Category: Draft Survey

Draft Surveyors Opinion

barge darft survey

Draft Survey Accuracy in Surveyor’s Opinion

Ship to ship operation between ship and barge is the most draft survey dispute cases experienced by draft surveyor. This condition is left question; How accurate is draft survey?

As known, there are many factors affecting the accuracy of draft survey. You can check at following post >>
– Draft survey the accuracy and factors effecting
– Improving accuracy of draft survey

By ignorance the accuracy of data provided by vessel and barge (hydrostatic table & tank sounding table), the disputes between ship’s and barge’s draft survey caused by :
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Negative Constant in Draft Survey

What is Ship Constant?

The ships constant is the difference between a vessels design lightship and it’s actual displacement when empty. The ships constant is determined by a draft survey. The ships constant will vary over the life of the vessel.

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Unintentional Reasons for Variations
– Sedimentation in ballast or fuel oil tanks
– Corrosion
– Fouling of hull
– Coating build-up (paintwork, tank coatings, etc.)
– Garbage collection, particularly in cargo holds
– Wear and tear of mechanical devices

Other Reasons for Variations
– Modifications to ship spaces
– Accumulation of stores (i.e., in paint locker, engineering stores, spares)
– Refit, overhauls, addition/removal of equipment.
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Inverse Draft Survey

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Few years ago, I have received the email from friend that asked regarding Inverse Draft Survey. The Inverse Draft Survey is doing when the ship has to split the cargo for two or more ports. The method is the same as common draft survey calculation, what the ship officer or surveyor needs to do is preventing cargo less or more discharge at the 1st port.

What is the purpose?
– To prevent cargo less or more discharge at one port.
– Surveyor can organize the work effectively.
– To prevent repetition of intermediate draft survey that cost a lot of time.
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Improving Accuracy of Draft Survey

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Previously has posted about the accuracy and factors effecting draft survey, check this link if you need. Now, the post below will relate to the way for improving accuracy of Draft Survey.

In draught survey operation several parties are involved and it is to advantage of each party to join the efforts to increase the accuracy. The parties involved are The buyers, the sellers, the charterers, the terminals and vessel’s staff.

Assuming that buyers, sellers and charterers are equally concerned about the correct weight of cargo, also the master (respectively chief officer to whom the responsibility of cargo weight is delegated) shortages and discrepancy may be a problem.
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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.
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Updated: Marine Survey Software

seven surveyorRecently, I have updated marine survey software for better performance and assist your fast calculation during surveying. In this version there are some updates includes:
– Clean and Larger interface with simple and easy data input for the survey.
– The software created basis Microsoft Excel files that works best with excel 2007-2013 and it could also working with excel 97-2003.
– The presentation is creates by Microsoft Power Point basis, it totally free to download. All version PP enable to open this.
– Smaller size file and performs faster file access.

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Draft Survey: Barge Overhang Method

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I found this alternative method from draft survey course book, hope it usable. Frankly, I never use this method yet, as we required the barge owners to provide the hydrostatic table for draft survey.

The overhang method use the same principles with the method of calculating the volume of a prism. The weight of the barge will be getting by multiplying the volume with the water density where the barge is afloat. Measure the dimension of the barge, before and after the loading/discharging is required for the length and width of the barge, barge freeboard, overhang aft and fore.

The method is applied when :
– The barge is of cut-up type.
– There is no table or data.
– The concerned parties agree on the use of overhang method for weight determination of barges.

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