Failed 15 ppm alarm and pressure to bypass the oily water separator
A 9,000 GT bulk carrier is 12 nautical miles from port with 12 m³ of oily bilge water in an 18 m³ holding tank. The oily water separator is rated at 5 m³/h and has a 15 ppm bilge alarm. During a trial discharge at 2 m³/h, the alarm sounds after 10 minutes and will not reset; the separator stops. The first engineer says the coalescer is old and proposes opening the bypass around the alarm to finish before arrival, because shore reception is expensive and the tank will otherwise be full. The oil record book shows the last overboard discharge three days ago; entries are signed by the chief engineer. Port state control is expected on arrival, and the company SMS requires retention unless discharge is legal and monitored. The chief engineer must decide what to do with the bilge water, what to record, and how to troubleshoot without violating MARPOL.
1. What should the chief engineer do immediately, and why is the proposed bypass unacceptable?
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Stop the trial discharge and secure the OWS. Do not open the bypass; a bypass around the 15 ppm alarm is a deliberate MARPOL violation and would be indefensible in a PSC inspection. Retain the 12 m³ in the holding tank, inform the master and company, and arrange shore reception at the next port. If tank capacity is tight, reduce other bilge inputs, repair the OWS, and consider transferring to a dedicated retained bilge tank if the SMS permits. The legal position: oily bilge water may be discharged only through the OWS with the 15 ppm alarm working and while the ship is proceeding, outside special areas where applicable. If the equipment is defective, the discharge is not legal. The chief engineer must not sign an ORB entry for a discharge that did not take place or was not properly monitored. Immediate records: note the failed trial, alarm, OWS condition and retention in the engine room log; prepare the ORB and shore receipt for the retained water.
2. How would you troubleshoot the separator and decide whether it can be used before arrival?
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Troubleshoot as a maintenance problem, not a discharge problem:
- Check the separator/coalescer element condition, prefilter and pump. A 10-minute run before the alarm suggests the element is saturated or the oil content meter is seeing carry-over.
- Backflush or renew the coalescer; clean the separator bowl if fitted; check the alarm sample line for blockage or air.
- Verify the 15 ppm monitor with the manufacturer’s test method or a known sample; a faulty sensor can cause false alarms, but do not assume that without proof.
- Check the feed rate; 2 m³/h may be too high for the condition of the element or the emulsion.
- After repair, test with clean water and then with a controlled oily sample if the procedure allows; confirm the alarm operates and the discharge is clear. If the OWS cannot be restored before arrival, retain the water and discharge ashore. A repaired and tested OWS is the only basis for resuming overboard discharge.
3. What records and evidence would you prepare for port state control, and what principles guide your entries?
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For PSC and records:
- Present the ORB, engine room log, maintenance records and the shore reception receipt. Be transparent about the failed OWS trial; a truthful record is far better than a false one.
- Confirm ORB entries are complete, signed and consistent with tank soundings. Do not create back-dated entries.
- Show that the OWS alarm and shutdown were tested and that the bypass is sealed or blanked if required.
- If a defect is found, record the corrective action and retain evidence of repair.
- Brief the crew that the bypass is not an option; the cost of shore reception is not a legal defence. The judgement is that the chief engineer’s duty is to protect the sea and the ship’s legal position, not to save a small disposal cost.