erickp21 ® 17-Sep-2023 03:47
Hello everyone, I am a Draft Survey Student, I normally do Tally Surveys, cargo certification and inspection but lately want to learn more about Draught Surveying.
How do you go about calculating drafts that you cannot see.
I have 2 scenarios:
Number 1: Vessel moored. I can see all of the starboard draft marks but none on the port side.
Number 2: Vessel moored. I can see all of the Starboard draft marks and the ship has a tube on midship that goes from side to side with markings on each side. I can just take that measurement and add or substract to the draft i can see?
Any guides, formulas or books that you can recommend will be duly appreciated. Thank you
mariners728013 18-Sep-2023 19:46
erickp21, You can refer to this book

Draught Surveys a Guide To Good Practice, 2nd Edition - JIM DIBBLE, PETER MITCHELL and North of England P&I Association [2009, PDF]

Author: JIM DIBBLE, PETER MITCHELL and North of England P&I Association | Year: 2009 | Language: english | Format: PDF | Quality: eBook | Pages count: 54 | Genre: Guide

Open released by virtual

Regarding the the 2 scenarios, that you have pointed out, In scenario 1 - Using the U tube or as we call it manometer, you can read the visible midship draft and apply the difference in the manometer / U tube proportionally to the visible draft. Eg- if the beam of the vessel is 25metres, then u can have a long transparent tube running from from 1 side to another and kept standing at the shipside railings or u can have a U tubes separated by say 2.5 metres only. so in the case of the tube running the entire beam, the difference in the liquid level between both sides will be same as the difference between the drafts on both sides. While if u use a U tube with a difference of 2.5 metres placed absolutely on the center line, then the difference in water level of the tube will have to be multiplied by 10 and applied to the visible draft. Now regarding the ford and aft drafts, there are ships plans where it gives the horizontal distance from the keel upwards between the port and starboard marks for forward and aft. This can be used as proportional to the beam and distance of the midship drafts and correction applied.
Hope this simplifies the matter. This will help in both the scenarios.
erickp21 ® 20-Sep-2023 17:34
mariners728013, Thank you so much for the response.
Then yeah, with that manometer running across the beam is as simple as adding or subtracting to the non visible draft.
I asked yesterday a draft surveyor and he explained that using a formula you can calculate the difference in midship draft using a clinometer. I don't know if you have experience with that but I forgot to ask him if the result of that calculation can be applied to fwd and aft as well.
mariners728013 21-Sep-2023 14:03
erickp21, By using the inclinometer you can find out the drafts on the other side by simple trigonometry formulae. But that will be only for the midship draft. The forward and aft drafts it will not be possible to do so simple because the lateral distance between the port and starboard marks are not uniform from the keel upwards. while for the midship, the distance between the port and starboard marks is uniform for the entire length from bottom to up.
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