Draft survey has the following three main advantages.
(1) Many countries of the world are connected by sea. Vessels can sail freely over the sea, so the same draft survey can be carried out anywhere in the world.
(2) A ship is like a large vessel, and a draft survey is conducted before and after a large amount of dry bulk cargo is loaded, and the difference between the displacements can be used to quickly calculate the weight of the loaded cargo.
(3) Draft surveys utilize the principle of Archimedes' buoyancy, a law of nature. This law is a principle of nature recognized by everyone in the world. Draft surveys conducted according to this principle can achieve high accuracy if the working environment such as weather and sea conditions is favorable.
On the other hand, the draft survey has the following two problems.
(1) Draft mark readings are affected by the working environment such as weather and sea conditions. A vessel is like a large container floating on the water, so it is directly affected by the wind waves and swell. The weather and sea conditions are constantly changing, and there are always waves of 10 cm to 30 cm. If the sea becomes rough due to the passage of a low pressure, etc., the water surface will fluctuate more than 50 cm, making accurate reading of the draft marks extremely difficult. In other words, the water surface condition at the loading and unloading ports is constantly changing, and the working environment for draft survey at that time changes accordingly, which causes differences in the readings of the draft marks. Furthermore, reading draft mark varies due to individual differences and parallax.
(2) Currently, there are two types of hydrometers in the world for measuring seawater density: one for relative density and one for apparent density.
The difference between the two types of hydrometers is whether or not air buoyancy correction is applied.
Please reffer to attached MARINE NOTICE for more information.
In order to improve the draft survey problems mentioned above, it is recommended to introduce the following two points.
(1) At the time of draft mark reading, a draft reading device (KENDRAFT) should be used
Usually, the following three fluctuations occur at the loading and unloading ports when reading draft marks.
‡@ Fluctuations due to wind waves and swell
‡A Fluctuations due to individual differences
‡B Fluctuations due to parallax
Draft readings in a work environment with the above fluctuations will inevitably result in differences in reading values. If you make it a scientific and rational on-site response, you can reduce the fluctuations in measured readings.
The use of KENDRAFT is highly effective in changing the current response with various fluctuations to a scientific and rational response.
Click here for more information.
(2) The same type of seawater hydrometer should be used at the loading and unloading ports
It would be best if seawater hydrometers were standardized worldwide, but due to the circumstances of each country, adjustments will take time. For the time being, it is necessary to establish a rule that the same type of hydrometer should be used at both loading and unloading ports.
By introducing the above two measures (a consistent survey from loading to unloading) into the current logistics, the on-site response will be scientifically standardized, and the quantity difference between the loading and unloading ports that has occurred so far will be greatly improved.
There are two methods to determine the quantity of a large amount of dry bulk cargo: draft survey and shore scale. Which method to use depends on the type of cargo and long-standing business practices. In the case of major dry bulk cargoes, iron ore and coal are subjected to draft survey, while grain is subjected to shore scale. Under such circumstances, it is said that there are many shortage losses for cargo that is settled on a shore scale. Generally, if the shortage of the discharged quantity exceeds 0.5% of the B/L quantity, the consignee will file a cargo claim against the carrier. There are several possible causes for a cargo claim, but the most common cause of dispute between the consignee and the carrier is the method of measuring the cargo weight.
Given the above, we believe that the largest difference in quantity is due to differences in shore scale itself. Cargo shortage loss is caused by the quantity difference between the loading and the unloading ports. As a prerequisite, in principle, the quantity of loading port and the quantity of unloading port must be measured and compared on the same scale. However, there are several types of shore scales in use at the site, such as hopper scales, belt scales and truck scales, and there are also differences in management between countries and owners. In other words, since they are measured and compared on different scales, it is natural that there will be a difference in quantity.
On the other hand, a vessel has the same scale and the same management anywhere in the world, and based on that scale, the same draft survey can be performed at loading and unloading ports. The only differences arise due to the waves at the time, individual differences, parallax and differences in specific gravity. At that time, by conducting a consistent survey from loading to unloading, if you can reduce the fluctuations in on site, you are able to significantly improve the quantity differences between the loading and unloading ports.
As mentioned above, there are some inconsistencies in the current method of determining quantities based on shore scale at the loading and unloading ports, and there are always some irrational aspects when comparing and verifying the loading and unloading quantities. In this situation, by introducing a consistent survey from loading to unloading by vessel and complementing the lacks of rationality in the current method of determining quantities, we believe that it is possible to create a system to prevent shortage claims.