The bow of ships

We have the image that the sharp arch of ships, which forms an acute angle with the surface of the sea, is most suitable for navigation. Nowadays, however, most ships have a lamp of other shapes and sizes. It is a protrusion, normally immersed, that improves the hydrodynamic behavior of the ship. It was Re Froude who noticed in 1903 that the resistance to movement in a torpedo, which was installed a launcher tube in the lower part of the roda, when navigated with the covered tube compared to the ship without the tube. Shortly thereafter, DW Taylor projected the first arch ball in 1907 with the intention of increasing the speed of the battleship of the Tree. In the 1930s, various theoretical studies into the resistance to movement for golf formation in the arch of the ships were published. The theoretical results showed that the lamp generates a system of waves that is able to weaken them by overlapping with the bowl waves of the ship and therefore increasing the speed. The weakening is due to the fact that in this overlap the top of the waves produced in the sphere coincide with the valleys or breasts of the wave system of the bow of the ship. This overlap reduces the size of the wave and therefore also reduces the resistance to the movement of the ship. It is said that these waves are outdated. If the ball is not well designed, the bulb waves and arches can be in phase: match the ridges. In this case, they are added to overlaps and the resistance to movement is greater than that of the ship without bulb.

The first applications of the arch ball were made for high speed ships. So when the large oil tankers arrived, at low speeds, it seemed absurd to place the bow ball. Theoretical works, however, showed that while they were small while they were in full load, the effect of the ball was small in the ballast condition they achieved between 15% and 20% power savings. These works showed that the BOL effect described above is different for fast ships than in slow ships. This only reduces resistance in the ballast situation by breaking waves, which represent 20% of the total movement resistance. Initially the forms of the bulbs were very simple, but as experimental theoretical studies made, they started to use complex forms. It was also determined that the lamp can considerably improve the sail of the ship. In any case, it can be said that experiments are advanced faster than the theory. Nowadays the theory makes about the optimum volume of the bulb possible, as well as the most suitable position.

In the movement of the ship, in addition to the resistance to the movement produced by the waves, there is friction resistance due to the viscosity of the water. The influence of the lamp on viscous resistance is practically despicable.