The Engineering Diary

Types of Ships Cargo ships are classified into various types on the basis of purpose, size, type of cargo etc. The economic factor is of prime importance in designing a merchant ship. Every owner wants maximum return on their investment which means a ships construction not only depends on the current economic necessities but the factor of future adaptability also plays a part. From the preliminary design of a vessel due for construction, the following information can be obtained: 1.      Dimensions 2.      Displacement 3.      Stability 4.      Propulsive characteristics and hull form 5.      Preliminary general arrangement 6.      Principal structural details A layout of the various ship types and their subdivisions will be listed out, covering a wide range of all vessels in operation.  The type of ship plays an important role in deciding the above mentioned parameters. Types of Ships Ships a...

Gearing and tail shafts Vessels with low speed engines typically use direct drive from the crankshaft to the tail shaft with its propeller. Smaller domestic commercial vessels typically operate with high speed engines where direct drive shafts would revolve too fast to drag water across their propellers without efficiency losses due to cavitation (bubbling in the water flow). Consequently a gearbox is used to provide reduced speed of the shaft, reverse propulsion and through a clutch mechanism, disengaged propulsion. Gears and clutch mechanisms Principles of marine gear boxes Gearing is used in drive trains (sets of intermeshed gear wheels) to alter direction, position or speed/mechanical advantage of propulsion and auxiliary equipment such as winches, pumps and steering. The gear and shaft driven directly by the motor can be called the input and the final gear and shaft it drives can be called the output. Drive train A shown below illustrates reduction and reversal of the output, driv...

Maintenance Running checks should include: Gear box - oil level; inspect for leaks around casing; ensure pins and bolts in mechanical linkages are secure. Shaft bearings - check oil level in bearing sump; leakage through end seals; temperature of bearing. Stern gland - a leaking stern gland is a normal routine and is adjusted as a matter of course. See stern tubes in section above. Propeller shaft - check noise level to determine whether it is increasing. Regular maintenance schedules will include: Gearboxes - Adjust clutches and operating mechanism, clean filters and clean oil coolers. Drive train  Engine and shaft bearing moutings, loose shaft coupling bolts (perhaps due to mis-alignment) may need to be tightened. Mis-alignment of intermediate bearings will show up by overheating of the bearing. Survey servicing and repair schedules will include: Weardown survey- Allowance is determined by the manufacturer, but rules of thumb range from 3% of diameter as due for replacement to 6%...

Diesel fuel systems Direct supply The fuel tank with filler cap and venting breather is measurable by a sight gauge. Fuel is directed to the mechanical fuel pump through the supply line, along which primary and secondary filters ensure clean fuel only reaches the mechanical pump. Additional water separators are often fitted at the primary filter position. A manual lift pump is provided to assist bleeding (priming) the fuel line of trapped air after servicing the fuel filters. The cam driven mechanical pump forces the fuel to the injectors when it is required for combustion. Other fuel line components include: Baffle - They are fitted to prevent free surface effect. This affects the stability of the vessel and in extreme cases can cause vessels to capsize. Drain valve - is fitted to the lowest part of the tank. Its purpose is to drain water or sediment from the tank. A plug or cap is fitted so, if the valve vibrates open, the fuel is not lost or causes a fire risk. Water can be in the t...

Quick closing valves: What are Quick Closing Valves? On ships, marine diesel engines draw fuel from reservoirs or storage tanks which are also known as service tanks. All these tanks are provided with a specific valve known as quick closing valve, in order to shut the fuel supply in case of emergency such as fire. The closing of the valve can be done either manually, hydraulically or even by using compressed air. A typical arrangement consists of wire operated valves with wire pull livers located externally to the machinery space. If you want to know more about other types of valves, read these articles about gate valves, globe valves and butterfly valves. Construction and Working Quick closing valve is a kind of pressure reducing valve in which the an automatic process control valve for fluid pressure control is used for unmanned machinery spaces. This can be done by careful selection of valve trim, i.e. the parts of the valve that come in contact with the controlled fluid and form an...

What is a Ship's Stern Tube? Everyone knows that a ship is propelled with the help of a propeller located at the aft of the ship. However, they may not know how the propeller is connected to the engine located inside the ship. A stern tube, situated at the aft of the ship, helps in this purpose. The propeller is the only part of ships machinery, apart from the rudder, that is located outside the ships engine room. Have you ever seen the propeller of a ship and wondered how it is connected to the inside of the ship? Have you ever wondered where the shaft holding the propeller goes when it vanishes into the ships hull? If so, then you have come to the right place. The propeller, a part of the propulsion system of the ship, needs a power source to rotate it. A marine diesel engine located inside the ship supplies the power to the propeller. Both the diesel engine and propeller are very heavy: locating them both at the same place inside the ship would disturb the ships stability. It is...

Principles of internal combustion engines Operating principles Combustion is the process in which fuel heated beyond its flash point ignites and gives off energy and the waste products as exhaust gasses (carbon dioxide, carbon monoxide and water). The three elements necessary for combustion (or fire) are: Oxygen + Heat + Fuel = Explosion or Fire Internal combustion engines suck in air to access the oxygen and use hydrocarbon fuels including petrol, diesel and liquid propane gas. The internal combustion process Internal combustion engines use successive explosions of atomised air and fuel mix to force a piston down a gas tight internal cylinder. The piston is connected through a big end bearing to a cranked shaft that is weighted by a flywheel to assist its rotary momentum. Thus with three primary moving parts (piston, connecting rod and crankshaft) the pistons reciprocating motion drives the crankshafts rotary motion. A sturdy metal casting of an engine block holds the internal parts a...