Overall, compliance with IMO DCS requires accuracy of all data reported. In particular, the final report that each Company will provide to Flag Administrations for each of its managed vessels should include the exact quantity of consumed fuel onboard. The most commonly made mistakes and gaps in these measurements usually arise during bunkering operations; as a result, the figures that a vessel will report may not be correct if the quantities measured and included in the BDN are not accurate. Thus, a proper bunkering procedure can provide correct and accurate results for data collection.

Methods for measuring ship emissions

Namely, the IMO DCS circular (included in Res. MEPC.282(70) as adopted on 28 October 2016) has defined three methods for the measurement of emissions consumption on board:

  1. Bunker Delivery Note (BDN)
  2. Flowmeters
  3. Fuel oil tank monitoring on board


All the above methods involve the bunkering operation either as primary procedure (BDN) or secondary (verification or calculation procedures- Flowmeters, Fuel Oil Tank measurement).

Calculating annual consumption

The first method is based on the assumption that annual fuel oil consumption would be calculated as the total mass of fuel oil used on board the vessel as reflected in the BDNs. In this method, the BDN fuel oil quantities would be used to determine the annual total mass of fuel oil consumed, plus the amount of fuel oil left over from the last calendar year period and less the amount of fuel oil carried over to the next calendar year period. Fuel retransferred or spilled for any reason during reported period should also be subtracted.

In other words, the annual consumption is calculated as:

Annual consumption = the fuel in tanks at the beginning of measuring period + fuel bunkered (through BDNs) - the fuel in tanks at the end of measuring - the fuel retransferred or spilled

BDN : Key elements & focus areas

The revised MARPOL Annex VI involves bunker suppliers to the procedure and therefore the bunkering delivery note should include a declaration signed and certified by the fuel oil supplier's representative that the fuel oil supplied is in conformity with regulation 18.3 of MARPOL Annex VI and that the sulfur content of the fuel oil supplied does not exceed:

  1. the limit outside emission control areas under regulation 14.1;
  2. or the limit in ECAs under regulation 14.4;
  3. or the purchaser's specified limit value, on the basis of the purchaser's notification that the fuel oil is intended to be used in combination with an equivalent means of compliance or is subject to a relevant exemption for a ship to conduct trials for sulfur oxides emission reduction and control technology research.

The accuracy of BDN is essential for the proper implementation of IMO DCS (even if the Method 1 Using BDNs is not used). The typical data provided in the BDN is:

  1. Name and IMO number of receiving ship
  2. Port of Bunkering
  3. Date of commencement of delivery
  4. Name, address, and telephone number of marine fuel oil supplier
  5. Delivered Product (s) name
  6. Quantity (metric tons)
  7. Density at 15o C (kg/m3)
  8. Sulphur content (% m/m)
  9. A declaration signed and certified by the fuel oil supplier’s representative that the fuel oil supplier is in conformity with the applicable MARPOL regulations.

Tips for an effective bunkering procedure

Considering that accuracy in calculations is vital for IMO DCS compliance, any quantity dispute should be addressed properly. In this regard, it is necessary to establish a detailed and effective bunkering procedure which should be monitored and performed by competent and trained personnel.

  1. Provisions in the procedure should include quantities measurement prior, during and after bunkering. The BDN will indicate a quantity figure for bunkered fuel (all different types of bunkered fuel, separately) and officer in charge (usually Chief Engineer or Chief Officer) is the responsible officer to accept or not.
  2. Responsible officer should be very careful and follow the established bunkering plan which has pre calculate the quantities to be bunkered and transferred to each applicable tank.
  3. To avoid measurement inaccuracies (or different fuel contamination), any provision should be taken in order to load bunkered fuel to the empty, recently-cleaned tanks.
  4. In case of quantity dispute, a pre-formatted Note of Protest (or similar titled document) should be issued and forwarded to head office.  The main parts of such a note should be the vessel’s officer responsible (who issues and signs the note), vessel’s name and IMO, the bunkering date, the quantity missing from total and when total quantity requested. Details of Bunkering Company should also be included (barge name, Company etc). Every effort is to be made in order the note to be signed by bunkering company’s representative.