Section 2.3 Bilge Systems and Pumping Arrangements

The bilge system is a critical safety feature on any vessel, designed to remove accumulated water from various compartments, primarily cargo holds and machinery spaces. On bulk carriers, given the nature of their cargoes and the potential for water ingress (from sweat, minor hatch leakage, or more serious breaches), an effective bilge system is paramount for protecting cargo, maintaining stability, and ensuring the overall safety of the vessel. This system must also operate in strict compliance with environmental regulations (MARPOL Annex I) when dealing with oily bilges from machinery spaces.

1. Purpose of Bilge Systems:

1. Remove Water from Cargo Holds:
   1. Cargo Sweat/Condensation: Changes in temperature and humidity can cause condensation on the ship’s structure within the holds or on the cargo itself, leading to water accumulation.
   2. Minor Leakage: Small amounts of water might enter through hatch cover seals (if not perfectly weathertight), ventilation openings, or minor structural defects during heavy weather.
   3. Cargo Drainage: Some cargoes may release water during the voyage.
   4. Hold Washing Water: After hold cleaning operations, residual wash water needs to be removed.
2. Remove Water from Machinery Spaces:
   1. Minor leaks from pumps, pipes, coolers, or machinery.
   2. Drainage from various equipment.
   3. Accumulation from stern tube seal leakage (though this is usually managed separately). This water in machinery spaces often becomes contaminated with oil, forming “oily bilge water,” which requires special handling.
3. Remove Water from Other Compartments: Void spaces, chain lockers, bow thruster rooms, steering gear compartments, and other dry compartments are typically fitted with bilge suctions.
4. Emergency Dewatering: In case of minor flooding due to hull damage or pipe fracture, the bilge system can provide a limited dewatering capability, though it is not designed for major damage scenarios (where dedicated salvage pumps would be needed).

2. Components of a Typical Bilge System:

1. Bilge Wells:
   1. Cargo Holds: Small, recessed sumps (wells) located at the lowest points of each cargo hold, usually at the aft end (and sometimes forward end). They are designed to collect water that drains across the tank top.
   2. Machinery Spaces: Bilge wells are strategically located in the engine room tank top to collect leakages.
   3. Other Compartments: Similar wells or low points are provided in other spaces served by the bilge system.
2. Strum Boxes (Rose Boxes / Strainers):
   1. Perforated metal boxes or plates fitted over the suction inlet in each bilge well.
   2. Purpose: To prevent solid debris (cargo residues, rags, dirt, rust scale) from entering the bilge lines and choking the pumps or valves. The perforations must be small enough to stop damaging debris but large enough not to get easily clogged. Regular cleaning of strum boxes is essential.
3. Bilge Lines (Piping):
   1. A network of pipes connecting the bilge wells in various compartments to the bilge pumps.
   2. Materials: Typically steel, sometimes galvanized.
   3. Arrangement: Usually a main bilge line runs through the vessel (often in a duct keel or pipe tunnel in bulk carriers) with branch lines leading to each bilge suction.
   4. Segregation: Regulations (SOLAS) require that the bilge pumping system for machinery spaces is separate from that serving cargo holds, or that arrangements are made (e.g., via non-return valves and spectacle flanges/spool pieces) to prevent any accidental pumping of oil-contaminated water from machinery spaces into cargo holds, or vice-versa, especially if a cargo hold bilge pump can also take suction from the engine room.
4. Bilge Pumps:
   1. Main Bilge Pump(s): Usually located in the engine room. These can be centrifugal, reciprocating, or screw pumps. SOLAS requires at least two independently powered bilge pumps for cargo ships (one of which may be driven by the main engine).
   2. Emergency Bilge Pump: Some vessels may have a dedicated emergency bilge pump, often located outside the engine room, with its own power source, capable of taking suction from machinery spaces in case of flooding.
   3. Cargo Hold Bilge Pumps (if separate): Some bulk carriers might have dedicated pumps for cargo hold bilges, especially if there’s a desire to keep these systems entirely separate from oily machinery space bilges.
   4. Eductors: Venturi-type devices that use a flow of motive water (e.g., from a fire pump or ballast pump) to create suction and draw water from bilge wells. Often used for stripping or in smaller compartments. They have no moving parts in contact with the bilge water, making them less prone to clogging.
5. Valves:
   1. Bilge Suction Valves (Master Valves / Distribution Valves): Located on the branch lines from each bilge well, allowing selection of the compartment to be pumped. These are often grouped in a bilge manifold.
   2. Non-Return Valves (Check Valves): Fitted in the bilge lines to prevent backflow of water into a compartment that has just been pumped, or to prevent accidental flooding of one compartment from another via the bilge line. These are critical for the system’s integrity.
   3. Overboard Discharge Valve: For discharging clean bilge water (e.g., from cargo holds containing non-polluting cargo, or after hold washing with clean water) directly overboard, where permitted. This valve must be carefully controlled and secured to prevent illegal discharges.
6. Oily Water Separator (OWS) / Oil Filtering Equipment (OFE):
   1. Mandatory Requirement (MARPOL Annex I): All ships over 400 GT must be fitted with an OWS or OFE to treat oily bilge water from machinery spaces before it can be discharged overboard.
   2. Operation: The OWS separates oil from water, typically to achieve an oil content in the effluent of less than 15 parts per million (ppm).
   3. Components: Often includes a coarse separating chamber, fine separating elements (coalescers), and an oil content meter (OCM).
   4. Oil Content Meter (OCM): Continuously monitors the oil content of the OWS effluent. If the oil content exceeds 15 ppm, the OCM automatically triggers an alarm and diverts the flow back to a bilge holding tank or slop tank, preventing illegal discharge. The OCM must be type-approved and regularly calibrated.
7. Bilge Holding Tank / Sludge Tank:
   1. Tanks used to store oily bilge water or separated oil (sludge) from the OWS before it can be disposed of legally (e.g., to shore reception facilities or by incineration if an approved incinerator is fitted).
8. Standard Discharge Connection (MARPOL):
   1. A universal connection point on deck for discharging oily residues and sludge to shore reception facilities.

3. Operation of the Bilge System:

1. Routine Pumping:
   1. Bilge levels in various compartments should be sounded/checked regularly (e.g., daily or per watch).
   2. When pumping is necessary, the correct suction valves are opened, the pump is started, and the discharge is directed appropriately (e.g., clean water overboard where permitted, oily water to the OWS or holding tank).
   3. Monitor pump operation (pressures, flow) and ensure the compartment is effectively emptied.
   4. After pumping, close all valves securely.
2. Pumping Machinery Space Bilges:
   1. This must be done via the OWS.
   2. The OWS must be operated according to the manufacturer’s instructions and MARPOL regulations.
   3. The OCM must be operational and its readings monitored.
   4. All operations (start/stop times, quantities, OCM readings, overboard discharge or transfer to holding tank) must be meticulously recorded in the Oil Record Book (ORB) Part I. This is a legally binding document and subject to intense scrutiny by authorities.
3. Emergency Pumping:
   1. In case of flooding, the bilge system can be used for dewatering, but its capacity is limited. The Master must assess the situation and prioritize which compartments to pump.
   2. Ensure non-return valves are functioning to prevent inter-flooding between compartments.

4. Maintenance of the Bilge System:

1. Strum Boxes: Clean regularly, especially before and after carrying cargoes that produce fine residues, and after hold washing. Clogged strum boxes render the bilge suction ineffective.
2. Pumps: Regular inspection, lubrication, checking of seals/packing. Overhaul as per PMS.
3. Valves: Operate all valves regularly to prevent seizure. Inspect for leakage. Ensure non-return valves are free and seating correctly (often a common source of problems).
4. Piping: Inspect for corrosion and leakage. Sounding pipes for bilge wells must be kept clear.
5. OWS/OFE: This requires diligent maintenance as per the manufacturer’s manual. This includes:
   1. Regular cleaning of filters, coalescers, and separating chambers.
   2. Calibration of the OCM by an approved technician at intervals specified by regulations (typically every 5 years or after any repair/replacement that could affect its accuracy). Onboard operational checks of the OCM alarm and diverting functions should be done frequently.
   3. Checking and cleaning of sensors and probes.
6. Bilge Alarms: High-level alarms in bilge wells (especially in machinery spaces and unattended compartments) must be tested regularly.
7. Oil Record Book Entries: While not direct maintenance of the system, accurate and truthful entries in the ORB are paramount. Falsification of the ORB carries severe penalties.

Analysis for the Master (Bilge Systems): The bilge system is crucial for both routine water management and emergency response. Its correct operation and maintenance are vital, with significant regulatory implications.

1. Safety: An ineffective bilge system can lead to cargo damage, loss of stability (due to free surface effect from accumulated water), or, in extreme cases, contribute to the loss of the vessel. The Master must ensure the system is always ready for use.
2. MARPOL Compliance: This is a major area of focus for PSC inspections.
   1. The OWS must be type-approved, fully operational, and used correctly.
   2. The OCM must be functional and calibrated.
   3. The Oil Record Book Part I must be accurately maintained, with no discrepancies between recorded discharges and the vessel’s actual operations or tank capacities. “Magic pipes” or any illegal bypass of the OWS are strictly forbidden and will result in severe penalties for the ship, company, Master, and crew involved.
   4. The Master must foster a culture of strict adherence to MARPOL and ensure all crew understand the legal and environmental consequences of illegal discharges.
3. Training and Familiarization: Deck and engine crew must be thoroughly familiar with the layout of the bilge system, the location of all valves and suctions, the operation of pumps and the OWS, and the procedures for bilge pumping from all compartments.
4. Regular Testing and Drills: Include bilge pumping (especially emergency bilge suction from the engine room) in routine emergency drills.
5. Cargo Hold Bilges: For bulk carriers, ensuring cargo hold bilge suctions are clear and effective is vital, especially when carrying cargoes prone to sweating or if heavy weather is anticipated. Contamination of sensitive cargoes by water from adjacent holds (if non-return valves fail) is also a risk.
6. Record Keeping: Apart from the ORB, maintain records of bilge system maintenance, OWS servicing, and OCM calibrations.

The bilge system, while often operating in the background, is a cornerstone of a vessel’s safety and environmental compliance. The Master’s diligence in ensuring its proper functioning, the crew’s adherence to operational and maintenance procedures, and an unwavering commitment to pollution prevention are essential.