Ship bunkering is the act of supplying fuel to ships, sometimes called bunker fuel. It involves transferring fuel oil into a ship’s tanks from a storage facility, which could be any one of an ocean going vessel, tanker truck, or land based storage tank.
Why is Ship Refuelling Called Bunkering?
The term “bunkering” originates from the word “bunker”, which originally referred to the containers used to store coal on steamships. However, these days, it usually refers to types of marine fuel oil.
Bunkering doesn’t only describe the loading of fuel onto a ship, it also covers all the related operations including: measurement, transfer, sampling, recording quantities, and ensuring safety and environmental compliance.
How is Bunkering Calculated (Amount of Fuel)?
1. Calculate Total Fuel Needed for the Voyage
Ship fuel is consumed by several key areas and all must be accounted for:
a. Main Engine Consumption
The main engine(s) will consume the most fuel during the voyage. The below equation shows how this is calculated at a basic level:
Main Engine Consumption = Specific Fuel Consumption (SFC) × Engine Power (kW) × Voyage Time (hrs)
b. Auxiliary Engine Consumption
Auxiliary engines are used to power onboard generators, usually used for electrical power and lighting:
Aux Consumption = Number of Generators × Average Load (kW) × SFC × Time
2. Add Safety Margins
Not every voyage is the same, even if the planned route is. In many cases a ship will need to navigate around bad weather to avoid exposing it to potential disaster. This cannot be foreseen accurately so estimates for delays and diversions are used, normally by analysing route and time of year.
For example, if travelling through the doldrums (within 5 degrees of equator) you can expect calm weather for the most part but can also encounter wild storms. Alternatively if sailing South of latitude 60 then you can expect heavy resistance from wind and waves (also known as the roaring 60s).
Other minor consumption factors may include delays at port or sea and unforeseen equipment inefficiencies.
However, if the safety margin is too great then the ship ends up carrying unnecessary fuel which requires still more fuel to move the extra weight. Thus the chief engineer must balance these factors – whilst still ensuring they do not run out of fuel at sea.
As a rule of thumb, a chief engineer will typically add 10 – 15% as a safety margin.
Bunkering Safety Margin = (Main Engine Consumption + Aux Consumption) * 0.15
3. Subtract Onboard Fuel (Remaining On Board – ROB)
The crew will use tank soundings (with sounding tape or tank gauges) to measure how much fuel is already onboard and subtract it from the total required:
Bunkering Required = Total Voyage Fuel (steps 1 & 2) − Fuel Already Onboard (ROB)
4. Convert Volume to Weight (or Vice Versa)
Unlike your car, which measures fuel in relatively small units such as litres, ships use a lot of fuel so it is measured by weight or larger volume units such as m³:
- Weight (metric tons, MT) for purchase and usage tracking
- Volume (m³) for tank levels
If converting from one to the other then the fuel density (kg/m³) is required, which changes with ambient temperature. It is normally estimated at an ambient temperature of 15°C. To convert from mass to volume the formula is:
Volume (m³) = Density (kg/m³) / Mass (kg)
Or to convert from volume to mass:
Mass (kg) = Volume (m³) × Density (kg/m³)
5. Check Tank Capacity & Confirm Segregation
This point may sound obvious but the engineer must ensure they have adequate storage capacity for the bunker fuel and that different fuel grades are not mixed. Part of his checklist includes:
- Total fuel to be received fits in the available tanks
- Different grades (e.g., HFO, MGO) are stored separately
- Maximum filling limits are adhered to (usually 90% to allow for expansion)
Types of Bunkering Operations
Bunkering can be executed either in port via land based tankage or whilst anchored at sea. The processes are typically similar, with the only differences being to account for variation in storage platform. Some typical examples are:
Ship-to-ship bunkering (STS): Fuel is delivered from one ship (often a fuel barge) directly to another ship at sea or at anchor.
Stern line bunkering (SLB): Fuel is delivered via a stern pipe from one ship directly to the other ship with both anchored at least 100m apart. This is safe during calm seas but becomes risky during inclement weather when ships may be pitching or rolling.
Truck-to-ship: Fuel trucks travel to and supply ships docked in port.
Terminal-to-ship: Ships are refuelled directly from storage tanks whilst in port.
Ship to Ship Bunkering Procedure
Bunkering typically follows the following order of operations:
- Specification of the fuel grade and amount by the chief engineer conforming to ISO Regulation 8217
- Confirmation and agreement of the above by the ships master
- Ordering of the fuel from specialist bunkering providers, such as MH Bland
- Pre-bunkering meeting to specify crew roles, safety procedures and equipment preparation
- Awareness of the SOPEP (Ship Oil Pollution Emergency Plan) and what to do in case of spillage
- Maneuvering into position for the refuelling (including anchoring plan if ship to ship bunkering)
- Execution of tank filling
For a much more detailed run through you can also click through to this article on bunkering procedures [INTERNAL LINK].
Bunkering in Maritime Law
In many shipping contracts, such as charter agreements, cargo transport contracts, and marine insurance, there is an obligation on the shipowner or operator to ensure the vessel is seaworthy. This means the ship must be in good condition, properly staffed, and adequately bunkered (fuelled) before starting a voyage.
If the operator plans to bunker during the trip, then this must be clearly written into the applicable contract. If not then stopping to refuel could be seen as a deviation, which is a violation of the agreement. On the flip side, if a ship runs out of fuel in the middle of the ocean, that is also a major breach of contract, which could lead to insurance cancellation or claims from cargo owners. It may even result in the need for a rescue or salvage operation.
In such cases where a deviation has occurred then insurance might be voided if the ship runs into a disaster. Therefore the bunkering estimations and process must be well documented and executed flawlessly to avoid such issues.
Summary
Ship bunkering is the process of refuelling ships, involving not just transfer of the fuel but also planning, measurement, safety, and regulatory compliance.
Fuel requirements are calculated based on main and auxiliary engine consumption, safety margins, and remaining onboard fuel, with careful attention to tank capacity and segregation.
Bunkering must be properly documented in shipping and insurance contracts, as unscheduled refuelling or running out of fuel can lead to serious legal and financial consequences for the shipping company.
If you have bunkering requirements then MH Bland can provide you with information and fuel in any port you require. Please contact us to find out more.