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IMOS - Bunker Interpolator

View IMOS Documentation in the Help Center.

On the Bunkers form, click 

 to initiate the Bunker Interpolator calculation.


The Bunker Interpolator uses daily ROB readings, along with data from the Boat Fuel Consumption Ratios Setup and Barge Fuel Consumption Setup forms to calculate estimated ROBs at arrival and departure and bunker consumption for each voyage leg. The data can be exported to a data warehouse where equipment performance can be analyzed and compared across various equipment owners to make more informed decisions.

Because ROB information is often received from Owners at times that do not correspond to arrivals and departures, arrival and departure ROBs must be interpolated based on historical ROBs obtained by owners.

  • The Bunker Interpolator takes two owner-provided ROB readings and calculates and stores the breakdown of consumption between the two readings. The Bunker Interpolator uses the following consumption categories:
    • Propulsion
    • Hotel (Port Consumption)
    • Discharge
    • Heating
    • Adjustment
    • Stop

The values calculated by the Bunker Interpolator appear on the Voyage Manager Bunkers tab and on the Voyage Bunkers form.

Total Fuel Consumption Calculation

The total consumption for a piece of equipment is calculated using the following formula:

(ROB at period start) + (bunkers lifted during the period)(bunkers transferred to the equipment during the period) - (ROB at period end) - (bunkers transferred from the equipment during the period)

  • For equipment that joined or departed the tow during the period, the ROB value from the corresponding Delivery, Redelivery, Join, or Depart rows (On the Activity Log Equip In/Out tab) will be used instead of the ROB at period start or ROB at period end values.
  • On the Activity Log Bunkers tab, if the Track Barge ROBs check box is not selected, the ROB value for barges will be zero.
    • For a barge entering a tow, if the ROB value is not zero and Track Barge ROBs is not selected, IMOS assumes that the fuel onboard the barge is immediately consumed upon joining the tow. A row appears, representing this consumption.
    • When Track Barge ROBs is not selected, you should not have a nonzero ROB for a barge departing the tow. If this situation occurs, the ROB amount will be used in the total consumption calculation.

Bunker Interpolator Calculation for Boats

  1. The Bunker Interpolator calculates the boat's total fuel consumption using the formula above.
  2. For each Laden, Ballast, and Hotel leg within the period, the Bunker Interpolator calculates the percentage of the overall period that the leg represents.
  3. For each fuel type that the boat consumed over the period, the Bunker Interpolator:
    1. Looks up the applicable row on the Boat form, using the number of barges as of the start date/time of the period. If the applicable row is not found, the Bunker Interpolator looks to the Boat Fuel Consumption Ratios Setup form. 
    2. Using the fuel consumption data generated from the previous step, calculates the boat's ROB at each Arrival and Departure within the period.
    3. Assigns all fuel consumed during the period to the appropriate categories: 
      • When the fuel consumption period is entirely at port (between a Port Start and a Port End), the difference in ROB's is categorized as Hotel. If the fuel consumption period includes sea time and port time, then the Hotel consumption calculation is (Number of days in port) * (Daily Hotel consumption rate).
        • The daily Hotel consumption rate is specified in the Hotel Gal/Day column on the Boat form. If the Hotel consumption rate is not specified on the Boat form, then the rate on the Boat Fuel Consumption Ratios Setup form will be used.
      • The remaining fuel is categorized as Propulsion fuel, which is further divided into laden and ballast, depending on the ratios specified on the Boat form or on the Boat Fuel Consumption Ratios Setup form.
      • Stop consumption is the fuel consumed during a Stop delay and is calculated similar to Port Consumption: (Stop delay days) * (Hotel consumption rate).
        • For example, if the Stop delay is 1 day, and the Hotel consumption rate is 20 gal/day, the Stop consumption is calculated as 1 * 20 = 20 gal. 

Bunker Interpolator Calculation for Barges

If the Track Barge ROBs check box is selected, a calculation is done for each barge that was in the tow over the period.

  • The Bunker Interpolator calculates the barge's total fuel consumption using the formula above.
    • If only Discharge or Heating consumption applies, all consumption is allocated to the Discharge or Heating category, respectively.
    • If both Discharge and Heating consumption applies:
      1. The Bunker Interpolator uses the Barge Fuel Consumption Setup form to determine the applicable Discharge consumption, in gallons per hour, and multiplies it by the length of each discharge operation to determine the number of gallons used for Discharging.
      2. The Heating consumption is calculated using the formula: (Total consumption) - (Discharging consumption).
      3. The barge's ROBs at each Arrival and Departure is calculated using the fuel consumption results from the previous steps.


  • You cannot run the calculation if any Voyage Period Journals of type Bunkers have been posted.
  • Heating consumption is calculated only if the Heated check box is selected for cargoes on the voyage.
  • Discharge consumption is calculated if the tow sailed to a type (Discharge) port during the period, and if an OS/OE activity type took place during the period.
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