Tanker Cargo Calculations - ASTM Tables Usage & Procedure of

Calculations

Hi,

In my recent meetings with a variety of Ship's officers, including some Engineers,

who were interested in knowing more of this, I've realized that no training institute
actually gives them a complete picture of Tanker cargo calculations.
It is really amusing to note that some of these people, I've had to prepare for vettings
etc. or for that matter, just for preparing for the vessel, are senior officers on board.

Anyhow, below is a concise effort to introduce all to these calculations. As usual,

please feel free to contact self for more info, and share as much as you want. Do let
me know, if something is not correct.

One more note: The below is usually not applicable to Chemical cargoes in liquid
bulk, since the ASTM tables are normally not applicable there.

Series I - TABLE 5 & 6 - FOR API, OF, 60OF

Volume I: Generalized Crude Oils (Tables 5A & 6A)
Volume II: Generalized Products (Tables 5B and 6B)
Volume III: Individual and Special Applications (Table 6C)

Series II - TABLE 23 & 24 - FOR RELATIVE DENSITY,  oF, 60oF

Volume IV: Generalized Crude Oils (Tables 23A & 24A)
Volume V: Generalized Products (Tables 23B and 24B)
Volume VI: Individual and Special Applications (Table 24C)

Series III - TABLE 53 & 54 - FOR KG/cm3 DENSITY, oC, 15oC

Volume VII: Generalized Crude Oils (Tables 53A & 54A)
Volume VIII: Generalized Products (Tables 53B and 54B)
Volume IX: Individual and Special Applications (Table 54C)

Volume X: Background, Documentation, Program Listings

Volume XI / XII - ASTM D 1250-80 - API standard 2540 and IP Designation 200 apply

Volume XI - ENTRY WITH API GRAVITY

Table 1 Interrelation of Units of Measurement
Table 2 Temperature Conversions
Table 3 API Gravity at 60oF to Relative Density 60/60oF and to Density at 15oC
Table 4 U.S. Gallons at 60F and Barrels at 60F to Litres at 15C against API Gravity at 60F
Pounds per US Gallon at 60F and US Gallons at 60F per pound against API
Table 8 Gravity at 60F
Short Tons per 1000 US Gallons at 60F and Barrel at 60F against API Gravity at
Table 9 60F
Table 10 US Gallons at 60F and Barrels at 60F per Short Ton against API Gravity at 60F
 Long Tons per 1000 US Gallons at 60F and per Barrel at 60F against API Gravity
Table 11 at 60F
Table 12 US Gallons at 60F and Barrels at 60F per Long Ton against API Gravity at 60F
Metric Tons per 1000 US Gallons at 60F and per Barrel at 60F against API
Table 13 Gravity at 60F
Table 14 Cubic Metres at 15C per Short Ton and per Long Ton against API Gravity at 60F

Volume XII - ENTRY WITH RELATIVE DENSITY

Table 21 Relative Density 60/60oF to API Gravity at 60oF and to Density at 15oC
Table 22 US Gallons at 60F to Litres at 15C and Barrels at 60F to Cubic Metres at 15C
Pounds per US Gallon at 60F and US Gallons at 60F per Pound against Relative
Table 26 Density 60/60F
Short Tons per 1000 US Gallons at 60F and per Barrel at 60F against Relative
Table 27 Density 60/60F
US Gallons at 60F and Barrels at 60F per Short Ton against Relative Density
Table 28 60/60F
Long Tons per 1000 US Gallons at 60F and per Barrel at 60F against Relative
Table 29 Density 60/60F
US Gallons at 60F and Barrels At 60F per Long Ton against Relative Density
Table 30 60/60F
Cubic Metres at 15C per Short Ton and per Long Ton against Relative Density
Table 31 60/60F
Specific Gravity Reduction to 60F for Liquefied Petroleum Gases and Natural
Table 33 Gasoline
Reduction of Volume to 60F against Specific Gravity 60/60F for Liquefied
Table 34 Petroleum Gases
Table 51 Density at 15C to Relative Density 60/60F and to API Gravity at 60F
Table 52 Barrels at 60F to Cubic Metres at 15C and Cubic Metres at 15C to Barrels at 60F
Kilograms per Litre at 15C and Litres at 15C per Metric Ton against Density at
Table 56 15C
Table 57 Short Tons and Long Tons per 1000 Litres at 15C against Density at 15C
Table 58 US Gallons and Barrels per Metric Ton against Density at 15C

Volume XIII: LUBRICATING OILS, TABLES 5D & 6D

Volume XIV: LUBRICATING OILS, TABLES 53D & 54D

Please remember that normally the density or API is provided by the terminal or surveyor in the load ports and what
is used will be dependent on the region / port of loading. For example in USA / Canada, Persian Gulf, API usage is
prevalent, while entire of Europe and Asia uses Density at 15C. However please ascertain, if Density at 15C is
provided, whether it is in air or in vacuum. This is very important when finding out from Table 54, since the density
provided there is in Air and hence same must be used. (Density at 15C in Air = Density at 15C in Vacuum - 0.0011
 PROCEDURE OF CALCULATIONS
Working with Density at 15oC in air:
1)  Observed Ullage - apply corrections - get Corrected Ullage
2)  Observed Interface - apply corrections - get Corrected Interface
3)  From Corrected Ullage, find Total Observed Volume TOV (in cubic metres)
4)  From Corrected Interface, find Volume of Water (in cubic metres)
5)  TOV - Water = Gross Observed Volume (GOV) of Cargo (in cubic metres)
6)  Use Density at 15C and Observed Temperature (oC) and find Volume Correction Factor (VCF) from Table 54
7)  Gross Standard Volume (GSV) = GOV x VCF (cubic metres)
8)  Weight Correction Factor (WCF) = Density at 15C in vacuum - 0.0011 (or the Density at 15C in air)
9)  Weight in Air (Metric Ton) = GSV x WCF(Density at 15C in air)
10) Weight in Vaccum (Metric Ton) = GSV x Density at 15C in vacuum

Working with API Gravity at 60oF :

1)  Observed Ullage - apply corrections - get Corrected Ullage
2)  Observed Interface - apply corrections - get Corrected Interface
3)  From Corrected Ullage, find Gross Observed Volume (in US Barrels)
4)  From Corrected Interface, find Volume of Water (in US Barrels)
5)  GOV - Water = Observed Volume of Cargo (in US Barrels)
6)  Use API Gravity at 60F and Observed Temperature (oF) and find Volume Correction Factor (VCF)
from Table 6
7)  Gross Standard Volume (GSV) = Observed Cargo Volume (Barrels) x VCF (in US Barrels)
8)  Find Weight Correction Factor (WCF) from Table 13
9)  Weight in Air (Metric Tons) = GSV x WCF

Working with Relative Density at 60/60oF :

1)  Observed Ullage - apply corrections - get Corrected Ullage
2)  Observed Interface - apply corrections - get Corrected Interface
3)  From Corrected Ullage, find Gross Observed Volume (in cubic metres)
4)  From Corrected Interface, find Volume of Water (in cubic metres)
5)  GOV - Water = Observed Volume of Cargo (in cubic metres)
6)  Use Relative Density at 60/60F and Observed Temperature (oF) and find Volume Correction Factor (VCF) from Table
24
7)  Gross Standard Volume (GSV) = Observed Cargo Volume (m3) x VCF (in m3)
8)  Weight in Air (Metric Ton) = GSV x Relative Density at 60/60F

Total observed volume (TOV)

The total volume of material measured in the tank including cargo (oil or chemical), free water (FW), entrained sediment and
water (S&W), sediment and scale as measured at observed temperature and pressure.
Free water (FW)
Water layer existing as a separate phase in the tanks, normally detected by water-paste or interface detector and usually
settled at the bottom of the cargo tank  depending on relative density of the cargo.

Sediment & Water (S&W or BS&W)

Entrained material within the oil bulk, including solid particles and dispersed water, also sometimes known as base sediment
and water (BS&W). Expressed always as a percentage of the total cargo quantity, is found out be collecting average sample
of the cargo inline during transfer and calculated by centrifuge technique in a laboratory.

Gross observed volume (GOV)

It is the Total Observed Volume (TOV) less free water (FW) and bottom sediment, being the measured volume of product
and sediment & water (S&W) at observed temperature and pressure. Bottom sediment are normally not present on board a
chemical or clean oil product tanker and therefore not deducted whereas it may be present in a dirty oil carrier, but be very
difficult to ascertain.

Gross standard volume (GSV)

It is the measured volume of product and S&W at standard conditions of 15°C and atmospheric pressure. In practice is the
GSV the GOV multiplied by the volume correction factor (VCF) obtained from the appropriate ASTM/IP Petroleum
Measurement Tables.

Net standard volume (NSV)

It is normally applicable only to Crude Oils. NSV is the GSV minus S&W, being a measurement of the dry oil quantity at
standard conditions. For clean oil products and chemicals, the S&W is not normally included within the receiver's quality
specifications.

The term Weight in Air  is that weight which a quantity of fluid appears to have when weighed in air against standard
commercials weights so that each will have a mass (weight in vacuum) equal to the nominal mass associated with it.
The term Weight in Vacuum refers to the true mass of a fluid.

USE OF WEDGE FORMULA FOR OBQ / ROB CALCULATIONS & FREE WATER
CALCULATIONS

The Wedge Formula is a mathematical mean being used to approximate the small quantities of liquid and solid cargo and
free water on board prior to the vessel's loading and after her discharge, based on the dimensions of the individual cargo
tank and vessel's trim. The Wedge Formula is to be used only when the oil liquid does not touch all bulkheads of the vessel's
cargo tank, that is to say the liquid oil lying in small pools among the bottom sediment.

In order to standarise the OBQ/ROB calculations on board the Crude Oil carrying tanker vessels, the following geometric
form of the Wedge Formula shall be used and this form of the formula assumes that the cargo tank is 'box shaped' with no
internal 'deadwood' or pipeline systems, heating coils etc. that would impact the accuracy of the volume calculated from the
sounding. Furthermore this wedge formula calculation makes the enormous assumption that any 'liquid' found in a cargo tank
is in the form of a regular wedge shape with its base at the aft bulkhead of the cargo tank.
It is obvious that such a series of assumptions normally can invalidate the absolute accuracy of the calculation immediately
given, amongst other issues, the shape of the wing tanks (the turn of the bilge) and in particular those wing tanks at the fore
and aft parts of the vessel.

The calculation method for the Geometric edition of the Wedge Formula:
Assumption: Given the small angle involved with the trim of the vessel, then the 'Sine' of an angle can be considered as the
same as the 'Tangent' (Tan) of an angle and consequently:

Step 1:
Correct the position of the sounding position with respect to the aft bulkhead of the cargo tank due to the trim of the vessel,
distance = A

A = Tank Reference Height (Observed Height) x Tan X;

where X = the Trim angle of the vessel and;
Tan X = (Aft draft - Forward draft) / Length Between Perpendiculars (L.B.P.) of the vessel.

Step 2:
Determine the distance of the apex of the wedge from the aft bulkhead for obtaining information whether:
(1) should a Wedge Formula be used at all (kindly note that a wedge formula is not applicable if: 
     (a) the liquid surface covers the total cargo tank bottom or the calculated apex of the wedge is at or beyond the forward
bulkhead of      
          the cargo tank or: 
     (b) it is sludge ROB volumes only);
And
(2) whether the wedge is a regular wedge (which can be checked by comparison with alternative soundings being taken).

S = Observed Sounding;

F  (Distance of the apex of the wedge from the sounding position) = S x Tan X;
E (Distance of the apex of the wedge to the aft bulkhead) = (F - A) + B;
where B is the distance on deck from the point of sounding to the aft bulkhead.

Step 3:
Determine the depth of the wedge at the aft bulkhead of the cargo tank, depth = D;  D = E x Tan X

Step 4:
Knowing D (sounding depth at the aft bulkhead) and E (the distance from the aft bulkhead to the apex of the wedge), then
the area of the longitudial cross section of the wedge may be calculated,
thus as the area of a triangle = (Base x Height) / 2 then; (D x E) / 2 = cross sectional area of wedge.

Step 5:
Having obtained the cross sectional area of the wedge, the volume of the wedge is calculated by multiplication by the
breadth of the cargo tank (please note that the breadth of the cargo tank should be measured at the bottom of the tank at the
aft bulkhead position and not at deck level or elsewhere within the cargo tank).
Volume of the Wedge = Cross sectional Area x Breadth of Tank

Throughout this calculation it is very important that all distances are in metres. Do not use centimetres for the observed
sounding.

Alternatives:

Regardless above stated requirement, an I.S.O. standard method is also available in the event that any Cargo Inspector do
not accept the geometric edition of the wedge formula. This method depends upon the accuracy of the vessel's tank ullage
calibration tables for the larger ullages / smaller soundings in the cargo tank. If the tank calibration tables are accurate for
this region of the cargo tanks, then this method will give added accuracy to the general method of calculating tank residues
after discharge.
This method is as follows:

Step 1:
Calculate DA (the Corrected liquid sounding at the aft bulkhead position);  DA = D + {f(Y - (H x f))}
where:
D is the observed liquid sounding;
f  is the Trim factor ( TS  / LS );
TS  is the vessel's trim;
Y is the distance of the sounding point to the aft bulkhead;
H is the reference height of the cargo tank;
LS  is the vessel's Length Between Perpendiculars.

Step 2:
Calculate Ct  (the Tank constant); Ct  =  LS  / ( 2 x TS  x Lt ) (where Lt is the Length of the Cargo Tank).

Step 3:
Calculate the 'k' coefficient;   k = DA  x Ct
if k > 0.5 wedge is not required to be carried out;
if k = 0.5 wedge must be carried out.

Step 4:
if k > 0.5 then calculate the volume of the liquid contained in the cargo tank from the calibration tables using the Observed
sounding, D, applying the trim corrections.

Step 5:
if k = 0.5 then calculate DX (the wedge sounding).   DX = DA  / 2

Step 6:
Enter the cargo tank calibration tables with DX, without applying trim corrections to equivalent volume VO.

Step 7:
Calculate the liquid wedge volume V1;   V1 =  VO  x  2  x  k

In addition to above methods it should be noted that if the procedures as specified in the vessel's COW manual are being
followed for the determination of the 'Dryness' of a cargo tank, namely, the sounding of the residues in four(4) differing
locations within the cargo tank, then the foregoing methods of calculations can be avoided.
Assuming the shape of the individual cargo tanks is fairly regular / constant in a fore and aft direction and, notwithstanding
the fact that the vessel will be significantly trimmed by the stern, then the four measurements, as suggested in the COW
Manual guidelines, as obtained by sounding can be used to calculate an average sounding so as to obtain a single sounding.
The single average sounding can be used directly in order to obtain an equivalent volume from the vessel's tank ullage
calibration tables
Such a method will provide a clearer indication as to the type and nature of the residues on the cargo tank floor as well as
provide much clearer indications as to the profile of the residues within the cargo tanks.
The shipboard loading survey is conduted to get the quantity loaded onboard the vessel with
measurement of cargo tank. The sounding or ullaging are performed to obtain the level of oil
and free water on each tank. The obtained oil level data were calculated by using ship tank
table to get TOV and total free water.
Data required for Crude Oil Survey:
– Tank Number
– Tank Reference Height
– Dip innage (sounding) or ullage
– Free water dip (FW)
– Oil temperature (C or F)
– Oil density or API
– BS&W volume in % (as per analysis result)

ASTM Table uses for calculation:

For Crude Oil
API
– Table 6 (to convert GOV to GSV)
– T11 (to convert GSV to Long Ton)
– T13 (to convert GSV to Metric Ton)
– Temperature in F, Quantity or volume in Barrels (Bbls)
Density
– Table 54 (to convert GOV to GSV)
– T56 (to convert GSV to Metric Ton)
– T57 (to convert GSV to Long Ton)
– Temperature in C, Quantity or volume in Cubic Meter (M3)
For Product Oil:
API
– Table 6B (to convert GOV to GSV)
– T11 (to convert GSV to Long Ton)
– T13 (to convert GSV to Metric Ton)
– Temperature in F, Quantity or volume in Barrels (Bbls)
Density
– Table 54B (to convert GOV to GSV)
– T56 (to convert GSV to Metric Ton)
– T57 (to convert GSV to Long Ton)
– Temperature in C, Quantity or volume in Cubic Meter (M3)
The Shipboard calculation information pertaining to loading:
Ship Before Loading
– On Board Quantity (OBQ) total volume (included slops if Load On Top – LOT)
– On Board Quantity (OBQ) free water (included slop water if Load On Top – LOT)
– Ballast Quantity
– Slop tanks TCV, GSV, NSV
– Quantity of slop water decanted on voyage
Ship After Loading
– TCV
– Free water volume
– GSV, NSV
– Gross Weight in air
– Oil temperature
– Suspended water (% volume) BS%W (Bottom Sediment and Water)
– API Gravity
Ship Loaded figures
– TCV, GSV,
– Gross weight in air
– VEF (Vessel Experience Factor)
– TCV ship/shore different (VEF not applied)
– TCV ship/shore different (VEF applied)
– Bunker Quantities.
Step of Calculation of Crude oil
TOV – FW = GOV
GOV x VCF (Table 6 @F or Table 54 @C) = GSV
GSV x WCF (Table 11 or Table 57 = Gross Long Ton (GLT)
GSV x WCF (Table 13 or Table 56 = Gross Metric Ton (GMT)
GSV x BS&W Factor = NSV
GLT x BS&W Factor = Net Long Ton (NLT)
GMT x BS&W Factor = Net Metric Ton (NMT).
Sample of Calculation of Crude oil using ASTM Table 6
Tank No. 1 Center.
Ullage at 2.10 Meter, Free water dip : 3.00 cm.
Volume as per tank table Oil : 108,330 Bbls and water : 51 Bbls
API : 37.50, Temperature : 117.0 F,
BS&W : 0.10%, BS&W factor = 1 – (1 x BS&W%) = 0.999
Calculating Figures
TOV = 108,330 Bbls, FW = 51 Bbls.
GOV = 108.330 – 51 = 108,279 Bbls.
VCF = 37.50 @ 117.0 F = 0.97385.
WCF to GLT = Table 11 @ API = 0.13071.
WCF to GMT = Table 13 @ API = 0.13281.
GSV = GOV x VCF = 108,279 x 0.97385 = 105,448 Bbls.
GLT = GSV x WCF = 105,448 x 0.13071 = 13,783.108 LT.
GMT = GSV x WCF = 105,448 x 0.13281 = 14,004.549 MT.
NSV = GSV x BS&W Factor = 105,448  x 0.999 = 105,343 Bbls.
NLT = GLT x BS&W Factor = 13,783.108 x 0.999 = 13,769.325 LT.
NMT = GMT x BS&W Factor = 14,004.549 x 0.999 = 13,990.544 MT.
The above is a brief step and calculation for petroleum survey on shipboard. In the next post,
“if any convenience time”, I will write some short post about shoretank calculation, VEF,
wedge, and gas tanker.
You could also download the simple trial software for above calculation at link 7s-OilCal-
T6.T54-Trial – Password : 123456 (size: 4.6 mb). Your comment and advice would be
appreciated.
Regards,
Surveyor.
Definitions - Petroleum Measurement Standards - Marine Measurement
API Gravity (relative density) is a means used by the petroleum industry to express the density of petroleum
liquids.  API gravity is measured by a hydrometric instrument having a scale graduated in degrees API.  The
relation between API gravity and relative density (formerly called specific gravity) is :

API Gravity 60oF = (141.5 / Relative Density 60oF/60oF) - 131.5

Automatic Sampler is a device used to extract a representative sample from the liquid flowing in a delivery pipe. 
The automatic sampler generally consists of a probe, a sample extractor, a flow meter, a controller and a sample
receiver (container).

Ballast is the water that is taken on when a vessel is empty or partly loaded to increase draft to properly submerge
the propeller and maintain stability, trim and list.

Clingage is the cargo that adheres to all surfaces of the emptied portion of the tank other than bottom surfaces.

Crude Oil Washing ( Go to Tank Washing)

Cargo Quantity Option Certificate is a certificate signed by the vessel and shore representatives acknowledging
the amount of cargo intended to be loaded.  Generally, most product cargoes have a tolerance based on either
supplier, receiver or vessel capabilities.  Each party involved with the loading shall agree to the quantity to be
loaded.

Draft is the depth of a vessel below the water line measured from the surface of the water to the bottom of
vessel's keel.  The draft can be taken at six positions (forward, amidships, aft - port and starboard side). 
Deviations from measured and calculated figures usually relate to deviations in the known constant and
hog/stress.

Free Water (FW) is the volume of sea water (or other water contamination) that is in a container that is not in
suspension in the contained liquid (oil).  See also definitions for sediment and water.

Gross Observed Volume (GOV)  (Go to Volumes)

Gross Standard Volume (GSV)  (Go to Volumes)

Gross Observed Weight (GSW)  is the total weight of all petroleum liquids and sediment and water (if any),
excluding free water, as determined by applying the appropriate weight conversion factors to the gross standard
volume.

Indicated Volume  (Go to Volumes)

Inerting is a procedure used to reduce the oxygen content of a vessel's cargo spaces to 8 percent or less by
volume by introducing an inert gas such as nitrogen, carbon dioxide or a mixture of gases such as boiler / inert
gas generator flue gas.

Innage gauge (dip sounding) is the measured distance from the surface of the liquid to a fixed datum plate or to
the bottom of the tank.

Letter of Protest (Notice of Apparent Discrepancy) is a letter issued by any participant in a custody transfer citing
any or all the conditions of dispute.  This letter serves as a written record that the particular action or finding was
questioned at the time of occurrence.  The letter usually has a paragraph reserving the issuer's right to refer to
matter at a later date.

Liquid volume is the measurable amount of material that is free flowing at the time of measurement.

List (Heel) is the leaning or inclination of a vessel, expressed in degrees port or starboard.  If found to be other
than zero, list correction tables are to be used to correct the measured ullage or sounding to compensate for the
measured list.  See next paragraph.

List (Heel) correction is the correction applied to the observed gauge or observed volume when a vessel is listing,
provided that the liquid is in contact with all the bulkheads in the tank.  Correction for list may be made by
reference to the vessel's list correction tables for each individual tank or by mathematical calculations.

Load on Top is defined as both a procedure and a practice.

     Procedure: Load on top is the shipboard procedure of collecting the settling water and oil mixtures, resulting
from ballasting and tank cleaning operations (usually in a special slop tank or tanks), and subsequently loading
cargo on top of the slops and pumping the resultant mixture ashore at the discharge port.

     Practice: Load on top is the act of commingling onboard quantity with cargo being loaded.  The onboard
quantity is the remnant of the previous cargo or part load into the tank.

Multipoint gauging is the activity of measuring cargo in a vessel tank through two or more openings in the top of
the tank.

Net Standard Volume (NSV)  (Go to Volumes)

Net Standard Weight (NSW) is the total weight of all petroleum liquids, excluding sediment and water and free
water, determined by deducting the S&W weight from the Gross Standard Weight (GSW).

Non-liquid volume is the measurable amount of material that is not free flowing at the time of measurement.  Non-
liquid material may include anyone or a combination of hydrocarbon waxes, water/oil emulsions, sediment, or
solidified cargo.

On-board quantity (OBQ)  (Go to Volumes)

Observed Reference Height is the distance actually measured from the tank bottom or datum plate to the
established reference point.

Reference Height is the distance from the tank bottom to the established reference point or mark.

Reference Point is the point from which the reference height is determined and from which the ullages / innages
are taken.

Remaining On Board (ROB)  (Go to Volumes)

Sediment and Water (S&W) is the non-hydrocarbon solid material and water in suspension in petroleum liquid. 
Sediment and water is measured by the techniques described in MPMS Chapters 10.1 ~ 10.8 of Appendix A.

Slops are oil, oil/water/sediment, and emulsions contained in the slop tanks or designated cargo tanks.  The
mixture usually results from tank stripping, tank washing, or dirty ballast phase separation.
Stop Gauge is a pre-transfer determination of a specific volume of cargo represented by a specific tank level,
which, when reached, results in cargo completion of the transfer.  This determination may be done by either shore
or vessel personnel.

Tank Washing is divided into two types of activities:

     Water Washing involves the use of high-pressure water stream to dislodge clingage and sediment from the
bulkheads, bottom and internal tank structures of a vessel.

     Crude Oil Washing (COW) involves the use of a high-pressure stream of the crude oil cargo to dislodge or
dissolve the clingage and sediment from the bulkheads, bottom and internal tank structures of a vessel during the
discharge operation.

It must be noted that regulatory agencies (including most ship / facility internal documented procedures require
the tanks to be inerted during tank cleaning.

Total Calculated Volume (TCV)  (Go to Volumes)

Total Observed Volume (TOV)  (Go to Volumes)

Trim is the condition of a vessel with reference to its longitudinal position in the water.  It is the difference between
the forward and aft drafts and expressed "by the head" if the forward draft is deeper than the aft draft or "by the
stern".

Trim Correction  is the correction applied to the observed gauge or observed volume when a vessel is not on an
even keel (equal forward and aft drafts), provided that the liquid is in contact with all bulkheads in the tank. 
Correction for trim may be made by referencing trim tables for each individual tank or by mathematical calculation.

Ullage Gauge (Outage) is the measured distance from the cargo liquid surface to the reference point.

Vessel Experience Factor (VEF) is a compilation of the history of the total calculated volume (TCV) vessel
measurements, adjusted for on-board quantity (OBQ) or remaining on board (ROB), compared with the TCV
shore measurements.  Separate VEFs should be developed for loadings and discharges.  The information used to
calculate VEF should preferably be based on documents that follow accepted industry standards and practices,
such as inspection company reports.

It may be noted that for the purpose of calculating a load or discharge vessel ratio, the TCV on board the vessel
includes all petroleum liquids, sediment and water, free water and slops found after loading (TCV sailing volume)
or before discharge (TCV arrival volumes).  However, if in the completion of the Sequential Voyage Log, a TCV
ratio (vessel - shore) appears to be in gross error, the ratio may be deleted with the agreement of both parties.  If
all qualified voyages are based on load/discharge data from the same terminal, the applicability of those VEF data
to the loads/discharges at other terminals should be evaluated.

Vessel Load Ration (VLR) is the total calculated volume (TCV) by the vessel measurement upon sailing, less on-
board quantity (OBQ), divided by the TCV by shore measurement at loading -

     VLR = (TCV on sailing - OBQ) / TCV received from shore at loading

Vessel Discharge Ration (VDR) is the total calculated volume (TCV) by the vessel measurement on arrival, less
remaining on-board (ROB), divided by the TCV by shore measurement at discharge -

     VDR = (TCV on arrival - ROB) / TCV received from shore at discharge

Volume Correction Factor (VCF) is the numerical value determined by laboratory analysis or by standardized
computer arithmetic that when multiplied by the Gross Observed Volume at tank temperature results in the
volume of the product at its standard temperature (15 oC or 60oF).  The factors applicable for bands of API (relative
density) and temperature are available in standard tables booklets or may be computed using a standardized
format.  If the VCF is below 1 it is shown accurate to 5 places of decimal otherwise it is shown in 4 places of
decimal.

Using an Innage Tape and Bob

a. After safely grounding, the innage tape and bob should be lowered into the tank until the bob is a short
distance from the bottom, as determined by the tape reading at the reference point
b. The tape should then be unwound slowly until the tip of the bob just touches the bottom or datum plate. If
the tape is lowered too far, the bob will tilt and an incorrect gauge will be obtained.
c. The tape reading at the reference point should be recorded, as well as any variance from the reference
height.
d. The liquid cut on the tape should be read and recorded as the innage. (A suitable oil-indicating paste or
grease or a light lubricating oil may be used to facilitate reading the cut.  The use of chalk or talcum
powder is not recommended, since oil or product has a tendency to creep on a chalked tape.)

Alternative Innage Procedure

An ullage gauge may be converted to an innage gauge by subtracting the ullage from the reference height shown
on the capacity tables.

Open Free-Water Measurement

The use of water-indicating paste in conjunction with innage or ullage procedures provides a measurement of the
free water in a vessel's tanks. The recommended procedure for free-water gauging is by the innage method. If the
level of the water being measured is high enough to show a cut on or above the tape clip, a larger gauge bar
should be used. How- ever, if measurement conditions dictate, it may be necessary to utilize the ullage method or
other methods as agreed upon by all the parties. For measurement under adverse conditions.

Vessel tanks should be gauged for free water using water-  indicating paste or other equipment agreed upon by
the par- ties involved. Measurements should be taken independently of any other innage or ullage measurements
and should be properly recorded. Free water should be measured at both the loading and the discharging port.

Using an Innage Tape and Bob To Measure Free Water

a. Apply the water-finding paste on the bob or bar sufficiently high to measure the anticipated level of water
(see note 2).

b. After grounding, .the innage tape and bob should be lowered into the tank until the bob is a short distance
from the bottom, as determined by the tape reading at the reference point.

c. The tape should then be unwound slowly until the tip of the bob just touches the bottom or datum plate. If
the tape is lowered too far, the bob will tilt and an incorrect gauge will be obtained.

d. Once the bob touches bottom, keep it there long enough for the paste to react to the water (see note 3).

e. Withdraw the tape and read and record the highest, clearly defined water cut (see notes 4 and 6).
 f. Repeat steps a through e until two identical readings are obtained.

g. Record the cut as "clearly defined," "speckled," or "slightly discolored." Measurement of free water on
vessels that are out of trim is addressed in MPMS section 9.7.

Note 1: There are many brands of water-indicating pastes available that change color on contact with free water.
It should be noted, however, that all brands may not react the same in the presence of water. Accordingly, the
following qualities should be known before selecting a water paste:

a. Clarity of color change.

b. Ability to "shed" oil.

c. Shelf life.

d. Ease of application to the bar and ability to "grip" the bar.

e. Dense enough not to wash off when passing through the oil.

Note 2:   It is recommended that two different pastes be applied on the bar for each free water innage gauge at
the beginning of gauging. After it has been established which paste yields the highest, continuous clear water cut,
the other can be discontinued.  'When applying the two pastes to the bar, cover a little less than one-half of the
entire surface of the round bar with each paste.  Make sure that the measurement scale remains free of paste.
The coating of paste on the bar should be thin but opaque.

Note 3:   Allow the paste-coated bar to remain in the gauging position for a minimum of ten seconds for gasoline,
kerosene, and similar light products, and one-to-five minutes for heavy, viscous products (or as otherwise
specified by the manufacturer).  This amount of time is required to shed the petroleum that adheres to the paste.
in heavy viscous petroleum, apply an even film of light lubricating oil over the paste to facilitate the shedding of
the petroleum from the paste (see 9.1).

Note 4:   When the bob or bar is removed to read the water cut, do not blow or wipe the petroleum off the paste
as this may distort the clarity of the water cut. If the water cut is obscured by the petroleum (black oils), wash the
surface of the paste with a suitable solvent. The solvent should be poured or lightly sprayed on the paste-covered
bar well above the anticipated cut and allowed to rinse down over the cut area. Pouring directly on the paste may
distort the clarity of the water cut.

Note 5: Wipe the bar clean after gauging each tank and re-apply paste before gauging subsequent tanks.

Note 6:   If the paste on one side is spotted or lower than the other, record the highest level reading as the official
measurement of free water level.  Oil adhesion may cause low readings, but will not cause high readings. 
Spotting may indicate a layer of emulsified oil and water or that the product did not completely shed off the paste.

If water cuts indicate that an emulsion layer may be present, read and record both the clear cut and the height of
the spotting measurement.

Survey Documentation - Open Measurement Equipment and Procedures

Open OBQ / ROB Measurement
OBQ and ROB volumes may be determined by either the innage or the ullage method.  Liquid material is usually
innaged. Solid material must be ullaged.  ROB should be measured after lines (hoses) have been drained into the
vessel.  By draining lines (hoses) to a single small tank, ROB may be measured more accurately.

When a vessel is out of trim, some OBQ and ROB quantities may not be measurable at the proper gauge points. 
In these circumstances, more extensive methods of volume determination may be necessary, and additional
measurements will usually be required.

Safety and operational considerations must always be factors in determining what actions can be taken, but in all
situations, existing conditions and the specific actions taken to measure ROB and OBQ must be noted in the
report. 

Liquid cargo should only be trim and/or list corrected if the liquid is in contact with all bulkheads.  When the liquid
is not in contact with all bulkheads, a wedge correction should be applied.  In all circumstances, the cargo
documents should include the vessel's list and trim.  The nature of the material in the tank should be described in
detail, and the conditions of measurement and other pertinent information should be noted.  For calculation of
small quantities, refer to API M-PMS Chapter 17.4.

Note: Wedge, trim, and list corrections do not normally apply to sediment and sludge but may apply to solidified
(non-liquid) cargo.  In addition, when the wedge formula or wedge tables are used, extreme care must be
exercised to ensure that wedge does exist, that the measured material is not just a puddle under the gauge hatch,
and that the formula used is applicable to the actual shape of the tank (that is, it accounts for the curve of the
bilge).  Measures to be taken in such a case should include-but are not necessarily limited to-taking ROB
measurements at more than one point in the tank.  This would verify the existence of a wedge and the extent of
cargo solidification.

Open Temperature Determination The temperature of the cargo being measured is one of the most important
elements needed to accurately determine its volume.  This section fully describes the equipment and procedures
that should be used to manually obtain the cargo's temperature.

Open Temperature Measurement Equipment All temperature equipment must be safe for use with the material
whose temperature is to be obtained.  The preferred method of obtaining temperatures of the liquid in a vessel's
tanks is to use a portable electronic thermometer (PET).  Alternately, a mercury-in-glass thermometer with etched
glass face may be used.

Thermometers used for custody transfer should be properly calibrated and their accuracy verifiable and traceable
to a NlST standard thermometer and meet the requirements specified in API MPMS Chapter 7.

Thermometers

Thermometers are precision instruments and should be handled with care.  For a technical description of the
specifications of each type, refer to API MPMS Chapter 7.

Field Verification of Temperature Equipment

All thermometers used for custody transfer measurements should be verified for accuracy before initial use, and
at least once a year thereafter.  In addition, before each use or once per day (whichever is less frequent) the
thermometer should be spot-checked.  For full details of thermometer verification, please refer to API MPMS
Chapter 7.1

Mercury-in-Glass Thermometers
Glass stem thermometers should be verified for accuracy before initial use and at least once a year thereafter. In
addition before each use or once a day (whichever is less frequent) the thermometer should be field checked by
visually checking the glass capillary for breakage and separation of the mercury column.  Glass stem
thermometers with abnormally worn etched faces or broken mercury column should not be used.  If the column is
rejoined, it may be used provided that it successfully passes a bench inspection.  For additional technical details
see API MPMS Chapter 7.1.

Portable Electronic Thermometers (PETs)

Before initial use, and at least once a year thereafter, all electronic thermometers shall be re-standardized in a
laboratory or other qualified facility.  For full details see API MPMS Chapter 7.3.  In addition before each use, or
once a day (whichever is less frequent), PETs should be spot-checked by comparing the ambient reading against
an ASTM glass stem thermometer in liquid.  If the readings differ by more than 1°F or 0.5°C, the PET should be
re-standardized before it is used for custody transfer.  For details on verification of the PET see API MPMS
Chapter 7.3.

Open Temperature Measurement Procedures

Manual temperature measurement is the determination of the temperature of a liquid in a vessel's tank, using the
appropriate devices. The primary considerations of accurately determining temperature are

a. the size and location of cargo tanks,

b. whether or not heat has been applied to the cargo,
c. the atmospheric and seawater temperatures, and
d. the degree of temperature stratification within the cargo. Temperatures should be taken and should be
clearly designated as degrees Fahrenheit or Celsius, as appropriate.

Temperatures should be determined at the same time gauging is performed.  Temperatures should be taken in all
tanks, and upper, middle, and lower temperatures should be taken in each tank whenever the liquid level is
greater than 10 feet (3 metres).  For vessel tanks with less than 5000 barrels (795 cubic metres), a single
temperature measurement at the middle of the liquid will suffice (see Table 4).  The total vessel volume should be
corrected to the standard temperature on a tank-by-tank basis, using the average temperature determined for
each tank.  By agreement of all parties involved, more or less than three temperatures may be taken to calculate
an average tank temperature.

It may be noted that when temperature differentials greater than 5°F (3°C) are found, additional temperatures
should be taken.  The number of additional temperatures will vary with the temperature differential.  However,
they must always be equally spaced and averaged accordingly.

The immersion time required for the thermometer reading to reach equilibrium will vary depending on the type of
liquid and equipment.  For more specific guidelines on immersion times, see Tables 5a and 5b and refer to API
MPMS Chapters 7.1 and 7.3.

Portable Electronic Thermometers (PETs)

In addition to the steps described earlier, the following procedure is recommended for measuring temperatures
with a portable electronic thermometer (PET):

a. Attach an electrical ground between the thermometer and the tank before the hatch is opened. Check the
ground to ensure that it is securely attached to the thermometer.
b. Set the temperature range selector as appropriate.
c. Lower the sensing probe to the predetermined level.
 d. Raise and lower the probe 1 foot (0.3 metre) above and below the predetermined level to allow rapid
stabilization.
e. After stabilization, read and record individual temperatures to the nearest 0.1°F or 0.°C,
f. Determine the average tank temperature to a tenth of a degree.
g. Round off and report the average tank temperature in accordance with the most recent edition of API
MPMS round off and report average tank temperature to 1°F or 0.5°C  [round 0.5°F up]. Temperatures
may be reported in units less than whole degrees by mutual agreement.

If the probe is allowed to remain stationary, contact with a convection current of colder oil will cause low readings.
With a moving probe, however, the thermometer may be considered stabilized if the readout varies by no more
than 0.2°F (0.1°C) for 30 seconds.

Mercury Thermometers In addition to the steps described earlier, the following procedure is recommended for
measuring temperatures with a mercury thermometer.

a. Lower the thermometer assembly through the gauge hatch to the required level.
b. Repeatedly raise and lower the thermometer 1 foot (0.3 meter) above and below the required level so that
the equilibrium temperature will be reached more rapidly.
c. Withdraw the thermometer after the required immersion time.
d. Round off and report the average tank temperature in accordance with the most recent edition of API
MPMS Chapter 7.1 (round off and report average tank temperature to 1°F or 0.5°C  [round 0.5°F up]).
Temperatures may be reported in units less than whole degrees by mutual agreement.
e. Report the temperature to the nearest 1°F or 0.5°C.
f. Repeat items a through e for every tank to be 'temperatured'
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9
Principal terms used

Total observed volume

(TOV) – total volume of material measured in the tank including

cargo (oil), free water (FW), entrained sediment and water (S&W), sediment and scale as

measured at ambient (observed) temperature and pressure.

Free water

(FW) – water layer existing as a separate phase, normally detected by water

paste or interface detector and usually settled at the bottom of the tank (depending on

relative density of cargo).

Gross observed volume

(GOV) – TOV less FW and bottom sediment, being the measured

volume of oil and S&W at observed temperature and pressure. In practice, GOV is usually

calculated with no deduction for bottom sediment, which is very diffcult to quantify.

Gross standard volume

(GSV) – measured volume of oil and S&W at standard conditions

of 15°C and atmospheric pressure. In practice, the GSV is the GOV multiplied by the
volume correction factor (VCF) obtained from the appropriate ASTM/IP

Petroleum

Measurement Tables

(see next section). The GSV is the primary quantity measured and

reported on tankers.

Sediment & water

(S&W) – entrained material within the oil bulk, including solid

particles and dispersed water. Sometimes known as base sediment and water (BS&W).

Net standard volume

(NSV) – normally applicable to crude oil, NSV is the GSV minus

S&W, being a measurement of the ‘dry’ oil quantity at standard conditions. For products,

S&W is not normally deducted and is included (where appropriate) within the receiver’s

quality specifcations. Whereas samples of crude and product are commonly drawn from

ship’s tanks after loading (and before discharge), the measured S&W is not advised in time

for ship’s offcers to calculate the NSV on board.

Total calculated volume

(TCV) – total amount of oil, FW and S&W reported at standard

temperature. In practice, TCV is the GSV plus the measured FW.

For crude cargoes, claims for shortage are invariably presented in terms of net standard

volume (NSV). Therefore, if the free and entrained water content is understated at load

port, the receivers will apparently receive more water than was loaded and this may give rise

to a corresponding ‘apparent’ shortage. It should be noted that the loss statistics published

by the Energy Institute demonstrate that the difference between the mean GSV and NSV

is globally of the order 0.04 %. This provides an indication of the apparent losses arising due

to understatement of water at the point of loading. Some of this increase in water is due to

the inevitable retention of tank wash water and/or heavy weather ballast in the cargo system

prior to loading, though this is only considered to be a relatively minor factor.

For products, especially the lighter distillates, claims for short delivery are typically

presented in terms of GSV.

CALCULATION OF CARGO QUANTITIES

Calculation of the amount of oil within a ship’s cargo tanks is a straightforward procedure.

Using a pre-determined temperature and the advised density, the volume correction factor

(VCF) is readily determined from the

American Society for Testing Materials (ASTM)

and

Institute of Petroleum (IP)

Petroleum Measurement Tables.

The GOV is multiplied by the VCF

to obtain the required GSV. Depending on the units in use, the VCF will standardise the oil

volume to 15°C (m
3

) or 60°F (US barrels). For most applications, ASTM/IP tables 6, 24 and

54 are utilised to establish the VCF for a given density and temperature. Each of the tables is

produced in three versions.

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