Draft Survey: The Other Side

Distance Draft Mark From Perpendiculars

marine cargo ship surveyors

The above picture show you the distance of draft mark to perpendiculars. Some of you may have finds the above arrangement. But how if you find it for the first time? How do you calculate it?

Commonly in the table for draft correction, the distance of draft mark measures to the nearest perpendiculars such as;
Distance of Aft Draft Mark to Aft Perpendicular, Distance of Mid Draft Mark to Mid Perpendicular and Distance of Forward Draft Mark to Forward Perpendicular.
But the above picture shows:
The X1 is represent the Distance of Aft Draft Mark to Aft Perpendicular. (same figure)
The X2 is represent the Distance of Mid Draft Mark to Aft Perpendicular.
The X3 is represent the Distance of Forward Draft Mark to Aft Perpendicular.

To calculate the distance for correction values for Mid and Forward Drafts, we need the LBP.

marine cargo ship surveyors

As you find the LBP on the above picture is 148.00 M, so the calculation as below:
The X1 is represent the Distance of Aft Draft Mark to Aft Perpendicular. (same figure)
The X1 = 6.10 M (X1 = dA)

The X2 is represent the Distance of Mid Draft Mark to Aft Perpendicular.
where X2 = 74.00 M.
X2 = X2 – (LBP/2)
X2 = 74.00 – 74.00
X2 = 0.00 M (X2 = dM)

The X3 is represent the Distance of Forward Draft Mark to Aft Perpendicular.
where X3 = 146.01 M.
X3 = LBP – X3
X3 = 146.01 – 148.00
X3 = 1.99 M (X3 = dF)

LCF From Aft Perpendiculars

See the below hydrostatic table, could you find the actual LCF?

marine cargo ship surveyors

In the above picture, the LCF show in Xf. where the values base on the distance of LCF itself from Aft perpendiculars.
So you could use the below formula :
What is LCF on Draft 1.60 M?
LCF 1.60 = LCF on table – (LBP/2)
LCF 1.60 = 78.46 – 74.00
LCF 1.60 = 4.46.

MTC Per Meter

How About MCT? the MTC on the above table show MTC per Meter not Per Centimeter as required for draft calculation. To obtain the actual MTC you should divide the MTC on table by 100.
What is MTC on Draft 1.70 M?
MTC 1.70 = 22556.42 / 100
MTC 1.70 = 22.55642

Drop your comment and advice to improve this post.

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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6 Comments

  1. Hi Ibrahim..

    There is no way to do, except telling ship’s reps to make forward draft of the ship immersed on the water. So, we can read the draft.

  2. hello
    thank you for this information
    but i have a questation
    ( if the bow of vessel rise up of water line ( nigative value of forward draft) , how can we read a forward draft and calculate a mean of mean draft .
    in this case can we use the hydrostatic tables of ship.
    if what can we do? and thank you again.

  3. Already corrected. Thanks.

  4. Hello dear teacher

    Thanks for learning, it’s just to correct the LCF calculation, the correct calculation would be
    1.60 = 78.46 – 74.00
    1.60 = 4.46 and not 2.46.

    May Allah bless you.
    Thank you very much

    Abu Valgy
    Marine Surveyor
    Mozambique

  5. Hi Budin.. You should refer to the explanation or notes available on sounding table itself. If no reference available, as common use, you could go with apparent trim to calculate.

  6. what trim do i use in sounding table, apparent trim or corrected trim?

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