Answer
Yes, absolutely.
Under MARPOL and Classification Society rules, you cannot arbitrarily "re-designate" a tank's statutory status on your own, but you can use an alternative tank for temporary storage/retention to prevent a machinery space flood.
1. The "Safe" Tanks You Can Use (Inside the Engine Room)
Your best choices are tanks already listed under Section 3.1 of your ship’s IOPP Certificate Form A or B (Tanks for Bilge Water or Oily Residues).
Oily Bilge Settling / Primary Holding Tanks: Your immediate fallback.
Dirty Oil Tank / Used Lub Oil Tank: Acceptable for temporary storage. Since these tanks hold oily waste meant for the incinerator or shore discharge, mixing bilge water into them does not create a new category of pollution risk.
The Sludge Tank Trap ⚠️ (Crucial for Orals)
The examiner might ask: "Can you pump bilge water into the Sludge Tank?"
Your Answer: "Technically yes, in an extreme emergency to save the engine room, but it is highly restricted and avoided."
The Reason: Under MARPOL Annex I, Regulation 12, sludge tanks are strictly intended for oily residues (from purifiers/filters). Since the 2017 amendments (Resolution MEPC.266(68)), sludge tanks must have no direct piping connections to the bilge system or the OWS to prevent operators from bypassing the OWS.
How to handle it: If you must use it, you will likely have to use a temporary portable pump (like a Wilden/diaphragm pump) to transfer the water over the top manhole, or use the standard settling drains. Note that putting water into a sludge tank ruins its homogeneity, making it very difficult to incinerate later.
2. Can You Use an Empty Fuel Oil Tank or Ballast Tank?
This is a High-Risk/Emergency-Only action.
Fuel Oil Tank: Never done under normal operations. If you pump water into a fuel tank, you contaminate the fuel system, risk damaging main propulsion machinery, and create massive volumes of off-spec fuel.
Ballast Tank: Strictly Forbidden under normal circumstances. Pumping oily bilge water into a dedicated ballast tank turns that clean tank into an illegal "slop tank." You would then be unable to discharge that ballast water without routing it through an Oil Discharge Monitoring Equipment (ODME) or pumping it to shore, violating your international ballast water management certificates.
3. The 3 Steps to Legally Execute and Document the Transfer
If your bilge holding tank is full, the OWS is broken, and you are transferring bilge water to an alternate internal tank to prevent flooding, you must follow this strict regulatory protocol:
Step 1: Obtain Authorization
Before making any non-standard internal transfers, formally notify the Master. Ensure the risk assessment is updated within the ship's Safety Management System (SMS).
Step 2: Use the Right Pump
Because permanent pipe connections between clean/fuel tanks and the bilge lines do not exist (to prevent accidental pollution), you will typically have to rig a portable pneumatic diaphragm pump (Wilden pump) to transfer the liquid safely.
Step 3: Precise Logging in the Oil Record Book (ORB) Part I
If you do not log this correctly, Port State Control (PSC) will flag it as an illegal modification or an unrecorded bilge transfer, which carries severe criminal penalties under the Indian Merchant Shipping Act, 2025.
You must log the entry under Code D (Non-automatic discharge overboard or disposal otherwise of bilge water):
Code: D
Item No: 15.3 -> Transfer to slop tank or holding tank (Identify the temporary tank used)
Item No: 15.4 -> State quantity retained in the tank in cubic meters (m³)
Oral Closing Statement: "Sir, in an emergency, I will use internal resource management to transfer bilge water to an available dirty oil tank or a designated holding tank using a portable pump. I will ensure no cross-contamination occurs with ballast or clean systems, and I will explicitly log the tank-to-tank transfer under Code D of the Oil Record Book Part I to maintain complete regulatory transparency."