IMPORTANT SYSTEMS ONBOARD MERCHANT SHIPS
FRESH WATER COOLING SYSTEM
For cooling important machinery without the danger of corrosion, and dump the heat to sea water system. This system is a closed loop, the same water circulated after cooling by heat exchangers.
SEA WATER COOLING SYSTEM
For cooling various machinery and dump the heat to the sea.
LUBRICATING OIL SYSTEM
Lubricating oil reduces friction where machinery parts are in relative motion and takes away the heat produced by friction. This is also a closed loop arrangement, the oil cooled by heat exchangers using seawater or freshwater as the cooling medium.
HYDRAULIC OIL SYSTEM
This system conveys energy in the form of hydraulic pressure and flow, for running various machinery such as power packs, mooring winches, cranes, etc.
COMPRESSED AIR SYSTEM
Air is compressed and stored in air bottles (30 BAR). It is mostly used for starting internal combustion engines. After reducing through reducing valves the low pressure air is used for controllers,cleaning,pneumatic tools,whistle, etc. (6.5BAR)
FUEL OIL SYSTEM
Fuel oil for main and auxiliary engines and boiler is taken from ashore and stored in ship’s double bottom tanks (called bunkers). The oil is then transferred to settling tanks using a transfer pump and heated. From settling tank, oil is centrifuged and stored in service tank, from which the users draw it. The lines are provided with valves and filters to clean and control the flow. A separate diesel oil system is also present, for use where low viscosity fuel is required.
Sea water is pumped into the ballast tanks and is pumped overboard or transferred to other ballast tanks as and when required for maintaining the stability of the ship. Two ballast pumps and an eductor(or stripper pump) is used for the purpose.
Bilge means waste water and oil/water mixture, which accumulates in bottom of enclosed spaces of the ship. This has to be pumped overboard using a pump and oil removing device (oily water separator). Accumulation of bilges will lead to serious stability and safety problems. Bilge pump has suctions from all machinery and cargo spaces. The piping system consists of filters (strum boxes) , valve chests, individual valves, bilge well high level alarms etc.
FRESH AND SEA WATER HYDROPHORE SYSTEMS
These systems are almost identical. Potable water is taken from storage tanks and pumped into a pressure vessel against an air cushion (charged from low pressure air line) and is circulated in the accommodation for consumption, and engine room for make-up feed water for engine cooling system and boiler. A branch is taken through a heater (steam or electric heating coils named calorifier) and piped into accommodation for hot water requirement. Similarly sea water is pumped from main sea water line and through another pressure vessel, piped into toilets for flushing out. The water thus flushed out (grey water) is collected in a sewage treatment plant and is pumped overboard automatically after cleansing it. Some ships have a vacuum type toilet system which uses minimum fresh water, thus reducing corrosion, yet costly to install and maintain.
All ships are having the accommodating and engine control room air conditioned, and have cold rooms to store food material. Freon systems are closed loop systems, the compressor compressing gas and this gas at critical pressure is cooled in a seawater cooled condenser, making it into liquid. The liquid is passed through an expansion valve(throttling) into the evaporator coils, where it is expanded to gaseous from by absorbing outside heat, which is provided by blowing air by a fan. In cold weather, a heating coil which is mounted beside evaporator is operated for heating the air. Similarly domestic fridge has the same system, only difference being different expansion valve settings are used to maintain different temperature in chambers as per requirement.
BOILERS AND FEED/STEAM SYSTEM
Ships use steam either for main & auxiliary prime mover, or for heating and drive cargo oil pump (COP) turbines. The closed loop system comprises of a boiler, which converts water into steam, machinery/heater etc. which consume heat energy and resultant steam and water cooled in a condenser, which is collected in a hotwell and pumped back into the boiler. The system incorporates various valves, piping, steam traps, drain cocks etc. In tankers the boiler flue gas is cooled, cleaned and used as inert gas (IG) for inerting the cargo tanks.. Boilers are either oil-fired (donkey boilers) and are exhaust gas heated while sailing. (lamont boilers). Usually a combination is used. Boilers are fully automated, and are fitted with double safety valve with an easing gear for manual operation.
Ships are having a dedicated pumping system for pumping sea water into a ring main around the ship. The system has quick release/connect type valve (hydrants) into which fire hoses can be connected quickly. There are two fire pumps and an emergency fire pump situated in a space other than engine room. There is an isolating valve after the engine room for isolating the engine room from the rest of the vessel. Passenger ships are fitted with a sprinkler system which is similar to hydrophore system, viz a pressure tank and auto-start pump for keeping system pressure. Sprinklers are actuated by presence of smoke/fire in the compartments. An international shore connection is held on ship, so that water from outside can be connected to pressurize the fire mains.
Steering gear is situated in the steering flat. It is controlled from the navigating bridge either hydraulically or electrically. The system consists of hydraulic oil tanks, variable delivery pumps, rams that drive the rudder through a cross-head, a set of valves for bypassing and safety, high pressure piping, connecting hydraulic or electric control lines, emergency controls etc. In the rotating vane system, delivery pumps and control systems differ in the manner of working.
PROPELLER SHAFT SEALING SYSTEMS
Most ships are having an enclosed type oil filled stern tube, sealed at both ends by sets of lip seals to the attached chrome/ceramic liners, the gravity tank that keeps oil pressure above seawater pressure outside. The height of oil column in the tank has to be adjusted according to vessel's draught for effective sealing.
Usually a 2 stroke, multi cylinder reversible diesel engine working on dual cycle, connected to the propeller shafting through a thrust bearing (michell thrust block). New generation engines are capable of burning heavy fuels with density >1. The engine has fuel, lube, cylinder oil, piston cooling oil, cooling water, starting air, scavenge air, exhaust gas manifolds fitted onto it. They can be maneuvered from engine control room, engine side and navigation bridge. All oil and water are pumped by separate motor driven pumps, are piped in a closed loop manner. They are fully automated and needs regular planned maintenance system.
This system consists of a battery of CO2 cylinders that are connected to a common manifold, which can be opened to engine room or cargo holds. In case of a serious fire, the compartment affected is sealed and required number of CO2 bottles released, thereby flooding the compartment with CO2. The bottle battery is kept in a dedicated chamber (CO2 room) , and control via a pilot bottle operated servo piston which pulls the bottle valves is provided in a station other than affected areas/CO2 room. There are alarm systems for warning before gas is released and a head-count has to be taken before action. Alternately old ships were having halon as the fire extinguishing medium, but it has been phased out due to new regulations. Fire extinguishers of various types and capacities are kept in the ship at easily accessible places. Fire alarm system has sensors of different type and manual operating push buttons are also provided for locating origin of fire.
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