Draft Survey in General

Draft survey is a calculation of cargo based on measurement of ship draft or laden before and after loading / discharge by taking weight calculate of goods in a ship. With comparing weight change of cargo may occur during operation loading / discharge, such as change in the water ballast, fuel, supplies etc.

Cargo weight, which measured with scale can be said accurately if scale routinely carried out calibration. On a calculation draft referring to Plimsoll mark. 

From definition mentioned above that clear the draft is the base of cargo counting, because cargo can be determined from depth of vessel into water, we can know weight ship cargo was (displacement) with the law Archimedes. In the daily activity of life, we measure/counting weight of goods with the scale. In the market would be a lot we find with various types of scales, for example, the balance toads, dacin, electronic (electronic scale) and there are still scales which are more accurate/soft namely digital scales for a measure of weight very small and light.


"So need to be known that draft survey is a largest scales tool in the world"

 KNOW SHIP DRAUGHT/DRAFT

Draught / draft is a series of numbers which placed in the right and left of a hull ( forward, mid, and after of the ship) this number is measured from the keel of a ship, it's used as measuring depthinstrument of ship sinking  in the water. 

There are 2 system draught mark of the ship:

1. Metric system

the standard numbers is : long 10cm, bold number 2 cm, the distance between of number  10cm, a unit of weight is a metric ton (MT).

2. Imperial system

the standard numbers is : long 6', bold number 1', the distance between of number 6', a unit of weight is a long ton.

After, Midships and Forward

Imperial system Metric system

The Factors That Affect in Accuracy Calculation of Draught Survey: 

• Weather factor 
• Crew ship cooperation   
• Age of the ship 
• Human error and a lack of skill 
• Non technical things

Implementation of Draught Survey

Phase I : Studied ship document which used in calculation of draft survey and seek information current ship condition.

Phase II : Reading  a ship in left and right of hull in the front ( forward ), the central (midships), behind (after)

Phase III : Measurements of fluid of ship ( fresh water, ballast water, fuel oil, diesel oil, lube . Oil, hydraulic oil, other).

Phase IV : measuring water density and ballast, fuel density based on information from last load report.

Phase V : Draught survey  calculation 

Books and documentation required in Draft survey calculation is Bibliography book, hydro static table, soundings table/tanks capacity curve

Ideal requirements for implementation draft survey:

• a ship not grounded / can be free floats 
• strap not too fast, the ships may free floating 
• a ship not sloping more than 2 degree 
• sign draft of a ship can be read clearly 
• soundings pipe/level gauge can be read clearly 
• the high waves no more than 0.5 m 
• trim of ship not exceeding the limit correction trim in table tank 
• the condition of table up to date
• a measuring instrument in good condition and calibrated
• no movement fluid and instrument loading while survey

In draft survey process call chief officer during draft survey operation, a ship do not:

- Loading or discharge transfer of water tank to tank ballast. - Loading or relocation fuel tank to tank - Insert or eject (swinging) valve. - and others.

The tools used in draught survey 

1. Draught reading device in rough sea : 

Equipment which used to see ship draft mark if there were a big wave, to do a survey while big wave required special tools that are: 

- a rope polypropylene 8 mm sufficiently

- white plastic hose  19 mm with long 6-8 m

- white plastic hose 12 mm with long 2 m

- iron weights

- plastic glue

- cork colored as float 

way using these devices: 

- place this device near markers laden 

- have earned that hose plastic  19 mm in the center from the water line 

- although the water in the condition wavy, a beacon  in hose of  this tool going to showing the surface of the water carefully 


2.Design water sampling device: 

an instrument for taken the example water 

equipment that are needed 

- polypropylene 

- tube stainless steel  14cm and long 60cm 

- iron weights 3.5 kg 

Avoid taken the example water for the measurement of density near channel  of the water cooling machine and hull ship


3 .Soundings tape specifications: 

- ribbon ( tape ) the length of min 25 m 

matter: stainless steel 

- 1mm thick 

- Divide of the distance per 10 mm 

- the weight of ballast 400gr 


4 .Hydrometer and tube reading 

Measuring instrument Density of water in a unit of kg per liters, furnished with a certificate laboratory tests which is recognized and regularly checked/calibrated of hydrometer with certified,o that known correction.


5 .Water finding paste 

paste that is used to obtain or knowing the reading of being conscientious from a higher liquid in a tank .Paste this is a material that can change colors become red when exposed to a liquid .Be used by means of applied to soundings tape to get the reading of being conscientious.


6 . - a calculator / laptop 

- flashlights 

- binocular; binoculars for recitation scale draught 

- a record book

- gloves

- clothing safety,  helmet,  shoes etc.

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