9.1 Engine Room Layout, Bilges, Tank Tops & Trainee Ratings Duties

9.1 Engine Room Layout, Bilges, Tank Tops & Trainee Ratings Duties

The marine engine room (machinery space) is the technical heart of a merchant vessel. It houses the massive propulsion engines, electrical power generation plants, steam boilers, fluid pumping networks, and auxiliary systems necessary to sustain ship operations across oceans. Unlike shore-based industrial plants spread across wide horizontal acreage, a ship's machinery space is constrained by the vessel's hull geometry. It is configured vertically across multiple structural decks or "flats" (platforms). This vertical architecture balances structural weight distribution, keeps the vessel's center of gravity low, provides positive gravity head for critical pumps, and facilitates the upward escape of exhaust gases and heat.

For a General Purpose (GP) Rating trainee under the Directorate General of Shipping (DG Shipping), Ministry of Ports, Shipping and Waterways, Government of India, engine room familiarization is of paramount importance. Trainees must understand the architectural levels of the engine room, identify machinery installations on each platform, master the techniques of manual bilge soundings and tank top housekeeping, and carry out disciplined machinery watchkeeping rounds alongside the duty engineer.

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1. Engine Room Architectural Hierarchy and Levels

Marine engine rooms are subdivided vertically into steel grated platforms or flats, interconnected by inclined steel companionway ladders and enclosed vertical escape trunks. The standard architectural progression from the vessel's keel upward comprises:

+-------------------------------------------------------------------------+
|               FUNNEL CASING & EXHAUST SKYLIGHTS                         |
| - Exhaust gas economizers, silencers, ventilation louvres               |
+-------------------------------------------------------------------------+
                                     |
+-------------------------------------------------------------------------+
|                      TOP PLATFORM (CYLINDER TOP)                        |
| - Main engine cylinder heads, exhaust valves, turbocharger, boilers     |
+-------------------------------------------------------------------------+
                                     |
+--------------------------------------------------+----------------------+
|             MIDDLE PLATFORM                      | ENGINE CONTROL ROOM  |
| - Diesel generators, starting air compressors,   | (ECR) & SWITCHBOARD  |
|   purifiers, central plate heat exchangers       | - Soundproof hub     |
+--------------------------------------------------+----------------------+
                                     |
+--------------------------------------------------+----------------------+
|             BOTTOM PLATFORM / TANK TOP           | WORKSHOP & STORES    |
| - Bedplate, crankshaft, thrust block, shafting,  | - Lathe, drills,     |
|   sea chests, cooling pumps, OWS, bilge wells    |   spare parts store  |
+-------------------------------------------------------------------------+
                                     |
                   [ DOUBLE BOTTOM TANKS & KEEL ]

• Bottom Platform (Tank Top Level): The lowest accessible level of the machinery space, resting directly above the inner bottom plating of the ship's double bottom tanks. It contains the heaviest mechanical running gear and fluid handling equipment.
• Middle Platform (Auxiliary & Treatment Flat): Located mid-height between the bottom floor plates and the cylinder tops. It accommodates intermediate machinery such as auxiliary diesel generators, starting air compressors, fuel/lube oil purifiers, and heat exchangers.
• Top Platform (Cylinder Cover Flat): Positioned at the level of the main engine cylinder heads. It provides access to high-temperature components, fuel injectors, exhaust valves, turbochargers, auxiliary oil-fired boilers, and waste heat economizers.
• Auxiliary Flats & Specialized Compartments:
  • Engine Control Room (ECR): A climate-controlled, acoustically insulated operations center typically situated at the middle or top platform level. It houses the Main Switchboard (MSB), power management consoles, automation monitoring screens, maneuvering levers, and alarm printers.
  • Workshop and Stores Flat: Houses machine tools (lathes, pedestal drilling machines, bench grinders, welding stations) and segregated storerooms for electrical spares, mechanical parts, and lubricating oils.
  • Steering Gear Flat: Located at the extreme after-end of the vessel, directly above the rudder stock, housing electro-hydraulic steering gear rams, hydraulic pumps, and the emergency steering position.
  • Funnel Casing and Exhaust Uptakes: The vertical trunk ascending from the top platform to the funnel top, encasing engine exhaust pipes, boiler uptakes, silencers, and ventilation dampers.

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2. Machinery Arrangement on Platforms

To ensure safe operation and efficient maintenance, machinery is grouped functionally across the platforms based on operating principles, weight, suction head requirements, and thermal dissipation.

Sea Chests: High Sea Suction versus Low Sea Suction

A critical exam topic for GP ratings is the distinction between High Sea Chests and Low Sea Chests located on the bottom platform:

• High Sea Chest: Located on the vessel's side shell plating well above the keel turn. It is used exclusively when navigating in shallow waters, rivers, estuaries, and during port stays. Drawing seawater from higher up prevents the cooling pumps from sucking up mud, silt, sand, and seabed debris that would choke strainers and erode pump impellers.
• Low Sea Chest: Located directly at the flat bottom shell plating adjacent to the keel. It is selected when navigating in deep, open waters at sea. During heavy weather, ship rolling and pitching can cause the high sea suction to emerge above the waterline, ingesting air and causing cooling pumps to lose suction cavitation. The low sea chest ensures continuous, uninterrupted submerged suction.

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3. Machinery Space Bilges, Tank Tops and Bilge Well Management

The lowest boundary of the machinery space is the tank top—the heavy steel plating that forms the top surface of the double bottom ballast and fuel tanks. Running along the forward, aft, port, and starboard corners of the tank top are recessed pockets known as bilge wells.

+-------------------------------------------------------------------------+
|                   ENGINE ROOM FLOOR PLATES (GRATING)                    |
+=========================================================================+
      |                                                     |             
      |           TANK TOP (INNER BOTTOM STEEL PLATING)      |             
+-----+-----------------------------------------------------+-----+       
|     |                                                     |     |       
|     |  +--------------------+    +---------------------+  |     |       
| P   |  |   DOUBLE BOTTOM    |    |    DOUBLE BOTTOM    |  | S   |       
| O   |  |   BALLAST TANK     |    |    FUEL OIL TANK    |  | T   |       
| R   |  +--------------------+    +---------------------+  | B   |       
| T   |                                                     | D   |       
|     |  +------------------+         +------------------+  |     |       
| B   |  |                  |         |                  |  | B   |       
| I   |  |   BILGE WELL     |         |   BILGE WELL     |  | I   |       
| L   |  | (Plain suction  |         | (Plain suction  |  | L   |       
| G   |  |  to mud box)    |         |  to mud box)    |  | G   |       
| E   |  +--------+---------+         +--------+---------+  | E   |       
+-----+-----------|----------------------------|------------+-----+       
                  | Striker Plate              | Striker Plate            
==================+============================+===================       
                     OUTER BOTTOM HULL PLATING (KEEL)                     

Bilge Sounding Protocol and Water-Finding Paste

Bilge wells collect natural condensation, minor gland weepage, cooler draining, and deck washings. Monitoring bilge levels is a statutory watchkeeping duty under STCW and DG Shipping guidelines.

1. Equipment: Use the ship’s designated calibrated rod or sounding tape and bob; a brass bob is common. Handle the equipment gently and follow the sounding procedure. Reduced-sparking materials lower friction-spark risk but do not eliminate ignition hazards.
2. Application of Water-Finding Paste: Bilge water frequently has a layer of dirty oil floating on its surface, which can coat the sounding rod and disguise the true water level. Apply a thin film of water-finding paste over the clean part of the rod or tape where the water level is expected. Extend the coated range if the entire film changes colour; otherwise a higher water boundary cannot be read. When lowered into the well, the paste reacts chemically with water, changing sharply from golden yellow to bright red/pink, while remaining unaffected by oil. This reveals the exact water-to-oil interface.
3. Taking the Sounding: The weighted rod is lowered smoothly down the sounding pipe until it gently touches the hardened striker plate welded at the bottom of the well. The tape is reeled up steadily, and the cut line is read in centimeters or inches.
4. Logging and Alerting: The measured levels are logged immediately in the official Sounding Book. Any sudden or abnormal increase in bilge sounding indicates a potential hull crack, ruptured seawater cooling pipe, fractured sea valve, or blown pump mechanical seal. The duty engineer must be alerted immediately.

Tank Top Housekeeping & Oily Waste Hazards

Keeping tank tops and floor plates dry, degreased, and spotless is not merely an aesthetic duty—it is a vital safety requirement:

• Class B Fire Prevention: Oil accumulations on tank tops exposed to hot exhaust manifolds, uninsulated steam lines, or electrical sparks create catastrophic machinery space fires.
• Corrosion Prevention: Stagnant bilge water containing sulfurous residues from heavy fuel accelerates electrolytic corrosion of the vessel's inner bottom structural steel.
• Personnel Safety: Oily floor plates cause severe slip and fall injuries among watchkeepers operating around moving machinery.
• Keeping Bilge Suctions Clear: Normal machinery-space bilge suctions lead through plain-ended tail pipes to accessible mud boxes with removable strainers. Loose rags, thread waste or packaging can obstruct the suction openings or strainer elements, reducing or stopping bilge pumping. Keep the wells and strainers clean and learn the ship’s approved arrangement; suction-end rose boxes are normally used in holds.
• Disposal of Oily Rags: Oily cotton waste and used wiping rags must never be tossed onto tank tops, behind pipes, or into open buckets. They are prone to spontaneous combustion. All used oily rags must be deposited immediately into dedicated, heavy-gauge steel drums fitted with foot-pedal operated, self-closing lids and subsequently incinerated or landed ashore under MARPOL Annex V.

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Safety During Dry-Docking

In dry dock, buoyancy support transfers to dock blocks so underwater hull work can be done. Docking is controlled by the dockmaster with the ship’s officers; follow their instructions and remain clear of restricted areas.

Shipyard work creates changing access routes, open hatches, suspended loads, temporary cables and simultaneous jobs. Attend the induction and toolbox talk, use the designated gangways, obey barriers and coordinate permits and machinery isolations with the ship/yard supervisors. A stop button alone is not energy isolation.

Learn the agreed alarm, off-ship muster point, escape routes and firefighting arrangements. Confirm with the responsible officer that fire protection remains available when normal services are disconnected. Report damaged temporary services, blocked access or unsafe work immediately; stop and seek instructions if conditions change.

4. Trainee GP Rating Machinery Watchkeeping Routine

At sea, merchant vessels operate on a 24-hour continuous watchkeeping schedule (traditionally organized into 4-hour shifts: 0000–0400, 0400–0800, 0800–1200, 1200–1600, 1600–2000, 2000–2400). A Trainee GP Rating assigned to the engine watch assists the Duty Engineer Officer and the Motorman/Oiler.

+-------------------------------------------------------------------------+
|          HOURLY MACHINERY WATCH ROUND - TRAINEE GP RATING               |
+-------------------------------------------------------------------------+
                                     |
   +---------------------------------+--------------------------------+
   |                                 |                                |
   v                                 v                                v
[ BOTTOM PLATFORM ]          [ MIDDLE PLATFORM ]              [ TOP PLATFORM ]
- Feel main bearings         - Check air receiver pressure    - Inspect cylinder exhaust
- Check thrust block temp      (maintain at 30 bar)             pyrometers (balanced)
- Sound all bilge wells      - Check purifier bowl speed &    - Check indicator cocks
- Inspect pump gland seals     operating water pressure       - Monitor scavenge air
- Inspect OWS & STP units    - Read LT/HT cooler temps          manifold pressure/temp
- Wipe floor plates &        - Sound HFO/MGO daily service    - Inspect boiler burner
  save-all drip trays          and settling tanks               flame & water glass

Watch Handover and Takeover

A trainee rating must arrive in the engine room 15 minutes prior to the start of the watch. Before formally accepting the watch, the rating must:

1. Check the general cleanliness and lighting across all platforms.
2. Visually inspect all bilge wells and tank tops for standing water or oil leaks.
3. Verify that running machinery sounds normal without unusual knocking, rattling, or squealing.
4. Check with the outgoing rating regarding any machinery undergoing maintenance, running fuel transfer operations, or active alarms.
5. Report any watch member’s apparent incapacity to the duty engineer. Do not assume duties while unfit or leave your station before proper relief; the outgoing officer must not hand over to an incapable relieving officer.

Hourly Watch Rounds Checklist

Every hour during the watch, the rating conducts a comprehensive physical round of all platforms, checking and reporting the following critical parameters to the duty engineer:

1. Main Propulsion Engine:
   • Exhaust Temperatures: Read each cylinder’s exhaust-temperature indication. Compare it with the normal value for the engine’s present load and its permitted cylinder spread. Report an abnormal temperature or changing imbalance to the duty engineer; possible causes include an injector fault, leaking exhaust valve or unequal cylinder loading.
   • Bearing Temperatures: Feel the crankcase inspection doors and bottom-end bearing housings by hand (or verify with an infrared non-contact thermometer). Sudden thermal rises indicate bearing wipe or oil film starvation.
   • Lubricating Oil Sump: Inspect the main engine bedplate sump dipstick and sight glasses. Ensure oil levels remain steady within prescribed operating limits. A sudden drop signals an external leak; a sudden rise indicates serious water contamination or fuel oil leakage into the crankcase.
   • Scavenge Manifold: Inspect the scavenge air space temperature (normally $40\text{--}50^\circ\text{C}$). Elevated temperatures accompanied by smoke at drains indicate a dangerous scavenge fire.
2. Auxiliary Diesel Generators:
   • Check generator lubricating oil sump levels, fuel rack positions, jacket water cooling temperatures ($80\text{--}85^\circ\text{C}$), and raw seawater cooling discharge pressure.
3. Starting Compressed Air Receivers:
   • Verify that the two main starting air receivers are fully charged to $30\text{ bar}$ pressure. Drain accumulated condensed moisture from the receiver bottom drain valves.
4. Centrifugal Purifiers:
   • Inspect purifier operating parameters: verify bowl rotational speed, fuel feed preheat temperature ($95\text{--}98^\circ\text{C}$ for heavy fuel oil), operating water pressure, and inspect clean fuel discharge sight glasses for clarity.
5. Fuel Settling & Daily Service Tanks:
   • Take manual soundings of the Heavy Fuel Oil (HFO) and Marine Gas Oil (MGO) settling and service tanks. Drain accumulated condensation and water from the spring-loaded self-closing bottom drain cocks into the funnel save-all.
6. General Housekeeping during the Watch:
   • Wipe down machinery casings, handrails, and drip trays using clean cotton rags.
   • Clean up any minor oil drops on floor plates immediately using degreaser and mops.
   • Verify that all fire doors and watertight doors remain fully closed.