads, arranged in a circle around the shaft, and which are free to pivot. These create wedge-shaped films of oil between the pads and a rotating disk on the shaft. Each lubricant "wedge" can only be of a limited length (in the direction of travel, i.e. circumferential) so multiple pads are needed rather than a single ring. No lubrication pump is needed, the rotation of the shaft itself is sufficient.

Strait

A strait is a naturally formed, narrow, typically navigable waterway that connects two larger bodies of water. It most commonly refers to a channel of water that lies between two land masses, but it may also refer to a navigable channel through a body of water that is otherwise not navigable, for example because it is too shallow, or because it contains an unnavigable reef or archipelago.



strait of malaca


Straits used for international navigation through the territorial sea between one part of the high seas or an exclusive economic zone and another part of the high seas or an exclusive economic zoneare subject to the legal regime of transit passage (Strait of Gibraltar, Dover Strait, Strait of Hormuz). The regime of innocent passage applies in straits used for international navigation (1) that connect a part of high seas or an exclusive economic zone with the territorial sea of coastal nation (Strait of Tiran, Strait of Juan de Fuca, Strait of Baltiysk) and (2) in straits formed by an island of a state bordering the strait and its mainland if there exists seaward of the island a route through the high seas or through an exclusive economic zone of similar convenience with respect to navigational and hydrographical characteristics (Strait of Messina, Pentland Firth). There may be no suspension of innocent passage through such straits.

What is difference between MC and MC-C engine in MAN B&W???

These are the physical differences between the two.

The first MC-C engines to be introduced in 1988 were K80MC-C and K90MC-C engines. They were almost identical to the MC engines of the time, but the layout was optimised for container vessels (at that time the -C stood for "container"). I 1994 the K98MC-C engine was added to the programme.

In 1996 and onward the MC-C versions of the small and medium bore engines were added to the programme. In this case the -C stands for "compact", as the engines were intended to be lighter, cheaper and yet more powerful. They feature an integrated camshaft housing, simplified cross-head and a variety of other smaller changes to facilitate the "compact" concept. In exchange the fuel injection system was simplified and the VIT system was made an option. The small and medium bore MC-C engines are thus best suited to vessels operating for prolonged periods at the power at which the engines are optimised.

The engine types prior to the introduction of the MC-engines were designated e.g. EF, FF, GF, GFCA, GB. The first letter was an indication of the mean pressure, while the subsequent letters were an indication of the application and turbo charger efficiency. This system was increasingly difficult to maintain as the engines were being developed and it had earlier been decided to reduce the designation to two letters. Some letters were already in use to designate stroke or used in 4-stroke designations. It was thus decided to name the new engine type MC, where M indicates the mean pressure (but not strictly according to the previous system) and the C indicated the turbo charger efficiency. This was at the same time the last engine designation according to the old system.


MC-C is more compact and produces more power compared to an MC engine.

Tonnage- Net tonnage, Gross tonnage, Gross Register Tonnage (GRT) and Net Register Tonnage (NRT)

Gross tonnage (GT) is a function of the volume of all ship's enclosed spaces (from keel to funnel) measured to the outside of the hull framing. The numerical value for a ship's GT is always smaller than the numerical values for both her gross register tonnage and the GRT value expressed equivalently in cubic meters rather than cubic feet, for example: 0.5919 GT = 1 GRT = 2.8316 m³; 200 GT = 274 GRT = 775,88 m³; 500 GT = 665 GRT = 1,883.07 m³; 3,000 GT = 3,776 GRT = 10,692.44 m³), though by how much depends on the vessel design (volume). There is a sliding scale factor. So GT is a kind of capacity-derived index that is used to rank a ship for purposes of determining manning, safety and other statutory requirements and is expressed simply as GT, which is a unitless entity, even though its derivation is tied to the cubic meter unit of volumetric capacity

Gross register tonnage (GRT) represents the total internal volume of a vessel, where a register ton is equal to a volume of 100 cubic feet (2.83168 m³), which volume, if filled with fresh water, would weigh around 2,800 kg or 2.8 tonnes. The definition (and calculation) of the internal volume is complex; a ship's hold can, for instance, be assessed for bulk grain (accounting for all the air space in the hold) or for bales (omitting the spaces into which bulk, but not baled cargo would spill). If V stands for the total internal volume in m³, then the GRT equals V / 2.83168, so for a ship of 10,000 m³total internal volume, the gross register tonnage is 10,000 / 2.83168 = 3531.47 GRT. Gross register tonnage was replaced by gross tonnage in 1994 under the Tonnage Measurement convention of 1969, and is no longer a widely used term in the industry.

Net register tonnage (NRT) is the volume of cargo the vessel can carry; i.e., the gross register tonnage less the volume of spaces that will not hold cargo (e.g., engine compartment, helm station,crew spaces, etc., again with differences depending on which port or country is doing the calculations). It represents the volume of the ship available for transporting freight or passengers. It was replaced by net tonnage in 1994, under the Tonnage Measurement convention of 1969.

What is condensate treatment in boiler?how condensation will take place?

we have a dump condenser using sea water. it cools the bypassed steam from dump valve, From heater, steam trap sends only condensate to the hotwell. In this hotwell we add certain chemicals like phospates,alkanline materials, oxygen scavengers such as hydrazine, coagulants to bind all precipated salts in order to prevent deposition so that which can be extracted during blow down.

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Main Engine cooling system V/S Auxiliary engine cooling

The cooling water pump which may be engine driven or be a separate electrically driven pump pushes the water around the circuit. After passing through the engine, where it removes the heat from the cylinder liners, cylinder heads, exhaust valves and sometimes the turbochargers, it is cooled by seawater and then returns to the engine. The temperature of the cooling water is closely controlled using a three way control valve. If the water is allowed to get too cold then it will cause thermal shocking which may lead to component failure and will also allow water and acids to condense on the cylinder bores washing away the lubricating film and causing corrosion. If it gets too hot then it will not remove the heat effectively causing excessive wear and there is a greater danger of scale formation. For this reason the cooling water outlet temperature is usually maintained at about 78-82°C. Because it is at a higher temperature than the cooling water used for other purposes (known as the LT cooling), the water for cooling the engine is known as the HT (High Temperature) cooling water.

Main engine cooling system

Auxilliary engine cooling system.

Cooling can be achieved by using a dedicated cooler or by mixing in some of the water from the LT cooling circuit. The LT cooling water is then cooled in the sea water coolers. The temperature is controlled using cascade control which monitors both the inlet and outlet temperatures from the engine. This allows a fast response to any change in temperature due to a change in engine load.

To make up for any leaks in the system there is a header tank, which automatically makes up any deficiency. Vents from the system are also led to this header tank to allow for any expansion in the system and to get rid of any air (if you are familiar with a domestic central heating system then you will see the similarities). The header tank is relatively small, and usually placed high in the engine room. It is deliberately made to be manually replenished, and is fitted with a low level alarm. This is so that any major leak would be noticed immediately. Under normal conditions, the tank is checked once per watch, and if it needs topping up, then the amount logged.

The system will also contain a heater which is to keep the cooling water hot when the engine is stopped, or to allow the temperature to be raised to a suitable level prior to starting. Some ships use a central cooling system, whereby the same cooling water is circulated through the main engine(s) and the alternator engines. This system has the advantage whereby the engines which are stopped are kept warm ready for immediate starting by the engines which are running.

A fresh water generator (FWG) which is used to produce fresh water from sea water is also incorporated.

A drain tank has been included. This is for when the engine is drained down for maintenance purposes. Because of the quantities of water involved and the chemical treatment, it is not economically viable or environmentally responsible to dump the treated water overboard each time. This way the water can be re used.

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