Step 1: Preparations Before Entering Port and Discharging Cargo
Every successful tanker discharge begins long before the manifold hoses are connected. Preparations before entering port are a blend of technical checks, safety routines, crew coordination, and compliance with international regulations. These tasks might seem routine, but history has shown that most tanker accidents occur because of poor preparation rather than equipment failure.
Why Preparations Matter
Imagine bringing a 300,000 DWT VLCC into a busy port like Rotterdam or Singapore. Even before the first drop of oil flows ashore, the vessel is already under strict observation from port authorities, terminal operators, and classification society inspectors. A misstep—such as incorrect trim, an overlooked valve, or a faulty inert gas system—can result in:
- Costly delays (up to $50,000/day in demurrage fees for VLCCs, BIMCO 2023).
- Environmental penalties (oil mist release near terminals can trigger fines exceeding $1M, according to EMSA).
- Risk of catastrophic pollution incidents, which carry not only financial but also legal liabilities under the CLC 1969 and OPRC Convention.
1. Checks, Studies, and Investigations
Before entering port, officers must confirm several key parameters:
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Berth and terminal conditions: depth, draft limits, tidal range, and current restrictions. Terminals like Jubail (Saudi Arabia) or Ras Tanura have unique draft and manifold limitations, and ignoring these can lead to grounding or rejection.
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Draft checks: not just a reading of forward/aft drafts, but also considering hogging/sagging and seawater density variations.
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Ballast and discharge plan validation: balancing efficiency with structural safety. The Chief Officer must ensure that bending moments and shear forces remain within class-approved limits.
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Crude Oil Washing (COW) plan: preparation involves confirming permissions with the charterer and terminal, as MARPOL Annex I mandates strict adherence to COW manuals.
Story example: In 2018, a Suezmax discharging at an Italian refinery faced delays because the COW plan was not pre-approved by the terminal. What seemed like a clerical oversight resulted in 36 hours of waiting time, costing both the shipowner and charterer significantly.
2. Formulating Plans
Three plans form the backbone of pre-arrival work:
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Discharge Plan – establishes the sequence, rates, and pump groupings. Efficiency is key, but so is safety. ISGOTT stresses that rate of discharge must never exceed manifold or line pressure limits.
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Ballast Plan – essential for stability. For example, propeller immersion must stay above 55%, or propulsion risks cavitation (Lloyd’s Register, 2022).
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Crude Oil Washing (COW) Plan – aims to reduce sludge and maximise outturn. Depending on charterer’s requirements, one-fourth of tanks are often designated for washing.
Analogy: Think of these plans as the “flight plan” of a cargo aircraft: they don’t guarantee a turbulence-free journey, but without them, the crew flies blind.
3. Shipboard Meetings
Meetings embody the ISM Code’s principle of safety culture. The Chief Officer explains the discharge sequence, Chief Engineer advises on pump readiness, and deck officers are briefed on valve line-ups. Such briefings prevent confusion during high-stress operations when even a single wrong valve opening can cause cross-contamination.
4. Preparations for Entering Port
Preparations include:
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Tank pressure control (to avoid gas release near populated ports).
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Ullage checks (using closed gauging systems like MMC).
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Testing communication equipment (VHF, intrinsically safe radios).
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Scupper plug verification (some Japanese ports require them cement-sealed).
Human story: A cadet once shared in a Nautical Institute forum that during his first discharge operation in Korea, his nervousness led him to forget testing the transceiver batteries. Midway through, communications failed between manifold and CCR, leading to a tense but avoidable delay.
5. Reporting
Charterers and port authorities require extensive reporting:
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Safety inspection results.
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COW plans.
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Cargo plans and ullage reports.
Failure to file these can halt operations—reminding us that discharge is as much about paperwork as pumps.
6. Work Before and After Entering Port
Tasks include:
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Tank pressure adjustments (keeping below 2 kPa before entry).
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Preparations for starting Inert Gas System (IGS) and scrubber pumps.
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Ullage and manifold pressure monitoring.
These actions ensure that once the vessel berths, cargo discharge can begin without unsafe delays.
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Step 2: Starting the Discharging Operation
The moment a tanker begins to discharge is often described by experienced Chief Officers as “the point of no return.” Once cargo begins to flow, every second counts, and errors multiply quickly if not contained. This is why the start-up phase is governed by meticulous checks, redundant safety measures, and continuous coordination with both ship and shore teams.
The Rule of “Zero Start”
One of the golden rules of tanker discharge, emphasized in ISGOTT and most tanker manuals, is Zero Start. In practice, this means that all valves must be closed—except for the Inert Gas (IG) branch valves—before the discharge sequence begins.
Why? Because an open valve left unchecked can:
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Cause accidental overflow into the wrong tank.
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Lead to cargo contamination (mixing grades of oil).
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Trigger dangerous pressure surges in pipelines.
Example: In 2016, a tanker in the Mediterranean accidentally discharged diesel into a crude tank because a line valve was not properly shut. The contamination forced the entire batch to be downgraded, costing the charterer millions. That “simple oversight” illustrates why zero start is non-negotiable.
Inspections and Checks Before Pumping
Before the cargo pump can even be touched, officers perform:
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Ullage and pressure measurements: confirm cargo quantity and tank condition.
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Valve position checks: verified against the mimic diagram in the CCR (Cargo Control Room).
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Communication tests: ensuring manifold and CCR are linked via intrinsically safe radios.
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Emergency readiness: portable detectors (HC, O₂, H₂S) and fire extinguishing equipment tested.
These aren’t just “tick-box” drills. A survey of tanker incidents by the UK Marine Accident Investigation Branch (MAIB, 2020) found that over 60% of near-miss discharges involved “communication gaps” or “valve line-up mistakes.”
Preparing the Cargo Pump
The cargo pump is the heart of the operation, and like a heart, it requires priming before use. Priming ensures no air pockets exist in suction lines, which could otherwise cause cavitation—a destructive phenomenon where vapor bubbles collapse violently inside the pump.
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Preventing water hammer: Valves are opened gradually, never abruptly, to avoid shock waves that can damage piping.
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Monitoring suction/discharge pressure: Engineers and deck officers coordinate readings in real-time.
Analogy: Starting a tanker pump without proper priming is like revving a car engine without oil—it might run briefly, but catastrophic damage is inevitable.
Starting the Pump
With checks complete, the Chief Officer authorises the Engine Room (usually one hour in advance) to start the pump. As it begins, the watch officer:
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Confirms stable RPM and pressure.
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Listens for abnormal noises (squealing, rattling = cavitation or bearing failure).
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Monitors vibration sensors if fitted.
Some modern VLCCs are now equipped with digital pump monitoring systems, which use vibration and flow sensors to predict failures. DNV reports (2023) suggest that predictive maintenance could cut pump-related delays by up to 40% in the coming decade.
Gas Purging of Lines
Before crude can flow ashore, lines must be purged of trapped gases. Using cargo oil itself, the crew circulates liquid through discharge lines to push out vapors. If gases are not purged, floating submarine pipelines at sea berths may rise dangerously, risking rupture.
At certain terminals (e.g., offshore Fujairah anchorage), purging is mandatory before hose connection. Failure to purge has, in past cases, led to visible gas blow-outs at manifolds—events that cause immediate suspension by terminal operators.
Coordination with Shore
The ship–shore safety checklist (SSSCL), endorsed by both ICS and OCIMF, must be signed jointly by Master and terminal representative before discharge begins. This document confirms:
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Emergency shutdown procedures.
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Agreed maximum pressure and flow rate.
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Communication protocols.
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Manning levels and responsibilities.
No cargo flows until both sides confirm readiness. This collaborative process reinforces that tanker discharge is not a ship-only task—it is a shared responsibility.
Human Factor in Start-Up
Despite automation, start-up remains human-intensive. The Chief Officer, Cargo Control Room operator, pumpman, and manifold watch must all act in synchrony. Training under STCW Convention and IMO Model Course 2.07 emphasizes “situational awareness” during this stage.
Cadet’s Perspective: One cadet described his first start-up watch in Fujairah as “standing at the manifold with butterflies in my stomach.” But when he saw how every valve movement was double-checked aloud—“Valve 3 closed?” “Confirmed, Valve 3 closed”—he realised that tanker discharge is not about individual skill, but collective discipline.
Risks at Start-Up
Key hazards at this stage include:
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Over-pressurisation of manifolds.
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Cargo line rupture due to surge pressures.
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Accidental mixing of grades during valve misalignment.
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Gas blowbacks if inert gas supply isn’t properly established.
According to OCIMF (2022), start-up accounts for over 30% of reported tanker discharge near-misses. This explains why the early hours of discharge require extra vigilance.
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Step 3: The Ballasting Plan – Balancing Safety, Stability, and Compliance
If cargo discharge is the “arterial flow” of a tanker, then ballasting is its “skeletal adjustment.” A tanker cannot simply pump cargo ashore without carefully adjusting its ballast water. Ballast is what keeps the ship stable, prevents structural stress, and ensures safe propulsion even when tanks are empty.
Why Ballasting Matters During Discharge
The IMO Ballast Water Management (BWM) Convention is often discussed in the context of invasive species, but ballasting during cargo operations is about something more immediate: the ship’s hydrostatics.
When tanks empty rapidly:
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Trim and heel change, affecting manifold height and hose strain.
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Propeller immersion reduces, compromising maneuverability.
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Hull stresses (bending moment, shear forces) can exceed class limits.
In fact, a VLCC (Very Large Crude Carrier) discharging in Fujairah in 2021 nearly lost propulsion during final stripping because propeller immersion dropped below 50%. The issue wasn’t mechanical — it was an inadequate ballasting plan.
The Importance of Draft
Ballast ensures that even during near-empty conditions, the vessel maintains a safe draft. Shipbuilders provide minimum operating drafts for ballast voyages.
Example – Takasago Maru (as cited in manuals):
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Ballast condition aft draft: Ensure ≥ 55% propeller immersion (~10.57 m).
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Rough sea forward draft: ≥ 7.8 m to avoid slamming.
These aren’t just numbers — they are survival margins. A tanker with insufficient draft in heavy weather risks pounding, rudder loss, or structural fatigue.
Precautions in Ballasting Plans
When formulating a ballasting plan, several factors must be weighed:
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Terminal Restrictions
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Some ports prohibit de-ballasting from After Peak Tank (APT), even when segregated from cargo.
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Others enforce zero discharge within port areas to protect oil fences.
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Pollution Prevention
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In single-hull ships (still operating in some regions despite phase-out), ballast lines often run through cargo tanks. Even a tiny leak can discharge oily water into the sea.
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MARPOL requires strict monitoring of ballast discharge. In practice, watchkeepers must check sea chest areas visually during operations.
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Hydrostatic Tests
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Conducted to detect leaks, especially where ballast lines cross cargo tanks.
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If the ballast line is damaged, it’s safer for any leakage to drain into an empty cargo tank (containing oily residues) rather than into the sea.
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Analogy: Think of a ballasting plan as a counterweight system in an elevator. If you only focus on the “downward load” (cargo discharge) without the counterbalance, the whole system becomes unstable.
Operational Challenges: Water Hammer
A notorious hazard in ballast operations is water hammer — a sudden surge of pressure caused by trapped liquid moving violently when valves are opened or closed too quickly.
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It can rupture ballast pipes.
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Damage valves.
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Even disable pumps.
For cadets, it’s often explained like this: imagine slamming your hand on the end of a water hose while water is rushing through it — the recoil is violent and instant.
Case Example: Ballast Mishap in Northern Europe
In 2019, a tanker at a North Sea terminal accidentally over-pressurised its ballast line. A valve had been left partly shut, and when suction was applied, negative pressure caused implosion of part of the pipeline. The repair cost was minor compared to the 12-hour delay, which translated into nearly $250,000 in lost time charter value.
This case reinforced the importance of valve checks, pressure monitoring, and communication between deck and engine departments.
Ballasting and Environmental Compliance
While operational safety drives the ballasting plan, environmental compliance is equally critical.
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The BWM Convention (2017 enforcement) mandates treatment or exchange of ballast water to prevent invasive species transfer.
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Some coastal states (e.g., Australia, Canada) enforce stricter ballast reporting, with penalties for even small infractions.
For officers, this means that a ballasting plan must not only satisfy stability and strength calculations, but also align with international and port-state regulations.
Crew Training and Human Factor
Ballast operations are often supervised by junior officers, but oversight by the Chief Officer is crucial. STCW training requires cadets to understand:
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Draft readings and corrections.
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Pump suction/discharge monitoring.
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The relationship between ballast operations and hull girder strength.
In simulator training (e.g., Wärtsilä TechSim, Kongsberg), cadets practice scenarios like ballast pump failure during discharge, teaching them to balance remaining pumps while protecting hull integrity.
Ballasting as a Parallel Operation
One of the biggest challenges is that ballasting happens simultaneously with cargo discharge. This increases workload and risk of error. The crew must:
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Maintain situational awareness.
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Coordinate line-ups to avoid cross-contamination.
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Ensure no de-ballasting into restricted areas.
OCIMF’s guidance stresses that parallel operations increase risk, which is why many companies implement the “two-man rule” — at least two officers must be present when switching ballast valves during discharge.
Key Takeaways for Cadets and Officers
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Ballasting is not secondary — it is a critical safety operation.
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Minimum drafts and propeller immersion rules must always be respected.
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Avoid water hammer by slow valve operations.
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Pollution risks are higher in ballast operations than most cadets realise.
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Coordination with cargo discharge is key to safe tanker operations.
Step 4: Crude Oil Washing (COW) – Maximising Outturn, Minimising Pollution
For many decades, oil tankers carried not only cargo but also a hidden environmental burden: huge quantities of residual oil (sludge and clingage) left inside tanks after discharge. Before the 1980s, these residues were often washed out with seawater, resulting in chronic oil pollution. The scale was staggering — according to IMO estimates, over 1 million tonnes of oil per year were discharged into the oceans through tank washing prior to MARPOL Annex I enforcement.
The solution was Crude Oil Washing (COW): using the cargo itself, under pressure, to clean tanks during discharge. Today, COW is mandatory under MARPOL Annex I Regulation 33 for all new crude oil tankers above 20,000 DWT, and optional but recommended for smaller vessels.
Why COW Matters
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Environmental Protection
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Prevents oil-contaminated seawater discharges.
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A significant contributor to MARPOL’s success: global oil pollution from ships has dropped by ~90% since the 1970s (IMO, 2023).
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Commercial Benefit
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Reduces “ROB” (Remaining On Board) cargo.
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More cargo delivered = higher revenue.
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A well-executed COW operation can free up hundreds of tonnes of recoverable oil in a VLCC, representing millions of dollars annually across fleets.
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Operational Efficiency
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Minimises sludge buildup, easing future tank cleaning and dry-dock maintenance.
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Slows corrosion inside tanks by reducing moisture retention.
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Advantages vs. Disadvantages
Advantages:
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Additional cargo capacity (cleaner tanks = more space).
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Prevents mixing/degradation of oil grades.
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Reduced sea pollution.
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Tanks remain cleaner for inspections.
Disadvantages:
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Increases workload — conducted simultaneously with discharge and ballasting.
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May extend total discharge time.
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Vapor losses and static electricity risks require careful control.
The COW Process
COW uses high-pressure jets of cargo oil (typically 0.8–1.0 MPa) directed through fixed tank washing machines.
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Top wash – loosens sludge from upper structures.
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Bottom wash – flushes deposits toward suction bellmouths.
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Stripping – ensures loosened residues are pumped ashore.
On double-hull tankers, simpler tank geometry makes single-step washing effective. Older single-hull tankers sometimes require multi-step washing for thorough results.
Safety Precautions
MARPOL and ISGOTT stress that COW is only safe when strict procedures are followed:
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Inert Gas System (IGS) must be operational:
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Oxygen concentration < 8% by volume before washing starts.
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Tank pressure maintained between +2 and +10 kPa to prevent air ingress.
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No high vapor pressure cargoes (>0.05 MPa Reid Vapor Pressure) should be washed, unless terminal authorises limited bottom washing.
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Static electricity control: washing oil supply tanks must be topped >1 m to prevent vortex and moisture entrainment.
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Trim requirements: typically ≥4 m trim by stern during bottom washing to maximise effectiveness.
Sludge Control
Charterers often require that at least one-fourth of cargo tanks are washed on each voyage for sludge management.
Rules also state:
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Same tank should not be washed more than twice in four months.
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All COW must be completed before departure from final discharge port.
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No COW during ballast passage.
This ensures regular but controlled sludge management without excessive workload.
Case Example: COW Delay in Qatar
A VLCC discharging Qatar Marine crude in 2022 was instructed by the terminal to suspend washing after oxygen readings exceeded 8%. The crew had overlooked a minor IG fan fluctuation. Result: 9 hours of downtime, and charterers issued a Letter of Protest. Lesson learned: IG monitoring must be continuous, not intermittent.
Tanker Crew Training in COW
STCW and IMO Model Course 2.07 require cadets and officers to:
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Interpret the Crude Oil Washing Operations and Equipment Manual (COW Manual).
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Conduct oxygen testing before tank entry/washing.
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Operate washing machines in line with safety restrictions.
Many academies now use simulators to replicate COW, teaching cadets how small misjudgments (like wrong trim or valve misalignment) can compromise efficiency and safety.
Technological Developments
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Automated COW monitoring systems: linking washing pressure, oxygen levels, and pump discharge to digital consoles.
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Class requirements: Some societies (e.g., LR, ABS) now encourage integrated sludge monitoring sensors.
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Environmental performance: Recent studies (DNV, 2022) show automated washing can reduce sludge residues by 20–25% compared to manual methods.
Human Element
For many junior officers, COW is one of the most stressful duties. Unlike straightforward pumping, it involves three simultaneous operations: discharge, ballasting, and washing. This demands multi-tasking under pressure, but also reinforces why teamwork is the backbone of tanker operations.
As one senior Chief Officer told cadets during training:
“Discharging is science, ballasting is balance, but COW is art. You need patience, timing, and respect for the ship.”
Key Takeaways
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COW is mandatory on crude tankers >20,000 DWT.
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Must comply with MARPOL, COW Manual, and terminal restrictions.
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Oxygen <8% and tank pressure >2 kPa are absolute safety limits.
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Done properly, COW boosts commercial returns and environmental compliance.
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Done poorly, it risks safety, delays, and pollution.
Step 5: Shipboard Meetings – Building the Safety Net of Communication
If the discharging plan is the blueprint, then shipboard meetings are the glue that binds crew actions together. Oil tankers are vast, complex machines, but it is people — officers, engineers, ratings, and shore staff — who must execute every valve turn and pump start. Coordination failures are among the top three causes of tanker incidents (OCIMF, 2021). That is why structured pre-discharge meetings are mandatory under ISM Code safety culture principles and emphasised in ISGOTT checklists.
Why Meetings Matter
Cargo operations are high-stakes, and no officer should assume “everyone knows their role.” Tanker discharges involve parallel operations (ballasting, crude oil washing, pump running), where a single miscommunication can cause:
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Cargo contamination (wrong tank discharged or cross-connected).
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Valve misalignment leading to overflow.
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Delayed emergency response if alarms are misinterpreted.
Example: In 2017, a tanker in Singapore discharged jet fuel into a diesel tank because valve line-up was misunderstood between deck and CCR staff. Though contained, the incident caused $2.5M in cargo loss and triggered severe terminal penalties. A post-incident investigation showed the shipboard pre-discharge meeting had been rushed.
The Structure of Shipboard Meetings
Before arrival, the Chief Officer (cargo operations lead) convenes the meeting, usually in the cargo control room (CCR) or messroom. Attendees include:
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Master (overall command, approves plan).
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Chief Engineer (advises on pump readiness, machinery).
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Deck officers & pumpman (valve operation, manifold duties).
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Engine officers (pump power supply, IG system).
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Ratings (manifold watch, deck checks).
Together, they review:
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Discharge plan (sequence, pump use, terminal restrictions).
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Ballast plan (trim, heel, minimum drafts).
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Crude Oil Washing plan (tanks to wash, safety limits).
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Emergency procedures (shutdown, fire, pollution).
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Communication methods (VHF channels, hand-held radios).
The Master’s Role
The Master checks that the Chief Officer’s plan aligns with charterer/terminal instructions. He may add advice based on experience — for instance, reminding the team of local tidal currents or terminal-specific rules (some Japanese ports require scupper plugs to be cement-sealed).
Story: A retired Master once recalled that during a busy discharge at Ras Tanura, he spotted the terminal representative looking uneasy. When asked, the rep explained that a “small” difference in trim was already outside terminal limits. The Master’s proactive oversight prevented a potential shutdown.
The Chief Officer’s Role
The Chief Officer is the operation’s conductor. He:
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Explains the valve line-up and emphasises the Zero Start rule.
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Assigns stations: one officer in CCR, one on deck, pumpman at pump controls.
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Ensures cadets and junior officers know when to observe silently and when to act.
The Chief Officer also explains special procedures such as:
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Commingled loading (different grades mixed with charterer’s permission).
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Mixed loading (grades combined into a uniform blend).
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Load on Top (LOT) (loading oil onto slops after water separation).
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Shore line flushing (using ship’s pumps to flush submarine lines).
Even experienced officers benefit from reminders — because tanker operations punish assumptions.
The Chief Engineer’s Role
Though often focused on machinery, the Chief Engineer plays a critical role:
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Confirms cargo pump readiness.
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Advises on inert gas system (IGS) status.
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Ensures emergency systems (fire pumps, foam monitors) are ready.
Without engine room coordination, cargo discharge would stall. Many companies encourage bridge–engine cross-briefings before arrival, ensuring both sides share the same mental model.
Communication Protocols
Meetings standardise how crew communicate during operations. Examples:
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Valve orders: “Valve 3 open?” → “Confirmed, Valve 3 open.”
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Radio checks: conducted before berthing.
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Alarm acknowledgement: Only CCR officer acknowledges alarms; deck officers report observations.
This prevents the classic error of two people assuming the other is in control.
Cultural and Human Factors
On international tankers, crews often come from multiple nationalities. Language barriers can lead to fatal misunderstandings. That is why IMO Model Course 3.17 (Maritime English) and ISM procedures encourage closed-loop communication: repeating orders aloud until confirmed.
Cadet reflection: “During my first pre-discharge meeting, I thought it was just formal talk. But when a real valve misalignment was spotted mid-operation, I realised those instructions were the difference between routine and disaster.”
Emergency Coordination
Shipboard meetings also cover:
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Emergency shutdown triggers (high manifold pressure, IG failure, oil leak).
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Pollution response: SOPEP equipment (oil booms, absorbents) positioned near manifolds.
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Fire scenarios: Fire teams and extinguishers tested at manifold.
Such rehearsals may feel repetitive, but they build muscle memory. As one P&I Club report notes (UK P&I, 2020), drills reduced real response time by over 50% in tanker incidents.
Lessons from Past Incidents
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Prestige (2002): Though structural, the disaster showed the importance of transparent communication between Master, owners, and authorities.
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Exxon Valdez (1989): Crew fatigue and lack of briefings contributed to navigational failure, highlighting that safety culture is as vital as technology.
Key Takeaways
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Shipboard meetings are non-negotiable under ISM and ISGOTT.
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They bridge the gap between plans on paper and crew actions in real time.
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Masters and Chief Officers must model clear communication.
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Meetings reduce accidents, delays, and financial losses.
Step 6: Preparatory Work Before and During Cargo Discharge
If cargo discharge were a stage performance, then the preparatory work is the unseen rehearsal — the fine-tuning that ensures the actual operation runs smoothly, safely, and without interruption. Tanker checklists at this stage might look repetitive, but they exist because every accident ever studied had one thing in common: someone skipped a check.
From testing manifold gauges to verifying valve line-ups, these preparations are designed to anticipate the unexpected.
Checklists – The Backbone of Readiness
Modern tankers follow SMS (Safety Management System) checklists aligned with ISGOTT. These are not bureaucratic paperwork but practical risk controls.
Typical pre-discharge checks include:
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Manifold pressure gauges – ensuring they read correctly both inboard and outboard. Damaged gauge threads can leak, creating both a spill and fire hazard.
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Inert Gas main pressure vs. P/V breaker settings – confirming tank pressures align with safe operating margins.
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Communication systems – testing radios and transceivers to ensure clear CCR–manifold contact.
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Portable detectors – O₂, HC, and H₂S meters must be tested and charged, as cargo vapors can incapacitate crew within seconds.
Case study: In 2020, a North Sea tanker was delayed when a portable H₂S meter failed calibration just before cargo transfer. No terminal will allow discharge without working detectors — a small oversight that resulted in 14 hours of costly waiting time.
Lighting and Emergency Systems
Before operations:
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Deck and pump room lights are checked for full illumination.
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Emergency hydraulic hand pumps are tested — training cadets often get hands-on experience here, learning that the simplest manual tools may be the only safeguard in a blackout.
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Fire extinguishers (often CO₂ with hoses at the vent riser) are placed ready for instant use, since vent fires can ignite during gas release.
Training exercises often include mock vent fires, teaching crew to react under pressure. As one pumpman noted in an ISWAN interview:
“The fire we fear most is not in the engine room — it’s the invisible one at the vent riser during cargo handling.”
Pollution Prevention Readiness
Oil spills, even a few liters, trigger SOPEP (Shipboard Oil Pollution Emergency Plan) protocols and terminal shutdowns. To prevent this:
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Scupper plugs are inspected. Some Japanese terminals require them cement-sealed, not just fitted.
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Oil spill kits (booms, absorbents, dispersant sprayers) are staged near manifolds.
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Line proportioners (for treating minor spills) are checked for crew familiarity.
Example: In 2019, a tanker in South Korea was fined heavily after a minor spill at the manifold revealed the crew had improperly fitted scupper plugs. The oil fence deployed by the terminal contained the leak, but the crew’s lack of preparation caused reputational damage.
Valve Position Checks – The Art of Line-Up
Valve positions determine whether cargo flows smoothly or chaos unfolds. Correct line-up requires:
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Hydraulic valve checks against CCR mimic diagrams.
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Manual valve inspection on deck.
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Double verification (orders given aloud and repeated back).
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Pumpman’s signature on the checklist, with Chief Officer’s countersignature.
This ensures accountability. The ISM Code promotes the “two-man rule”, reducing the risk of one tired officer making a costly error.
Anti-Freezing Measures in Cold Regions
Tankers trading in the Baltic, Arctic, or North Pacific face unique challenges. Cold weather can freeze lines, making valves inoperable. Preparations include:
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Adjusting P/V breaker seal water with antifreeze solutions.
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Draining slop tank heating lines and inert gas drains to prevent ice blockages.
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Checking deck water seals (often steam-heated) for proper function.
Neglecting these steps can cripple cargo operations mid-transfer. In one reported AMSA case (2017), a tanker in northern China was forced to suspend discharge for 36 hours due to frozen IG lines.
Tank Pressure Control
Cargo tanks behave like giant lungs — expanding and contracting with temperature. Before entering port, some terminals demand that tank pressure be reduced to ~2 kPa to prevent unwanted gas release at berth.
During discharge:
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Pressure rises due to ambient heat.
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Sea water sprays may be used on deck to keep tanks cool.
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Vent riser valves must be operated gradually to avoid pressure surges.
Odors are also treated as pollution in many modern ports. Residents near Rotterdam or Houston have successfully lobbied for tighter controls on hydrocarbon smells, meaning a mismanaged vent is not only unsafe but also a breach of air quality regulations.
Inert Gas System (IGS) Preparations
The IGS is the tanker’s shield against explosions. Before cargo flow starts:
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Scrubber pump is started early (to avoid soot discharge at berth).
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IG oxygen concentration is confirmed below 5% vol.
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Deck seal and deck water systems are checked.
Cargo cannot legally be discharged until tanks are inerted. IMO requires IGS supply capacity to exceed 1.25 times the maximum discharge rate.
Terminals frequently ask for live O₂ readings before authorising pump start.
Ullage Measurement Precautions
Some ports require ullage checks before berthing. Risks include:
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Exposure to toxic H₂S (especially with Middle Eastern crudes like Qatar Land).
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Deck workers are instructed to stand perpendicular to the wind and use closed gauging devices whenever possible.
Fatalities have occurred when workers inhaled concentrated vapors during open ullaging — making training and protective gear critical.
Reports and Documentation
Before operations commence, the following are typically sent to charterer, agent, and authorities:
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Safety inspection results.
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Discharge plan.
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Crude Oil Washing plan.
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Cargo plan with ullage figures.
Without these, terminals may refuse to connect hoses. This demonstrates how paperwork is as operationally critical as pump pressure.
Human Factor – The Final Check
No matter how advanced the tanker, the final safeguard is always crew awareness.
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The Chief Officer personally checks IG branch valves and tank pressures.
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The Master ensures reports are filed.
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Junior officers double-check line-ups under supervision.
As ISGOTT reminds, “No ship is safer than the discipline of her crew.”
Key Takeaways
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Preparatory work is the “hidden engine” of safe cargo operations.
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Checklists, detectors, and valve line-ups prevent catastrophic mistakes.
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Pollution prevention tools must always be staged and crew trained.
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Cold-weather and tank pressure controls show how environmental factors directly shape discharge safety.
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IGS readiness and ullage precautions are not optional but legal requirements.