Draft survey has the following three main advantages.
@ First, 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.
A Second, a vessel is such as a large container, 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.
B Third, draft surveys utilize the principle of Archimedes' buoyancy, a law of nature. This law was discovered by Archimedes in BC and is a principle of nature recognized by everyone in the world. Draft surveys conducted according to this principle can achieve extremely high accuracy if the work environment is good.
In general, the allowable difference for a draft survey is said to be Ton Per Centimeter (TPC) 1cm to 2cm. For example, the TPC for a Handymax type vessel (typically 52,000 - 58,000 t DWT in size) is about 50 tons, so the allowable difference is 50 tons to 100 tons.
On the other hand, the draft survey has the following two problems.
@ Draft mark readings are affected by the working environment such as weather and sea conditions. A vessel is like a large container floating on water, so it is directly affected by wind and waves. 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 work environment for draft survey at that time changes accordingly, which causes variations in the readings of the draft marks.
A There are currently two types of seawater hydrometers in use around the world. One is a hydrometer to measure relative density and the other is a hydrometer to measure apparent density. In general, the standard difference in measurements between these types is 0.002. In other words, when draft surveying a 50,000-ton cargo, the difference in hydrometer type alone will result in a difference of 100 tones.
In order to improve the draft survey problems mentioned above, it is recommended to introduce the following two points.
@ At the time of draft mark reading, a draft reading device (KENDRAFT) that is not
@ affected by the weather and sea conditions should be used
Draft survey is highly dependent on the working environment at the time. Imagine a situation in which you are reading the vessel's draft marks floating on the water under the various weather and sea conditions around the world. For example, let us say the correct draft mark reading is 6m83cm. If the sea is calm, you may be able to read 6m82cm or 6m84cm, but if the sea is rough, the difference can often be more than 2cm, such as 6m81cm or 6m85cm. However, with KENDRAFT, you can get the same 6m83cm reading in any weather and sea conditions as the following movie.
Under such circumstances, the following three differences can be considered at the loading and unloading ports when measuring and reading draft marks.First: Differences in personal error
Second: Differences in parallax caused by the quay condition where the vessel is berthed
Third: Differences in water surface conditions due to changes in weather and sea conditions
Draft readings in a work environment with the above differences will inevitably result in fluctuations in reading values. If you make it a standard and scientific on-site response, you can reduce the variation in measured readings.
The use of KENDRAFT is highly effective in changing the current response with varied differences to a standard and scientific response.
Click here for more information.
A 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 in order to improve the quantity difference.
Click here for more information.
By introducing the above two measures 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 claims for cargo that is settled on a shore scale. Due to the high unit price of such cargo, consignees often have shortage insurance. Generally, consignees file a claim for damages when the shortage ratio for the B/L quantity exceeds 0.5 % of the trade allowance. And the shortage loss minus the excess is covered by the shortage insurance.
As for the causes of shortage, there are various possible causes, such as insufficient loading quantity, loss due to sweating during sea transportation, discharge of bilge water during sea transportation, dust loss during loading and unloading handlings, quantity intake at the receiver of unloading port, residue on board due to contamination damage, but I believe that the difference in quantity due to the difference in shore scale is the largest. Shortage loss is caused by the quantity difference between the loading port and the unloading port. 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. Shore scales, however, include hopper scales, belt scales, truck scales, as well as differences in scale manufacturers and management methods by countries and owners, so the scale itself at loading port/unloading port is not the same even if it is called a shore scale. 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 ship has the same scale anywhere in the world, and based on that scale, the same draft survey can be performed at loading port/unloading port. However, in doing so, it is essential to introduce the above-mentioned concrete measures to improve the draft survey problems.
To improve this shortage loss, it is highly effective to conduct a consistent survey from loading to unloading by a draft survey, which will be introduced as a new measure.
Vessels have the same scale anywhere in the world, and we surveyors use the same scale to conduct draft surveys. At that time, by introducing KENDRAFT and the same type of seawater hydrometer at loading and unloading ports, it is possible to reduce the variation in on-site response caused by differences in personal error, parallax, water surface conditions and hydrometer types, and to make it a scientific and standard on-site response.
In other words, when we introduce the consistent survey from loading to unloading into the current logistics, we can greatly improve the shortage rate for B/L quantity.