Operational Guide · Registers & Logbooks

# Bilge Water Management

Discharging bilge water through the oily water separator (OWS): the procedure most exposed to illegal tampering.

bilge bilge water OWS 15 ppm MARPOL Annex I

## Operational Explanation

Bilge water collected in the machinery space contains traces of oil from leaks, condensation and washings. Before discharge at sea it must pass through the Oily Water Separator (OWS), which must ensure an oil content not exceeding 15 ppm (parts per million), with an alarm and automatic stoppage of the discharge if this is exceeded.

## Regulatory Reference

MARPOL Annex I, Regulation 14 (oil/water separating equipment) and Regulation 15 (control of operational discharges of oil). Corresponding ORB codes: D (non-automatic discharge) and E (automatic discharge).

## Scope of Application

All ships of 400 GT and above must be fitted with a type-approved OWS; smaller ships with such equipment on board are nonetheless subject to the same discharge limits.

## Procedure / How to Complete It

1. Verify that the OWS is operating and correctly calibrated before every discharge.
2. Start the discharge only while the ship is under way, at a distance from the coast within the applicable limits (outside Special Areas, unless stricter conditions apply).
3. Continuously monitor the alarm/shutdown system (Oil Discharge Monitoring and Control System, ODMCS) during the discharge.
4. If the alarm activates, the discharge stops automatically: never manually force a bypass.
5. Record the operation in the ORB (code D or E) with quantity, position and confirmation that the system operated correctly.

## Practical Example

Example of a code E entry: "Automatic bilge water discharge via OWS, 4.2 m³, position 41°12'N 010°05'E, ODMCS operating normally, no alarm recorded. Signed by Chief Engineer."

## Real Cases

Tampering with the OWS or installing bypass piping ("magic pipe") is among the most heavily prosecuted environmental violations worldwide, with criminal convictions for Masters and Chief Engineers, alongside very substantial fines for the owner.

## Common Mistakes Mistake Library

Mistake | Consequence | How to avoid it
--- | --- | ---
Manual bypass of the alarm system | Environmental offence, detention, criminal proceedings | No exceptions: in case of a fault, stop the discharge and repair the OWS
OWS never calibrated or tested | PSC deficiency, out-of-spec discharges | Calibration and maintenance per the approved plan
Discharge position not recorded | Unable to demonstrate compliance with Special Area limits | Always record position and distance from the coast

## PSC Observations

The PSCO checks the OWS maintenance status, the presence of any suspicious flanges or piping near the system, and the consistency between declared operating hours and discharged volumes.

## Operational Tips

- Keep a preventive maintenance plan dedicated to the OWS, separate from the general engine maintenance plan.
- Never ignore an ODMCS alarm, even if it looks like a false positive.
- Document every maintenance intervention or component replacement on the OWS.

## Checklist

- OWS calibrated and certified
- No unauthorised piping or flange near the system
- ODMCS alarm log consistent with ORB entries
- Discharge position always recorded

## FAQ

What is the oil concentration limit for discharge?
15 ppm under MARPOL Annex I, with automatic shutdown of the discharge if exceeded (stricter thresholds may apply to certain ship categories).
What should be done if the OWS is faulty?
Stop the discharge, collect bilge water in dedicated tanks and repair it before resuming operations; never manually bypass the system.
🎬 Additional photos, videos and interactive diagrams for this topic will be available in a future version of the platform.

## Related Topics

Oil Record Book Sludge Management SOPEP

### Leave feedback

Help us improve the platform during the beta -- it takes thirty seconds.

How useful do you find the platform so far?
Comment (optional)
Sign me up for the newsletter
Role