Petroleum Calculation Series: Shipboard

marine cargo ship surveyors

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
– 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)
– 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:
– 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)
– 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
– Free water volume
– Gross Weight in air
– Oil temperature
– Suspended water (% volume) BS%W (Bottom Sediment and Water)
– API Gravity

Ship Loaded figures
– 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
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.


Author: Faisal Yusuf

Hi, my name is Faisal Yusuf, but you can call me Surveyor. I live in Jakarta, Indonesia and work as a surveyor.

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  1. Dear Sadz LV,

    Thank you. All files on the website has packed or zipped to .rar file. before installing, you should be unpacked / unzipped the files using WINRAR. if you don’t have WINRAR you could download it free at link : good luck.


  2. Sir,
    Thanks a lot for yours above, i am chief officer onboard product tankers but not familiar on crude oil, it’ll be a great help for my incoming crude oil vessel assignment. By the way, wondering what kind of file to open your “Simple Trial Software” i can’t open it with excel either, kindly advise.
    Thanks once again!

  3. Dear Pilot,

    Not limited to BBLS, buyer and seller can use LT or MT for payment, its depends on their contract / agreement.


  4. please can you guide me that why we need Long tonnes, metric Tonnes while all payment is based on BBLS.

  5. Merci pour tous ces informations qui sont très utiles

  6. You are welcome Ragu.

  7. Hi sir
    Nice work.

    Samuel K. Swaray

  8. dear sir,
    Many thanks for the above information.
    for me crude are rare (may be four survey in year) survey, i feel i can refresh through this.
    Once again thanks sir.
    B regards

  9. Hi Julius,

    Thanks for commenting. Like your motto.


  10. Hi Sir,

    Many thanks for the info of your website.

    Anyway, Current I working as marine surveyor for 6 years,sometime, need to be refresh my brick mind.

    thanks sir.


  11. Hi Park Hyun Chul,

    Thanks for your comments. Glad to hear about it.


  12. Good day ,. Sir

    I am working surveyor at Soth Korea, daesan port ,

    we administrator of Chemical product (BTX: Benzen, S.M, P.X, TOL, M.Xylene),

    Gasoline, Crude Oil, Naph, Gas(1.3BD, PGPL)

    Thanks to You , IT really great Data For Me


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