The operation of onboard machinery ships requires specialised theoretical knowledge. For every engineering officer, a practical understanding of shipboard operations is essential for taking cognizance of complicated machinery operations and system integrations. Engineers in their first stint onboard must follow a hierarchy on board to define and demand piping diagrams in order to have a thorough understanding of different symbols and lines from facsimiles provided.

A typical line diagram resembles a maze and can be difficult to interpret. For this reason, it is advisable to trace the lines on paper rather than solely relying on tracing them in your mind. The junior engineer is responsible for all sludge and bilge water transfers in accordance with the directions of the second engineer, who is in charge of this area of the ship's operation. The line diagrams in plumbing systems are instigated by starting with the highest or lowest point in the system, specifically with a tank that supplies water or is being drained.

Figure 1: A basic line diagrams systems on boardship

A tank should be marked with its outlet and inlet valves, as well as any sophisticated remote closing devices that have pneumatic controls for operations external to the engine room. Tanks should be equipped with pipes for air, thermometers to measure temperature, gauges to measure levels and overflow pipes. These should also be fitted with electronic alarms for high and low levels. When soundings are taken in tanks, the pipes used to measure depth must be carefully positioned, whether they are placed in the aft or forward part of the tank.

Manhole covers and other supports facilitate the cleaning and inspection of various tanks. These items must also be shown with a symbol representing important details. The locations of mounting brackets provide an additional method of determining a system's condition and operating parameters. When a problem occurs, maintenance personnel can deal with it quickly by comparing the actual location of the brackets to the markings that indicate their proper placement. It is important to note the point where the pipes leave the tank. In addition, the lines should be traced with their subsequent valves marked with their types. This will enable you to know the leakages and rectify them at the earliest.

A careful inspection of the steam lines and valves should be made, as they are a potential source of injury. The valves placed below floor plates can be difficult to identify and memorize, and thus should be marked with names from a diagram by means of a felt tip pen for future reference.

Additional parts of the pump, including strainers and filters, should be marked clearly. The change-over lever on the duplex filter should be observed closely, as should its purging cock and drain. 

It is important to consider the type of pump along with its application in handling different fluids in a particular system. One should study the reasons for their application in that system, and frame a rationale for those reasons. Relief valves, which are not generally found on centrifugal or rotodynamic pumps, should be looked upon as part of the discharge side of a pump.

Method

The following steps should be taken to construct a line diagram system:

1. Always start from the highest or lowest point, never from a midpoint.
2. Ensure you are aware of the colour coding for various piping systems on a ship, such as bilge lines are normally yellow, sludge lines are black, fresh water lines are blue, and seawater lines are green.
3. Wear all personal protective equipment including a helmet, gloves, and safety shoes when conducting site surveys. Be aware that you may need to go below the floor plate in areas where space is limited.
4. Always carry a flashlight when tracing a pipe, because a line being traced may cross another pipe in dark corners or under the bilge area below the floor plate.
5. Valves are important components of machinery. Knowing the different types of valves and their symbols will help you understand how machinery works.
6. Any crossover or overlapping line must be clearly shown in the diagram. Crossover lines are connected to each other and overlapping lines do not touch. Each crossover or overlapping line must be clearly indicated in the diagram by being connected to the same line or by not touching other lines. The line usually indicates a gap or break in the data. A jump curve or half circle is used when it is not connected to the below line.
7. Place the position of forwarding, aft, port and starboard in the diagram. These are very important in identifying the location of objects within the diagram.
8. When tracing the line, make sure to draw the diagram in rough hands. After you have completed the tracing, transfer it onto a neat piece of paper with an approximate scale.
9. Compare your diagram with the one in the ship's library.
10. After checking the diagram, compare your observations with those on the ship. If you see any discrepancy, verify it with the crew. Ships often undergo modifications which are not included in the original diagram.
11. If you find any modification necessary, please mark it on the line diagram.
12. Never try to draw more than one system in a single diagram.
13. Make sure a senior officer has reviewed the diagram you have drawn to avoid errors.

All systems have specific intricacies that must be considered when determining the components and processes involved. The fuel oil system, for example, is made up of four main parts: bunkering, fuel oil transfer systems, cleaning and separation systems, and the fuel supply system (boiler, main engine, generator). In general, one should start by drawing cushy diagrams. Then one should work on the fuel supply system, which is integrated into the machinery; for example, fuel supply lines in the main engine generator engine or boiler firing line.

Figure 2: A fuel oil diagram system

The seawater cooling line is easy to miss, but it is important not to overlook the mounting on the sea chest filter, which has a distinct cock to purge off the air before it enters the system. Three-way valves in a particular system, such as a cooling freshwater system, also must be paid attention to, and their functions studied, with an emphasis on the type of control involved in their operation.

The computer-based training can also be used as a source of potential knowledge and concepts, which should be studied prior to tracing the lines physically if provided. In order to prevent any injury or damage, it is important that valves do not manipulate the systems while tracing procedures are being carried out. This is particularly important for junior engineers.

Once the systems are drawn, they should be verified with the senior engineers. When the drawings are complete, they can be understood in detail with operations and transfers. A rational approach using theoretical concepts can be carried out on paper if one is disciplined enough.

Reading and understanding line diagrams is a fundamental part of understanding the mechanics of machinery operations; it should be followed in order to master the art of reading line diagrams.

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