Fuel Oil Outflow
- Last UpdatedDec 17, 2025
- 4 minute read
This module calculates the mean oil outflow parameter in accordance with "MARPOL, ANNEX 1 Regulation 12A - Oil fuel tank protection", paragraph 11, and compares this to the standard required.
Paragraphs 6, 7 and 8 of Regulation 12A, specify the location of fuel oil tanks to minimize the risk of pollution in the event of damage to the vessel. Paragraph 11 provides an alternative method of evaluating the risk pollution based on probabilistic principles. This module is only concerned with this alternative method.
Note:
MARPOL ANNEX 1 Regulation 12A only applies to ships with an aggregate oil fuel capacity
greater than 600 m3.
The module calculates the mean oil outflow for side and bottom damage (Oms and Omb) and combines them into a mean oil outflow index, Om = (0.4Oms + 0.6Omb)/C, where C is the total fuel oil capacity of the vessel.
The mean oil outflow index must be less than 0.0157 - 1.14E-6.C, where C < 5000 m3, or 0.010, where C >= 5000 m3.
The mean outflow for side damage, Oms, is calculated as the sum of Ps.Os for each tank, where Ps is the probability of penetrating the oil fuel tank, calculated from tables given in the rules, and Os is the outflow, in m3, from side damage.
Similarly, the mean outflow for bottom damage, Omb, is calculated as the sum of Pb.Ob.Cdb for each tank, where Pb is the probability of penetrating the oil fuel tank, calculated from tables given in the rules, Ob is the outflow, in m3, from bottom damage, and Cdb is a factor to account for oil capture, which is 0.6 if the tank is bounded below by non-oil tanks, and 1.0, if not.
For bottom damage, the ship is assumed to be grounded, and consequently, Obm depends on the tidal change. For the regulations, outflow due to bottom damage is calculated at two tide conditions, zero and minus 2.5 m, and Omb = 0.7 Omb(0) + 0.3 Omb(2.5)
There are also special rules concerning tanks bounded by the bottom shell. In practice, this may mean that ships with fuel oil tanks in the double bottom, are unlikely to comply with Regulation 12A.
Input dialog
The grid displays a list of compartments in the ship. The list can be filtered using the Category Filter. For example, selecting ‘FO Fuel Oil Tanks’, in the above example, will display only compartments assigned to this category.
Note:
This module, only deals with fuel oil tanks.
All fuel oil tanks, should be selected by checking the Select box. (In the above example, the unchecked tanks, will have to be re-categorised, as the vessel does not comply, if they are used as fuel tanks.)
Other input items are described below:
|
Item |
Description |
|---|---|
|
Length, L |
96% of the total length on a waterline at 85% of the least moulded depth measured from the top of the keel, or the length from the foreside of the stem to the axis of the rudder stock on that waterline, if that be greater. If the associated check box is ticked, then the program will calculate this value. |
|
AP to aft terminal of L |
Distance from the AP to the aft terminal of L (positive if terminal is aft of the AP). This will also be calculated, if the Length checkbox is ticked. |
|
Breadth mld., B |
Maximum moulded breadth of the ship. |
|
Depth to Upper Deck, Ds |
Moulded depth measured at mid-length to the upper deck at side. |
|
Loadline Draft, ds |
Vertical distance from the moulded baseline at mid-length to the waterline corresponding to the summer freeboard draft to be assigned to the ship. |
|
Lightship Draft, dls |
Moulded draft amidships corresponding to the lightweight. Note: |
|
Max. Breadth at ds, Bs |
Greatest moulded breadth, at or below the deepest loadline draft, ds. If the associated checkbox is ticked, then the program will calculate this value. Note, however, that the program will assume the greatest value will be at the loadline draft. If this is not the case, then you should specify the value. |
|
Max. Breadth at 30% Ds, Bb |
Greatest moulded breadth, at or below the waterline (db) at 30% of the depth, Ds. If the associated checkbox is ticked, then the program will calculate this value. Note, however, that the program will assume the greatest value will be at the draft, db. If this is not the case, then you should specify the value. |
|
Tidal Change |
Tidal change. Reductions in tide shall be expressed as negative values. For the purposes of this regulation, tc should be set to -2.5 m. |
|
Fuel Oil Density |
Nominal density of the oil fuel. This shall generally be taken as 1.000 kg/m3. If the density of the oil fuel is specifically restricted to a lesser value, the lesser value may be applied. |
|
Compartment names |
Option for displaying the compartment identifier, long name, or both in the output tables. |
|
Include Frames |
If this box is checked, then the frame numbers corresponding to the aft and forward limits of the compartment, will be included in the output tables. |