Draft survey based on Archimedes' principle involves visually reading the draft mark, which is located on the waterline of a large vessel floating on the water, so the accuracy of the draft reading is greatly affected by the working environment, such as the weather and sea conditions at the time of work. In other words, the wind waves and swell on the water change depending on the time and place, there is individual differences in visual reading, and the draft mark reading value also differs due to parallax caused by the difference in height between the berth and the water surface. As a result, the accuracy of the draft readings vary and the range of fluctuation in draft survey quantity increases.
Currently, the reading method of the vessel's draft marks on site is carried out as follows.
There are a total of 6 draft marks (on the port and starboard sides of the bow, center and stern) on a vessel.
Usually, vessels are berthed at the wharf of shore side, so in that case, for the shore side, we read the three draft marks at the bow, stern and center from the berth.
On the other hand, for the opposite side of the shore side (hereafter referred to as the sea side), it is common to read only the center draft mark. And the readings of the bow and stern draft marks on the sea side are determined by calculating the left and right inclination values according to their respective widths, and adding or subtracting these values from the readings on the shore side.
And, when it comes to reading the center draft mark on the sea side, one of the following three methods is generally used:
(1) Method using a manometer
(2) Method using a Jacobs ladder
(3) Method using a draft boat
Either method will result in three fluctuations as mentioned above when reading the draft marks:@ Fluctuations due to wind waves and swell A Fluctuations due to individual differences B Fluctuations due to parallax. Unless these fluctuations are corrected, the accuracy of the draft mark reading values cannot be improved.
In other words, since there are various fluctuations in the actual working environment of draft surveys, we believe that it is necessary to improve the fluctuations by taking scientific and rational on-site measures.
The advantage of draft survey is that the weight of a large amount of cargo can be calculated in a short time by visually reading the draft marks of a vessel floating on the water, and if the working environment, such as the weather and sea conditions, is good, a high level of accuracy can be obtained.
However, the actual on-site conditions are constantly changing due to the influence of wind and waves, and waterline readings also fluctuate due to individual differences and parallax.
This draft reading device, KENDRAFT, was developed to reduce the above fluctuations. By using KENDRAFT, the reading of the center draft mark can be done scientifically and rationally, and then the accuracy of draft surveys could be improved.
Principle of KENDRAFT is very simple.
If water is taken into the pipe from a depth of about 5 meters below the water surface at the same atmospheric pressure, the water surface inside the pipe will stop at the same height as the water surface outside the pipe.
The water surface outside the pipe rises and falls due to wind and waves, but the water surface inside the pipe hardly moves because it takes in stationary water from a depth of about 5 meters.
Then, if you put a float in the pipe, the float will stop on the stationary water surface which is not affected by the wind and waves, and if you look at the draft mark where the float is stopped with a mirror, you can read the draft mark corresponding to the correct water surface.
Click here for more details of KENDRAFT.
Click here for more information about the benefits of introducing a consistent survey from loading to unloading.
In the field of maritime logistics, we carry out various marine survey services (condition surveys, P&I club surveys, loss prevention surveys, etc.) from a neutral and fair third-party standpoint.