Draft Survey: The Other Side

Distance Draft Mark From Perpendiculars

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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.

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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?

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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

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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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