Draft Survey: Specimen of Calculation



As I have promised you, I write down this post to explain specimen of Calculation in Draft Survey. Please also refer to the previous post Draft Survey : Procedures and Calculation.

Ok, now we could directly go to the point. The vessel has alongside at the wharf in port to discharge the grain cargo. The Ship’s Particulars shown :

Name of Vessel : MV. OCEAN BALL, – Port of Registry (POR) : Panama, – Lenght Over All (LOA) : 182.00 M, – Lenght Between Perpendiculars (LBP) : 179.00 M, – Breath (B) : 32.20 M, – Depth (D) : 17.15 M, – Gross Tonnage (GT) : 28,342 MT, – Net Tonnage (NT) : 17,664 MT, – Summer Draft (SD) : 12.163 M, – Summer Deadweight (DWT) : 52,998 MT, – Light Ship (LS) : 7,780 MT, Constant (CS) : 320 MT, – Fore Distance to Perpendicular (Fd) : 1.70 M, – After Distance to Perpendicular (Ad) : 9.45 M.  See Picture :

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The Surveyor came onboard and made Draft Survey to determine the quantity of cargo on arrival. During inspection, she’s draft marks and others data finds as the followings :
– Fore Draft Port (FP) : 10.79 M / Fore Draft Starboard (FS) : 10.81 M.
– Mid Draft Port (MP) : 10.90 M / Mid Draft Starboard (MS) : 11.03 M.
– Aft Draft Port (AP) : 11.16 M / Aft Draft Starboard (AF) : 11.19 M.
– Density of Sea Water Sample (Den) : 1.021.
– Ballast Water (BW) : 265.00 Cubic Meter at Density 1.025, – Fresh Water (FW) : 183.00 MT.
– Fuel Oil (FO) :  612.00 MT, – Diesel Oil (DO) : 161.00 MT, – Lub Oil (LO) : 29.00 MT.
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The Draft Survey Calculation is described as below :Raw Draft Calculation
– Fore Mean (Fm) = (FP + FS) / 2 = (10.79 + 10.81) / 2 = 21.60 / 2 = 10.800 M.
– Mid Mean (Mm) = (MP + MS) / 2 = (10.90 + 11.03) / 2 = 21.93 / 2 = 10.965 M.
– Aft Mean (Am) = (AP + AS) / 2 = (11.16 + 10.19) / 2 = 22.35 / 2 = 11.175 M.
– Apparent Trim (AT) = Am – Fm = 11.175 – 10.800 = 0.375 M.
– Length Between Mark (LBM) = LBP – (Fd + Ad) = 179.00 – (1.70 + 9.45)
= 167.85 M

Draft Correction to Distance to Perpendicular.
– Fore Correction (Fc) = (Fd x AT) / LBM = (1.70 x 0.375) / 167.85 = 0.003798
= 0.004 M (rounded to 3 Decimals).
– Mid Correction (Mc) = (Md x AT) / LBM = (0.00 x 0.375) / 167.85
= 0.000 M (Not Available)
– Aft Correction (Ac) = (Ad x AT) / LBM = (9.45 x 0.375) / 167.85 = 0.021112
= 0.021 M (rounded to 3 Decimals).

True Draft and True Trim
– Fore Draft Corrected (Fcd) = Fm + Fc = 10.800 + (-0.004) = 10.796 M.
– Mid Draft Corrected (Mcd) = Mm + Mc = 10.965 + 0.000 = 10.965 M.
– Aft Draft Corrected (Acd) = Am + Ac = 11.175 + 0.021 = 11.196 M.
– True Trim (TT) = Acm – Fcm = 11.196 – 10.796 = 0.400 M.

Final Draft Calculation
– Fore and Aft Mean (FAm) = (Fcd + Acd) / 2 = (10.796 + 11.196) / 2 = 21.992 /2 = 10.996 M.
– Mean of Mean Draft (MM) = (Mcd + FAm / 2) = (10.965 + 10.996) /2 = 21.961 / 2 = 10.9805 M.
– Quarter Mean (MMM) = (MM + Mcd) /2 = (10.9805 + 10.965) /2 = 21.9455 /2 = 10.97275 M.
= 10.973 M.
– Or MMM = {(Fcd x 1) + (Acd x 1) + (Mcd x 6)} / 8 = {(10.796 x 1) + (11.196 x 1) + (10.996 x 6)} / 8
= (10.796 + 11.196 + 65.790) / 8 = 87.782 / 8 = 10.97275 M = 10.973 M.
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Hydrostatic Table

Refer to the Table, we could obtain :

Displacement (Disp)
– Disp  at 10.970 M :  54,266.860 MT (DISP. FULL).
– Disp at 10.980 M :  54,321.070 MT (DISP. FULL).
– Disp at 10.973 M : 54,266.860 +[ {(10.973 – 10.970) / (10.980 – 10.970)} x (54,321.070 – 54,266.860)]
= 54,266.860 {(0.003 /0.010) x 54.210} = 54,266.86 + (0.3 x 54.210)
= 54,266.860 + 16.263 = 54,283.123 MT

Ton Per Centimeter (TPC)
– TPC  at 10.970 M :  54.210 MT (Below TPC on Table).
– TPC  at 10.980 M :  54.220 MT (Below TPC on Table).
– TPC at 10.973 M : 54.210 +[ {(10.973 – 10.970) / (10.980 – 10.970)} x (54.220 – 54.210)]
= 54.210 {(0.003 /0.010) x 0.010} = 54.210 + (0.3 x 0.010)
= 54.210 + 0.003 = 54.213 MT.

Longitudinal Centre Flotation (LCF)
– LCF  at 10.970 M :  1.180 MT (Below LCF on Table).
– LCF  at 10.980 M :  1.190 MT (Below LCF on Table).
– LCF at 10.973 M : 1.180 +[ {(10.973 – 10.970) / (10.980 – 10.970)} x (1.190 – 1.180)]
= 1.180 {(0.003 /0.010) x 0.010} = 1.180 + (0.3 x 0.010) = 1.180 + 0.003 = 1.183 M.
marine cargo ship surveyors
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Moment To Change Trim (MTC)
– MTC = MTC 1 – MTC 2.
– MTC 1 = MMM + 0.5 = 10.973 + 0.5 = 11.473 M.
– MTC 1  at 11.470 M :  709.910  (Below Table).
– MTC 1 at 11.480 M :  710.060 (Below Table).
– MTC 1 at 11.473 M : 709.910 +[ {(11.473 – 11.470) / (11.480 – 11.470)} x (710.060 – 709.910)]
= 709.910 {(0.003 / 0.010) x 0.150} = 709.910 + (0.3 x 0.450) = 709.610 + 0.045 = 709.955.marine cargo ship surveyors
– MTC 2 = MMM – 0.5 = 10.973 – 0.5 = 10.473 M.
– MTC 2  at 10.470 M :  686.460  (Below MTC on Table).
– MTC 2 at 10.480 M :  686.770 (Below MTC on Table).
– MTC 2 at 10.473 M : 686.460 +[ {(10.473 – 10.470) / (10.480 – 10.470)} x (686.770 – 686.460)]
= 686.460 {(0.003 /0.010) x 0.310} = 686.460 + (0.3 x 0.310) = 686.460 + 0.093 = 686.553.
marine cargo ship surveyors
So,  MTC = MTC 1 – MTC 2 = 709.955 – 686.553 = 23.402.
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**** From the above results, we collected the data as follows:
– Disp = 54,283.123 MT, – True Trim (TT) = 0.400 M, – LBP = 179.00 M,
– TPC = 54.213, – LCF = 1.183, – MCT = 23.402.

First Trim Correction (FTc)
– FTc = (TT x TPC x LCF x 100) / LBP =  (0.400 x 54.213 x 1.183 x 100) / 179.000
= 256.35916 / 179.00 = 14.331615 = 14.332 MT.

Second Trim Correction (STc)
– STc = (TT x TT x MTC x 50) / LBP = (0.400 x 0.400 x 23.402 x 50) / 179.000
= 185.536 / 179.00 = 1. 045899 = 1.046 MT.

Displacement Corrected to Trim (DispT)
– DispT = Disp + (FTc + STc) = 54,283.123 + (14.332 + 1.046) = 54,283.123 + 15.378
= 54,298.501 MT.

Density Correction (Denc) <
– Actual Density (ADen) = Sample Sea Water Density = 1.021
– Denc = DispT x {(ADen – 1.025) / 1.025} = 54,298.501 x {(1.021 – 1.025) / 1.025}
= 54,298.501 x (-0.004 / 1.025)
= 54,298.501 x  (-0.0039024) = -211.89947 = -211.899 MT.

Displacement Corrected to Density (DispDenc)
– DispDenc = DispT + Denc = 54,298.501 + (-211.899) = 54,086.602 MT.

Deductible Weight (Deduct)
– BW = 265.00 x 1.025 = 271. 625 MT, – FW = 183.000 MT, – FO =  612.000 MT,
– DO = 161.000 MT, – LO = 29.000 MT.
– Total Deduct = 1,256.625 MT.

Displacement Minus to Deductible Weight = Net Displacement (NDisp)
– NDisp = DispDenc – Deduct = 54,086.602 – 1,256.625 = 52,829.977 MT.

Estimated Cargo onboard (EstCOB)
– To estimated quantity cargo onboard, we need to know about Light Ship and Constant. Light Ship and Constant data is provided on the Ship’s Loading Manual. For the new ship, we could refer to the Constant on the Manual, but for the old ship it Constant may vary, please refer to the Chief Officer Constant Declaration or Draft Survey Previous Port, or we could calculate it in the final survey after the Ship completing to discharge her cargoes (empty Ship).
– Light Ship (LS) = 7,780.000 MT, – Constant (CS) = 320.000 MT.
– EstCOB = NDisp – (LS + CS) = 52,829.977 – (7,780.000 + 320.00)
= 52,829.977 – 8,100.000 = 44,729.977 MT.

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See the following Draft Survey Report Form..

marine cargo ship surveyors

 

 

 

 

 

 

 

 

 

 

 

 

 

We have completed the Initial Draft Survey, I hope it useful and see you in the next post.

Regards,
Surveyors



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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