Mandatory Fuel Oil Change Over Procedures as from 1 July 2010

According to Marpol Annex VI Regulation 14, on or after 1 July 2010 vessels should have written fuel oil change over procedures when using deferent grades of fuel oils before entering or after leaving Emission Control Areas.

Description of the Requirement

Until now written fuel oil change over procedures where not mandatory. These written procedures should be available on board before the next periodical Marpol Annex VI survey after 1 July 2010. It is recommended procedures to be available on board after 1 July 2010 in order to avoid Port State Control deficiencies in the event of an inspection.

The following should be recorded in Engine Log book:
- Volume of low sulfur fuel oils in each tank
- Date, time and postion of vessel when change over took place. (Before entering Emission Control Areas)
- Date, time and postion of vessel when change over took place. (After leaving Emission Control Areas)

While ships are operating within an Emission Control Area, the sulphur content of fuel oil used on board ships shall not exceed the following limits:
1.50% m/m prior to 1 July 2010;
1.00% m/m on and after 1 July 2010; and
0.10% m/m on and after 1 January 2015.

MEPC.176(58) circular with
all amendments of Marpol Annex VI can be downloaded.

Factor Affecting Fuel oil change over procedures

Fuel sulphur content During change-over, high-sulphur fuel is mixed with low-sulphur fuel. The time needed for the change-over is calculated on the basis of a complete linear blend. This calculation is done using our Low Sulphur Fuel Oil Change-over Calculator, included in the Plan.
Fuel consumption Higher fuel consumption means a shorter change-over period. Fuel consumption is a function of ship speed, loading level and auxiliary power requirements.
Fuel tank arrangement The configuration of fuel tanks also affects the duration of the change-over. A fuel tank arrangement which consists of one settling tank and one service tank will take longer to flush than one which consists of two settling and two service tanks. For ships with separate low and high-sulphur fuel tanks, the change-over period will be very short.
Possible Switching scenario between HFO and LSHFO with one service and one settling tank

If the ship has only one HFO service and one HFO settling tank, and assuming that it is possible to completely drain them with a transfer pump, and the operator deems it feasible to do so even at sea, the switchover procedure may include the following phases:
Switching from HFO to LFO operation
stopping the separator
perhaps draining the bottom sludge to the sludge tank
draining the HFO service and HFO settling tanks completely with the transfer pump to a storage tank with the same fuel quality
filling the settling tank with the new quality
possibly changing the gravity disc of the separator
restarting the separator
filling up the service tank via the separator (at least partly to a safe level), and
switching over to this new fuel
Depending on the ship this procedure may take perhaps 15 hours in case the service tank is filled to 50 % before taken into use.

This is an abstract from Wartsila low sulfur change over guidelines manual. The complete document can be downloaded in this

Dilution scenarios

DNV Theoretical sulfur dilution calculation table

How to use the following table

1. You have to know the sulfur content of both fuels, HFO and low sulfur fuel
2. Mark in the “Sulfur HSFO axis” the % sulfur content of your HFO
3. Move your pen upwards until you intersect the colored lines that best describe the % sulfur content of your low sulfur fuel.
4. Read the percentage value indicated at that hight in the vertical axis on the left side
And finally
5. Multiply the percentage value with the operation time you have estimated for the blended volume of fuel

The following text has been pasted from DNV guidelines.

The optimal fuel oil (FO) system for switching to LSFO is to have double service and double settling tanks, which allows LSFO to be completely segregated from HSFO from the storage to the service tank. Blending will only takes place in the piping between the service tanks and the inlet to the engine.

If the FO system contains two service tanks and two settling tanks, and the blending volume contains fuel oil for 15 minutes of operation, the dilution time according to the graph below is 240%*15 minutes = 36 minutes when switching from HSFO with 2.8% S (world average) to LSFO with 1.3% S.
If the FO system contains two service tanks and one settling tank, the dilution time will be the same as for the previous example if one of the service tanks is already filled with LSFO. The settling tank should be emptied (either by pumping the HSFO back to storage or by consumption), and refilled with LSFO prior to entering a SECA. If the FO system contains one service tank and one settling
tank, the changeover time will be substantially longer. The first point of blending is the settling tank and the blending volume will comprise of the settling tank, service tank and connected piping.
If the settling tank and service tank each contain FO for 12 hours of operation, and we assume one hour of FO in the piping, the dilution time is 240%*25h=60h.

It should be emphasised that this plot is a theoretical approximation with a built in safety factor, but without necessarily taking all operational procedures on board into consideration no guaranty can be given.

Fuel Oil Change over Calculator

Finally you can download Low Sulfur change over calculator produced by LR, in this