Draft Survey: Procedures and Calculation

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draft survey Draft Survey: Procedures and Calculation

Finally, I have comfort time to complete this post after having busy with some surveys that I should fulfil. Any terms on this post should be referred to previous post Draft Survey: Terms of Conduct.

The Draft Survey procedures and calculation ascertained as the following series :

  1. Reading the draftmark of the ship, which consist of six (6) points of draftmarks, i.e.; Fore, Midship, and After at both sides of the ship,
  2. Sampling and testing the sea water or dock water density at the place where the vessel floats,
  3. Determining of deductible weights by measuring and sounding of ballast tanks, fuel oil, fresh water that existing onboard at the time of survey,
  4. Using Hydrostatic Table provided onboard to calculation.

Reading the Draftmark of the ship

Commonly, all ship are designed with draftmark for working with Draft Survey to determined their actual weight. The draftmark could be find at six (6) points on the below places:

  • Forward Port Side (FP),
  • Forward Starboard Side (FS),
  • Midship Port Side (MP),
  • Midship Starboard Side (MS),
  • Aftward Port Side (AP),
  • Aftward Starboard Side (AS),

View the Draftmark:

draft Draft Survey: Procedures and Calculation

Use the small boat to go around the ship and get as near as possible to the draft mark for best viewing. The surveyor should be read all above marks clearly, because reading the draftmark is the first and most essential process. I am not saying that other processses is not essensial, but this process is hard to do and involves many rules of conduct to gain the correctness and accuracy of Draft Survey itself (I will post it later). The draftmark read is recorded on the surveyor notebook, do not try to remember it or write down in your palm hand. Its useless and un-professional.

Sampling and testing the sea water or dock water density

After reading the draftmark, directly engage with the sampling of sea water or river water around the ship’s dock.  Why? Because the ship draft will not be the same at different water densities (at the lower density means the ship more sink and at the higher density means the ship more float).  Where as the water density is subject to changes which follow with water tide that carrying different water salinity and temperature on to the ship dock. The sea water density is indeed at density 1.025 and the fresh water at density 1.000. To determine the density of water, we need the instrument named Hydrometer or Density Meter. Inserted the Hygrometer on to the water sample on the Sampling Can or Tube, then we could check the scale pointed on the surface of the sampling water. Records the water dock density as survey data.

Determining of deductible weights by measuring and sounding

Deductible Weight could measure by sounding  the tanks which used the Sounding Tape or gauging the tank level by visual inspection. Any deductible weight such as Ballast Water, Fresh Water, Fuel and Diesel Oil, and Bilges is notify to check. Records all in the survey book includes with the density for Ballast and Bilges, and for Oil complete it with density and temperature . The Fresh Water was at density 1.000.

View the Sounding Pipe:

Draft Survey: Procedures and Calculation

Using Hydrostatic Table provided onboard to begin calculation,

I think all necessary data was completed, so we could do calculation. The calculation is uses Displacement Table or usually called Hydrostatic Table. This table is included all data that we need to complete the calculation.

  • Raw Draft Calculation; Fore Mean or Fm = (FP+FS)/2, Mid Mean or Mm = (MP+MS)/2, and Fore Mean or Am = (AP+AS)/2. while Apparent Trim  or AT = Am – Fm. the Apparent Trim is the Trim that visually find.
  • Draftmark posision and correction to perpendicular. As the ship draftmark is not placed at the perpendicular, the Fore and After draft should be corrected with distance from the draftmark to perpendicular. The correction rules is: if the Trim by Stern, the Fore correction should be minus and After correction plus, and if the Trim by Head (stem), the Fore correction should be plus and After correction minus. The Midship correction is parallel with the fore correction with the same pattern. Some Hydrostatic table provided with these correction result. But if not the reference pattern is  for Fore Correction or Fc = (Fd x AT) : LBM and After Correction or Ac = (Ad x AT) / LBM. Where Fd = Fore distance to perpendicular, Ad = After distance to perpendicular, and LBM = Length Between Mark or Length between Fore and After draftmarks  or LBM = LBP – (Fd + Ad).
  • True Draft Calculation / Draft Corrected; Fore draft corrected or Fcd = Fm + Fc, Mid draft corrected or Mcd = Mm + Mc, and After draft corrected or Acd = Am + Ac.
  • True Trim or TT : Actual  Ship Trim after draft corrected or  TT = Acd – Fcd.
  • Fore and After Mean Draft or FAm = (Fcd + Acd)/2, Mean of Mean Draft or MM = (FAm + Mcd)/2, and Mean of Mean of Mean Draft  or MMM or Quarter Mean = (MM + Mcd)/2.
  • The above calculation is similar with : MMM = {(Fcd x 1) + (Acd x 1) + (Mcd x 6)}/8.
  • Coresponding to the MMM or Quarter Mean result, the surveyor could check the value of needed parameters on Hysdrostatic table like; Displacement, TPC, LCF, and MTC. Records them accurately.
  • Get the Displacement or Disp.
  • First Trim Correction or FTc = (TT x LCF x TPC x 100) / LBP. Could be plus or minus depend on LCF.
  • Second Trim Correction STc = (TT x TT x MTC x 50) / LBP. The result always plus (+).
  • Displacement corrected by Trim or DispT = D – (FTc + STc).
  • Density Correction or Denc = DispT x {(Aden – 1.025) / 1.025}. where the Aden is Actual Density that surveyor has taken sampling and testing previously. The density correction commonly in minus (-), due to the Actual Density is usually lower than 1.025 (fresh sea water). In case of at some port where the water salinity is high, the density correction could be plus (+).
  • And we have got the Displacement corrected by Density or DispDenc = DispT + Denc. (after corrected by density we will get the actual ship weight as per shown by Draft Survey)
  • Deductible Calculation. The same as draft, the deductible also need to corresponding to the table that named Tank Table / Tank Capacity Table. Refer to the sounding records that done before, the surveyor could be calculate the total deductbile existing onboard. Total Deductible or Deduct =  Ballast Water + Fresh Water + Bilges + Fuel Oil + Diesel Oil,  this total should be minus to the Displacement corected by Density.
  • The Net Displacement or NDisp = DispDenc – Deduct.
  • The Net Displacement is the actual ship weight after minus with deductible weight. For Unloading, to estimate the quantity of cargo onboard, the Net displacement should be minus with Light Ship and Constant.

I think difficult for the amateur writer like me to describe the complex narration of draft survey calculation, but to make it clear, the sample of Draft Survey Calculation will be post sooner or later.. :)

You could try the calculation software 7s-DraftSurvey (Password: 123456)
Download at http://sevensurveyor.com/x2323l/dlall/Trial_Draft_Survey_Software.rar

Regards,
Surveyors

118 thoughts on “Draft Survey: Procedures and Calculation”

  1. Dear Capt. Michael,

    thanks for your advice.

    As my experience, reading the mid draft mark is more easy and accurate than we do measuring / sounding the freeboard. the sea water swell and bad current disturbances are the most affecting factor of sounding / measuring the freeboard.

    Regards,
    Surveyors

  2. Dear Captain,

    Thank for your interest in my new Draft Survey program, which is backed by my longtime draft surveying experience. Presently, I am testing it and shortly I should have a Demo version on my web-site available for download. I will let you know when it’s ready for download.
    You are doing a good job giving people very valuable advises regarding draft survey. However, I do not see anybody talking about taking a freeboard to obtain midship draft. As we know draft marks are not certified and the midship draft is the most important one in draft survey.

    Best regards,

    Capt. Michael

  3. Dear Capt. Michael,

    thanks for your valuable information.

    hope you could give the trial version of software for the surveyor around here to test.

    Regards,
    Surveyors

  5. Dear Ian,

    suggested to use the following:

    - Expect to read the Draft maximum sea vessels, although it is not possible or dangerous.
    - In circumstances like this, read the Draft and land next to the sea with the help of manometer, consisting of clear plastic hose, strong, mounted on both ends of the pipe to facilitate water level measurements.
    - If possible, pipes installed along the width of the entire ship – the size is taken from the overall width.
    - Reading Draft sea side obtained through adding to or subtracting from the land side of the manometer readings
    - The surface is measured from the same base line and taken to the same distance from both sides of the ship’s centerline.
    - All air must be expelled from the hose and the pipe surface is maintained at a higher elevation than the deck on the centerline.
    - The height of the water surface on both sides of the ship measured above deckline (h) or other fixed surface. The difference between the height divided by two and the result (d) is added to or subtracted from the readings Draft one to get the mean on Draft centerline.

    SAMPLE OF CALCULATION
    - QUESTION:
    Draft midships left = 8.00M, the right side of the manometer readings 8.50M on both sides of centerline.
    Full width of the ship = 20.85m. Draft midships Calculate the mean, the centerline Draft, if the difference between the 2 readings manometer manometer readings higher right = 25cm.

    - ANSWER: The width of effective 8:50 x 2 = 17.00M, with the triangle at 0:25: 17 = d: 20.85
    d = 20.85×0.25: 17 = 0.307m wide differences in management.
    Differences half-width = 0307: 2 = 0.153m. Centerline Draft = 0153 8:00 = 8.153m

    DRAUGHT SURVEY
    THE U.K. VERSION, 1994

  6. can you give me the formula for calculating the draft of a ship if :
    i can only read the draft on the shore side;
    considering the list at the time of reading draft;
    i need to find the draft in the sea side:

    e.g. actual draft reading on stbd side midship is 18.00m
    a list on stbd side of 0.5 degress.
    what will be the drafts on port side midship

    ian carolino

  7. i want to find the simplest way to calculate overall cargo of ship (coal , agri, liquid ) and also want planning for stocking of container in a vessel

  9. Dear Muhammad,

    1st trim correction : (TT x TPC x LCF x 100) / LBP
    2st trim correction : (TT x TT MTC x 50) / LBP

    TT = true trim = trim after corrected to distance of perpendiculars.

    Just try it now.

    Regards,
    Surveyors

  10. Hi Nisay,

    There are many ways to learn, you could find the one which suitable for you. For me, practice is the best teacher.

    Regards,
    Surveyors

  11. Dear Marian,

    Draft survey for all ship are use the same procedures and calculations.
    Please refer to draft survey posts and donwload the available materials on this blog.

    If you find any disputes, you could drop the comments.

    Regards

    Regards,
    Surveyors

  13. Dear sir,
    Here below is the dimension of the Hopper barge

    LENGTH OVERALL : 32.5 MTS”
    BREADTH : 7.3 mts”
    DEPTH : 2.5 MTS”
    G. R. T. : 182.33 TONS
    NO. OF OPENINGS : 04

    Please advice what would be the volume of the hopper barge,
    the cubic capacity of loading the silt from the ocean bed.
    Awaiting your reply ASAP.
    Regards

  14. Dear Faisal,

    please guide me and post simple way to calculate Trim correction.

    I’ve always making mistakes when do trim correction manually.

    special with different type of vessel sounding tables.

    Thank you so much.

    May ALLAH bless you

  15. dear sir

    I AM DOCUMENTATION PERSON OUR OFFICE PEOPLE PUT ME AS A TRAINEE IN OPERATION SECTION.

    I WANT ABOUT KNOW BERTHING DRAFT OF CAR CARRIER AND PROJECT SHIP
    HOW TO CHECK THE DRAFT PLEASE TELL ME
    REGARDS
    SATHISH KUMAR

  16. Hi, I’m a student and I have to do a final essay about draft measurement/reading installation on a containership, and the problem is that I can’t find any information on this installation. If you can help me with some information I would be very grateful. I expect your email. thank you very much

  17. I’m a young surveyor,i realy want to be a proffesional in draft surveyor. Pls,is there any material to consult that will be a directive medium for me? I need your reply, thanks.

  18. hello all

    i am a surveyor for many years but never learned to take a draft

    i want to learn it what is the best way????

    thanks greets from holland

  19. hallo,
    sometime, in my job, i have to make delivery to the barges and all time i hyre to draft surveyors – much better on F 6 or F8.
    pls i can get legal procedure for calculate the quant. on iland water ship draft survey?
    tks and compliments

  21. Dear Surveyor,

    1- can u please let me known, how many meters are required for sampling water which are used for density.
    2- where come from the water which are used for hose test.

    thanks in advance for some explanation.

    regards

    Alberto Machenera
    Beira , Mozambique

  22. Dear Beny,

    Thanks for your comments.

    The draft survey calculation is applicable for the bulk barge as well. During my experience, the barge calculation is more simple than the ship. But the basic and reference are the same. In some barges, they dont have the midship draft, and fore-aft distance to perpendiculars. It is easier to make calculation.

    Regards,
    Surveyors

  23. Dear Mr Surveyors.

    at first, thanks for your information about this posting its so helpful for me.
    this calculation may applicate on draft coal bulk barge or there is have own calculated?

    Regards

    Beny

  24. Pingback: Draft Survey Software | Marine and Cargo Surveyors

  25. AS-SALAM ALAEKUN MR FAISAL.I AM A STUDENT THAT IS NEW TO CARGO MARINE SURVEYOR AND I NEED YOUR HELP IN TERM RESEARCH SITE AND EBOOK PLS YOU CAN FORWARD THEM TO MY E-MAIL THANKS

  26. Pingback: Draft Survey: Terms of Conduct | Marine and Cargo Surveyors

  27. Can someone explain to me how do I find the:
    1. Distance of forward marks from forward PP;
    2. Distance of midship marks from midship;
    3. Distance of aft marks from aft PP;
    And most importing when we put the positive (+) and negative (-) sign.

  28. Dear Giri,

    Read it carefully, and discuss it with your surveyor friend.

    Regards,
    Surveyors

  29. Hi Lars,

    Very good question. If have time, I will try to post it soon.

    Regards,
    Surveyors

  30. Dear Nielzkie,

    In this blog there are some post about draft survey, you could check it for your references.

    Regards,
    Surveyors

  32. Srs,
    Venho pedir – lhes mais esclarecimento sobre MTC e suas considerações.

  34. can i do the short term course on DARFT Survey from Indian instute. If yes, from where ?

  35. i need a draft measuring device for ship draft survey. from where i can purchase it.
    please let me know.

  36. kindly outline for me the most technical procedure of calculating the volume gas in a ship gas tank or static layed tank.
    thanks for your expected response.

  37. Dear Sir,

    Good day to you…what are the formula on finding Draft survey..
    Hope you can reply me with the formula’s

    Ty…….so much…

  39. Good afternoon Surveyors

    Please advise where I can get formulas for calculating theoretical values of
    1.Length between perpendiculars
    2.Dipslacement based on dwt or GRT or NRT along with length, beam and draft

    I need the formulaes for different types of vessels ranging from very small boats to VLCC. I need it for rubber fender design.

    Kindly assist.

  40. Hi Rahul,

    Please make it specific, what is the formula you mean? what calculation do you wanna do?

    Regards,
    Surveyors

  41. Dear Ferdhy,

    First way:
    - You have to read 12 (twelve) times when the swell showing the high and the low levels.
    - From the above reading you have to eliminate 2 readings (1 of the highest level and 1 of the lowest level)
    - Take 10 readings which you have to then make an average by divided to 10.
    - The result gained is the best draft that near to the actual draft.

    Second way
    It is recommended to use the Draft Measuring Equipment. A measuring device may to be use to improve the accuracy of draft measurement. Such device are based on the principle that the turbulence on the surface of the water does not extend down to any great depth. they use a long, flexible, open ended, weighted hose projecting downwards to below the turbulence.

    Regards,
    Surveyors

  44. Pingback: Draft Survey: The Accuracy and Factors Effecting | Marine and Cargo Surveyors

  45. Dear Anatoly,

    I have no formula that you meant.

    The trim factor is made for trim correction at Forward, Mid, and Aft. These correction applied at the mean draft to obtain the corrected mean draft.

    Regards,
    Surveyors

  46. Dear Anatoly,

    I have no formula that you meant.

    The trim factor is made for trim correction at Forward, Mid, and Aft. These correction applied at the mean draft to obtain the corrected mean draft.

    Regards,
    Surveyors

  47. Captaouf,

    Yes you could do it. The Draft Survey is possible for any conditions you meant.

    Regards,
    Surveyors

  48. Hi George,

    Thanks for your questions. As long as I know, the ship tank table is made calibrate with the trim (apparent trim). So, we have to refer to these trim.
    In the other hand, if you find any information from the ship that the table is made refer to actual trim, you should use the actual one.

    Please remind me if any issues regards this.

    Regards,
    Surveyors

  49. Good Day,
    Sometimes there is no LCF mentioned in ship’s hydrostatic tables, but there are “trim factor fwd” and “trim factor aft”. There is a formula to get LCF using both trim factors and LBP. Mr. Surveyor, do you have the formula?

    Thanks for help.
    Anatoly.

  51. Dear Surveyors!

    Have one question.
    When we calculate the draft survey we use corrected trim (after correcting for distances of draft marks from perpendiculars) to enter the hydrostatic tables and ballast tables. So it used corrected trim to look at ballast tables with trim corrections.

    However when everybody calculates the bunkers in fuel oil tanks or mdo tanks at time of bunker survey everybody use simply d.aft-d.frw so called apparent trim. I mean that all chief engineers and surveyors I have seen so far use apparent trim to enter the capacity tables with trim for bunker tanks.

    Why it so and is it a correct way?
    Will be appreciated to hear any comments.

    Bat rgds
    George

  53. Dear Traore,

    Ballast calculation is simple, you could obtain by the following steps:
    - sounding the tank,
    - taken the ballast water density,
    - check the cubic quantity on the ship ballast tank table,
    - and calculate the Metric Ton quantity.

    For example :
    - Sounding of tank DBT 1 P : 5.35 M,
    - Ballast Water Density : 1.020,
    - Cubic quantity on table at 5.35 M = 368.120 Cubic Meters,
    - Metric Ton quantity = 368.120 x 1.020 = 375.482.

    Best Regards,
    Surveyors

  54. Dear Nitin,

    You could refer to the Loading Manual Book that provided onboard the vessel.

    Regards,
    Surveyors

  55. dear captian, could you please send me the procedure and methods of surveying one unit of the propulsion plant of a ship. i am a cadet of maritime academy of Nigeria.

  56. thank you for draft survey explanation.
    can you explain us how to make calculation on ballast?
    best regards

  57. Dear Sir,
    For bulker vessels ,could you pls. indicate any thumb rule OR
    Empirical formulae,that based on draft,how can we ascertain
    the cargo weight which can be loaded in the vessel.The range may
    be taken from Cargo load of 7000 MT up to 15000 MT.

  59. I see this brief very useful to me to figure out steps to calculate the draft survey.Thanks!

  60. Dear Mcdudz,

    The Draft Survey formula has considered to deflection correction, due to it was made up to the Quartermean (Mean of Mean of Mean – MMM), meanwhile the deflection correction is applied at the Mean Draft. The calculation result is the same for both methods.

    Example (briefly, the calculation is directly to corrected draft):

    Fcd = 2.232
    Acd = 2.851
    Mcd = 2.502
    FAm = 2.542

    1. For Draft Survey Formula :
    - MM = (FAm + Mcd) / 2 = 2.522
    - MMM = (MM + Mcd) / 2 = 2.512 (use to check corresponding displacement at table)

    2. For Deflection correction:
    - FAm = 2.542
    - Hogging = 2.502 – 2.542 = -0.040 (Deflection or D)
    - Equivalent Draft = FAm + 3/4 D = 2.542 + (3/4 x -0.040) = 2.542 + (-0.030) = 2.512

    For any abbreviations, you could refer to my late posts. Please advice me whether any mistakes.

    Regards,
    Surveyors

  61. Dear Santoso,

    Thanks, there no simple formula for Draft Survey. The Formula that I have inserted on my previous posts, as commonly use on the Ship’s Draft Survey.

    Regards,
    Surveyors

  62. Dear sir,

    I have respect for you explain any proble darft survey.
    Can you give me a simple formula to calculate cargo on boat with draft survey?
    Thanks for your answer.

    Regards.
    Practicips

  63. Good day, I have some queries also, pls advise if the deflection correction are still aplicable now a days? As I look some draft survey reports, programs, the deflection correction is not found or applied. As you know in big ship’s specially more than 80,000 dwt, the deflection correction is big. Pls advise also your calculation in deflection correction if you have.

  64. Dear Khan,

    You can drop your question, comment or feedback on this website, due to I am rarely check my mail. My mail address is faisal.yusuf(at)live.com.

    Regards,
    Surveyors

  65. Dear Sir

    What is your email address? I tried to post my questions 3 times but seem like it go no where. Thanks.

    Regards

  66. Hi Luis,

    I have ever found the same case like yours. The best you can do is find the terms on Hydrostatic Table that you working with. Usually in the first page you will find it.

    When the first time meeting with this case, I am very confusing. I try to guess the LCF, and reopen the Hydostactic Table many times but nil. Then.. I asked the Chief Officer about it. Unfortunately he did not know because he is the new Chief Officer and doing calculate with the Loading Manual on Ship’s Computer. Or he wanna test the surveyor at the time :)

    In the end, I reopened the data page and rechecked the Terms :

    LBP = Length between Perpendicular
    MTC = Moment to ChangeTrim at 1 cm.
    etc.. etc. then I found
    LCA = LCF (Longitudinal Center of Floatation)
    That the answer.. So, I back to the table and checked the LCA and written down as LCF.
    In the case, you may also find LCB = LCF.

    It is recommended for surveyor to check the terms and the calculation rules that provided on the Hydrostatic Table prior doing calculate. If you are in doubt, please asking for the Original Hydrostatic (in blue printing) from the ship to get the correct information and calculation.

    Regards,
    Surveyors

  67. Dear Sir.

    In some vessels I have found that no information about LCF is vailable in the Hydrostatic tables, all the others are except LCF. Unfortunately no cross curves were available, no more ship’s info available also

    There is some way to calculate the LCF value??

    Appreciatte in advance your answer.

    Luis

  68. Dear Surveyor can u pl mail me what is the procedure to calculate draft of Petroleum Tanker / vessel and oil tanker / vessel

  69. Hi Tamim,

    Terimakasih untuk komentarnya..

    Mungkin kamu belum begitu familiar dengan istilah perkapalan. Atau kalau bahasa yang menjadi kendala, kamu bisa kopi artikel nya dan terjemahkan di http://translate.google.com/#.

    Ada juga Training Draft Survey yang diadakan oleh Asosiasi Independent Surveyor Indonesia (AISI) coba check di http://www.aisi-indonesia.org.

    Salam,
    Surveyors

  70. Hi Feras,

    Please clarify what does “the vessel is half loaded but yet above zero” means? So, I could try to find the answer. Thanks.

    Best Regards,
    Surveyors

  71. dir pak surveyor,
    terima kasih atas artikel bapak ini, saya tertarik ingin mempelajari draught survey
    tapi, saya bingung untuk mempelajarinya, karena ada istilah yang tidak saya mengerti dan perhitungannya
    saya harap bpk mw memberi penjelasan tentang draught survey, istilah yang sering d gunakan dan contoh perhitungannya

  72. dear sir,
    my question is: regarding the lcf sign as to be applied for the formula used to calculate the first trim correction. what sign does the LCF get if it is reducing.i.e the vessel is half loaded but yet above zero!? is it minus or plus???
    very urgent reply required

  73. Waalaikum Salam..

    Me in my best, thanks.

    Draft Mark reading is the essential part of Draft Survey, where the Draft Survey is begin from the reading part. There are some rules to get the best result. Actually it should be write down in one posting, but the basics are :
    - Read the Draft Marks as close as possible,
    - Use the small boat to read close the Draft Marks, do not see it from the ship’s maindeck,
    - Vessel is secured at the wharf properly,
    - No any ship’s gears movement allowed at the time, (such as crane, derrick etc),
    - No any ship’s liquids transfer activity allowed during reading, (ballast, fresh water, fuel and diesel oil),
    - Find the draft in meter first then continue with centimeter to prevent big error.
    - For the heavy swell sea condition it is recommended to read and record 12 times, taken out 1 biggest and 1 smallest of the reading results, and make avarage draft from the 10 results remained.

    Trying to post this as complete version soon.

    Second one, you could check my last post Draft Survey : Terms of Conduct for Light Ship and Constant Terms.

    Regards,
    Surveyors

  74. Dear Joe,

    Fisrt, the Density Correction is the correction for water mass weight. Commonly, the Ship Hydrostatic Table is makes at Sea Water Density (1.025). As the ship is floating on the sea water or river water that may have different densities, it shoud be applied density correction to gain the actual weight.

    There is no relation between Density Correction to Ship Light Ship and Constant.

    Regards,
    Surveyors

  75. Dir Sirs,

    I’m new in this field of surveying and I was hoping if you could clarify the following;

    Displ Corrected for trim – Actual Displ = Density correction.

    Q: What’s the significance of ‘density correction’ and also is there a relation between Density Correction and the Ships lightship constant.Would greatly appreciate your expect advice and answers.

    Kind Regards
    Joe TOVA

  76. Assalamoalykom
    Dear Faisel
    how r u, I read your data related to draft survey which is very helpful for me and i learn manay thinks which I not know abt. I am First time asking to you some questions my 1st question is that plz can you Expalan that which kind of Ruls are involved to Record Draft Marks (You said abt that you will post later) and my 2nd question is What is light ship & Constent onboard. please if you can send me answer by mail i will very thankfull of you

    Best Regard Ejaz Khan

  77. Good day. I am a junior surveyor struggling to learn draft survey
    I would like to know the formula to calculate especially

    LBM: length between mark
    FD “ Fore distance to perpendicular:
    AD : after distance to perpendicular:
    Thank you very much indeed

  78. Dear Sir
    How do i calculate approx. draft of a newly build vessel with all deadweight on board.
    What all parameters do i need for it from stability booklet.
    Can you explain with an example.

  79. DEAR SIR,

    HIGLY APPRECIATE IF YOU SEND ME BY RETURN MAIL THE ASTM TABLE 54 FOR VCF DENSITY& TEMP CORRECTION

    TKS& RGDS

  80. Hi Mehdi,

    Thanks for comment. Appreciated you as my Senior, as I have just completed 10% surveys of yours.

    I think the data to be followed was written on the Hydrostatic Table. But if then we verify and will find that the both correction is applied trim to complete the calculation. The more trim you get the more correction will be.

    FTc is more fluctuate than STc. Its happen due to point of LCF sometimes moving to the aft and fore of Ship Centre / Midship, where it will result the LCF in Minus and Plus. The value of LCF could be down below the 1.00 like 0.15 depends on the LCF’s distance from Midship. Mathematically, you have been times 0.15 with other numbers, but certainly you do devide it. This will be influent to reduce FTc total value when you do calculate it.

    On the other hands, the MTC is not subject to minus. And the MTC value is typically the high number, means above 3.00, so it will advance for your calculation.

    Anyone has any advice? waiting for your comment.

    Regards,
    Faisal

  81. Nitin, when all the requirements in the calculation of survey based on the Draft UN / ECE Code 1990 followed, the accuracy could be expected in the limit:
    - For ship >10,000 DWT between 0.1 s / d 0.3%.
    - For ship <10,000 DWT between 0.3 s / d 0.6%.

    In fact the practice of this ideal condition can rarely be achieved minimum range within the limits 0.5% of the total weight.
    When the technique is still less true implementation, the deviation can be achieved up to 1%.

    Here the experience and skill of surveyor are involved.

    Regards,
    Faisal

  82. Dear Nitin,

    Thanks, the Specimen of Calculation on the post is made for initial survey, when the ship arrive at discharge port. In the next steps, the surveyor need to carry out the final draft survey in the same way when the ship has completed discharge her cargo.

    The initial survey Net displacement that deducting / minus with the final survey Net Dispalcement will show you the total amount of cargo discharge from the mentioned ship.

    Regards,
    Faisal

  84. PLs. explain me the total draft survey of a dry bulk vessel with detailed calculations .Pls. use one illustrative example and make use of figures,

  85. Hi Nick,

    Thanks, as known the correction is applied from the draft mark location. You could refer it to the Fore and Aft Distance on Hydrostatic Table that provided by the ship and compare with your draft reading place.

    As my experience, the draft at the Aft on the flat of stern that usually found in the container ship is additional draft for reference only. You should check the port and starboard draft at stern for your draft survey.

    Regards,
    Faisal

  86. Hi Herah..

    Thanks for your questions.

    Refer to your first question, I will post soon: how to calculate ship bunker.

    The second: For SG 0.9900 is included on 0.8595 to 0.9245 with Correction Factor Per Degree Celcius at 0.00065.

    Regards.
    Faisal

  87. Pls advise if the draft marks aft are on the flat of the stern and on the after end of the rudder need any correction or not. I see many containerships with the draft marks aft on the flat of the stern.

  88. Hi Darussalam,

    Thanks for your comment. Simplify the calculation for tank sounding were as follows :
    - Sounding resulting Quantity in Cubic Meter (see on Tank Quantity Table).
    - Quantity in Cubic Meter (x) Volume Correction Factor (from ASTM Table 54B) resulting Quantity in Kiloliter @15C.
    - Quantity in Kiloliter @15C (x) Weight Correction Factor (from ASTM Table 56) resulting Quantity in Metric Ton.
    - ASTM Table 54B for VCF is gained by Oils Density @15C and Temperature.
    - The complete calculation will be posting soon. Just check the blog later.

    Regards..

  89. Sir,

    what is the coefficient factor if you have 0.9900 Specific gravity @ 15 degree celcius?

  90. Sir, plz answer this problem for calculating bunker:

    A vessel is to take a 1000 MT of IFO.Calculate correction made:SG at 15 degree celcius is 0.9900: TCF at 40 degree celcius is 0.9844:average combined SG+TCF is 0.9700.

    Can you answer this problem ?

  91. Dear colleuges I have done almost 3000 attendances on vessels for draft survey..one thing which I still am thinking about and not found answer is in some cases the second trim correction was larger than FTC ..? Why

    warm regrads
    mehdi

  92. dear sir,
    thanks for the information… can you give me a simple calculation for tank sounding for bunker??
    Regards Darus,

  93. Dear Ariz,

    Thanks for comments. The above formula you have submitted is not correct. You’d better to check it, maybe you misplace the elements.

    Regards,
    Faisal

  94. Let ROB = x

    A – B / C – B = x – D / E -D

    (A-B/C-B)+D = x / (E-D)

    (A-B/C-B)+D
    ____________ = x
    (E-D)

  95. is there any shortcut for the interpolation method shown above? I know my professor taught us but coudn’t remember.

    thanks
    Aris

  97. Hello, Sir,

    I am also surveyor too, i want to know what is the MCTC and way they uses during draft calculation LCF and MCTC, kindly give me reply,

    thanks,

  98. Dear Ashveer,

    Thanks for comment. Please take a look the sample of Interpolation on my post Draft Survey: Specimen of Calculation.
    I think there is no formula or easy method likes you meant. Because we should consider the unique shape of the ship to make calculation for Draft Survey (except for box shape vessel).

  99. Good day. I am a junior surveyor struggling to learn interpolation . Is there a formula or do you have an easy method for calculating the weight using the true trim that is not on the hydrostatic table eg. T1 given t3 given calculate weight found t2 between given trims for a specific sounding. Really would appreciate your help

  101. I use this correction formula for ballast tanks:
    A=S-Trim*Ltank/(2*LBP)
    A – Adjusted Sounding at Aft Bulkhead Tank
    S – Actual Sounding
    Ltank – length of the tank
    Trim – vessel’s trim(+ to aft, – to fore)
    LBP – length between perpendiculars
    So after getting A, refers it to the Tank Capacity Table to find the quantity on Tank.
    This formula can be used only when the tanks have a almost paralelipipedic shape (no way to be used for forepeak and afterpeak).
    If the vessel has no correction tables for ballast tanks is advisable to ask that the vessel to be put on even keel(if is safe).
    Mr. “surveyors”
    Your formula show more ballast water in tank when vessel’s trim is to aft, which is not true.

  102. Dear Sir,
    i was wondering if you could post any example of procedure in draft survey on calculating the ballast considering trim and when ballast in cargo hold corrections for add. height when measuring from top. Also procedure when calculating fuel.

    Regards,
    student

  103. Thanks Suhendar,

    The Draft Survey and Shore Scale / Weight Scale were the same function to determine quantity of cargo. as long as I known there is no rules to arrange the percentage of differences for both techniques. Caused each Technique should be accurate. Draft Survey is depends on the Hydrostatic Table calibration, and the Scale is depends on the accuracy of calibration of unit of Scale.

    Both of them are recommended. And if the Techniques has the same accuracy, it should be resulted the same figure of weight quantity. For Bulk Cargo, it is recommended to use draft survey, because you never know how much cargo losses or spillages during discharging and conveying by truck to the Scale. The Scale is essensially uses for actual quantity received by the Receiver.

    For other readers, please submit your comments if you have got the rules as Suhendar asked for.

    Regards,
    Faisal

  105. Alex,

    You have to consider the trim of tug boat to obtain the correction of sounding that you have done, due to on tug / vessel with trim the liquid on tank were at different level between sides (fore and aft sides of tank). The correction is made to flat it on the same level (being actual liquid level) for calculation.

    As your sounding quantity still in Cubic Meter, the density of fuel oil is needed to converted the Cubic Meter to Kilo Liter, and than from Kilo Liter to Metric Ton. ASTM Table 54b (for Volume Correction Factor or VCF) and Table 56 (for Weight Correction Factor or WCF).

    Regards,
    Faisal

  106. Dear Sir,

    What if we have to consider the trim of the tugboat and the density of the fuel oil?

    Please advise.

    Regards,
    Alex

  108. Dear Capt. Valter,

    Thanks to comment.

    Although in calculation the differences of both methods (1 and 2) in small quantities as well, but it could be a question to standard of draft survey that we have to use from the our customers.

    I am in opinion that the Displacement corrected to density should be the displacement after corrected by the 1st and 2nd trim correction. By mean, the vessel displacement should be free from all vessels un-box shape and un-even keel correction before correcting by density. This method is commonly use for bulk carrier and it recorded on vessel hydrostatic table.

    The UN ECE might be mean the same, the D they meant is D after 1st and 2nd trim correction, where we mentioned as DispT.

    Waiting for your next comments. :)

    Best Regards,
    Faisal

  109. Dear sir,

    I have find discrepancy between your way to calculate density correction and UN ECE recomandations (which is used as a standard for many customers). I’m asking You for the opinion becouse we have discousssed a lot among my coleagues.

    The difference is in Displacement where by you Displacement corrected for the trim should be used, while by UN ECE standard the displacement from the table (line 161) should be used.

    1. Your way and also my opinion is the same

    Denc = DispT x {(Aden – 1.025) / 1.025}

    2. UN ECE method

    Denc = D x {(Aden – 1.025) / 1.025}

    Please tell me your opinion.

    Regards

    Capt Valter Suban, M.Sc.

  111. Hi Milind,

    - Expect to read the Draft maximum sea vessels, although it is not possible or dangerous.
    - In circumstances like this, read the Draft and land next to the sea with the help of manometer, consisting of clear plastic hose, strong, mounted on both ends of the pipe to facilitate water level measurements.
    - If possible, pipes installed along the width of the entire ship – the size is taken from the overall width.
    - Reading Draft sea side obtained through adding to or subtracting from the land side of the manometer readings
    - The surface is measured from the same base line and taken to the same distance from both sides of the ship’s centerline.
    - All air must be expelled from the hose and the pipe surface is maintained at a higher elevation than the deck on the centerline.
    - The height of the water surface on both sides of the ship measured above deckline (h) or other fixed surface. The difference between the height divided by two and the result (d) is added to or subtracted from the readings Draft one to get the mean on Draft centerline.

    SAMPLE OF CALCULATION
    - QUESTION:
    Draft midships left = 8.00M, the right side of the manometer readings 8.50M on both sides of centerline.
    Full width of the ship = 20.85m. Draft midships Calculate the mean, the centerline Draft, if the difference between the 2 readings manometer manometer readings higher right = 25cm.

    - ANSWER: The width of effective 8:50 x 2 = 17.00M, with the triangle at 0:25: 17 = d: 20.85
    d = 20.85×0.25: 17 = 0.307m wide differences in management.
    Differences half-width = 0307: 2 = 0.153m. Centerline Draft = 0153 8:00 = 8.153m

    DRAUGHT SURVEY
    THE U.K. VERSION, 1994

  112. Hi Alex,

    Thanks, you have to use interpolation to get the mentioned quantity.

    Let’s assume 2.380 = A, 2.375 = B, 2.400 = C, 26.15 = D, and 26.50 = E.

    The Formula is: ROB = D + {((A – B) / (C – B)) x (E – D)}

    As per the above formula the ROB found 26.157 m3. You can try it. :)

  113. Dear Sir,

    I would like to know the formula to calculate the remaining bunker (MGO/Fresh Water/LO/GO/DO) on board based on the tank sounding table.

    For example:
    Sounding – 2.38m
    Tank sounding table shows:
    1) 2.375 – 26.15m3
    2) 2.40 – 26.50m3
    How to get the value (ROB) at 2.38m?

    Regards,
    Alex

  114. Can some one please guide me on the procedure of calculating overside drafts of a vessel with a list and where over side drafts cannot be successfully read.

  115. Hi Myo..

    Thanks for your comments.

    As I know, there is no differences for formula between the Ship and Hopper Barge Draft Survey. Draft Survey formula is for general uses.

    For references, you could download the complete Draft Survey Standard and Procedures at this LINK

  116. Dear Sr,
    Your posted were support me to learn about Draft survey.I’m a junior surveyor in our country,Union of Myanmar at South East Asia.
    I want to request you that to explain about Draft survey for Barge carrier and Hopper calculation.Because the technique in our country were very poor to learn.I want to know the formula to calculate the water content of Sea Sand cargo.
    Regard,
    Myo

  117. Hi James, thanks for your question..

    I have made try to adopt from Petroleum Calculation named Weight Formula. The formula is as follows:

    A = S + {(U – DF) x F}
    Where :
    - A : Adjusted Sounding at Aft Bulkhead Tank
    - S : Actual Sounding
    - U : Sounding point distance to Aft Bulkhead
    - D : Total Height of Tank
    - F : Trim Factor, where the formula is Trim divided by LBP.
    - DF = D x F.

    So after getting A, refers it to the Tank Capacity Table to find the quantity on Tank.

    For example No. 2 Water Ballast Tank Portside:
    Sounding = 1.27 meters,
    U = 3.00 meters,
    D = 19.00 meters,
    Trim = 2.50 meters,
    LBP = 182.00 meters

    So we can calculate,
    F = 2.5 : 182 = 0.014 and
    DF = 19.00 x 0.014 = 0.261
    Then,
    A = 1.27 + {(2.5 – 0.261) x 0.014}
    A = 1.27 + (2.239 x 0.014)
    A = 1.27 + 0.031
    A = 1.301. (check on Tank Capacity Table).

    Does anyone has the other correction ways? I would be plesant if you could submit reply to this comment.

  118. I found your brief on draught surveys very informative. Can you advise if there is a standard correction formula for asertaining the amount of ballast in a tank where there are no trim corrections available.
    Regards,

    James Barr

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