More about waterline
The topic of discussion is what is called "on the surface." Seriously, it is directly drawn on the surface of the ship’s sides. Many may think that we are talking about the name of the swimming means, but no, on board you can meet not only him. It is also there - the saving strip, transformed over time and the needs of seafarers, into a variety of display options.
So, waterline! You all know this word very well and assume what it means. And I am sure that you are not mistaken, because everyone from school knows that, thanks to the waterline, you can “by eye” load the ship with grain, fuel and lubricants enriched with uranium, melt water, Chinese sneakers, broken bricks or ostrich feathers.
We also know that two opposing forces act simultaneously on any ship: attraction and Archimedes. They work in opposite directions: the force of attraction is vertically down to the center of the planet, and the second is vertically up. If everything is approximately clear from the first, then I will remind the second that a buoyant force acts on a body immersed in water, equivalent to the weight of water in the submerged body volume.
Consequently, designing ships so that these two forces compensate each other - it is possible to predetermine in advance how the ship will be submerged in water with or without cargo. For the depth to which the ship is immersed in water, a special term was invented - draft. And, as you understand, for each watercraft there is its maximum allowable value of draft, which is marked by the waterline.
In fact, a waterline is two in one: a mark on the vessel’s hull, on which it is (or may be) in the water and a mark of the balance of two opposing forces.
Everyone, young and old, knows that water above the mark is bad. And those seafarers who once built ships without regard to the discussed "security line" often decorated the bottom of the world ocean with swimming facilities, due to a banal overload and violation of the ship’s stability.
Today, when science has strongly fled forward, for each ship, depending on its shape and purpose, the correct waterlines are calculated. There are always several of them and they are determined in advance — calculated, constructive, operational, cargo, theoretical — it is easy to guess their assignments from the names.
In addition, the area of the waterline is used to calculate the so-called hull completeness coefficient - numerical indicators characterizing the completeness of the ship's lines. The greater the coefficients of completeness, the fuller the contours of the vessel and, conversely, the smaller it is, the more contours and sharpened the contours. Fuller contours mean greater tonnage, but a lower travel speed compared with vessels with lower values of the coefficient of completeness.
Since the size of the plane-outlined line and its shape have a significant impact on the speed and stability of the vessel, it can safely be safely assumed that the line under discussion has a rather serious influence on the appearance of the future ship at the design stage.
That's how difficult it is - waterline!