Bow (shipbuilding)
The bow is the mostly aerodynamically shaped front part of the hull of a ship or boat. (The rear part of a ship is called the stern .) The front end of the bow is formed by the fore stem , in wooden ships usually a square wooden beam. A part of the ship that protrudes over the bow is called a galion .
In the course of time, different designs have emerged in which optical, fluidic and / or other aspects have influenced the shape.
Boat bow
The usual boat bow is rounded. This design is self-evident in the planking of the ribs when the planks for Steven bent. The voluminous shape creates a lot of buoyancy and is therefore usually chosen for small boats ( folk boats , rowing boats).
Battering bow
In the ancient warships often had a Rammbug (also Rammsporn called), the far-sticking forward. This could seriously damage enemy ships below the waterline. It is believed that the ram bow was a kind of ancient forerunner of the bulbous bow; Dolphins swimming on the surface of the water served as a model.
When armor had an advantage over artillery with the advent of ironclad ships , the ramming bow was reintroduced. The naval battle of Lissa (1866), which was decided by a ramming, initially confirmed this development. However, as the artillery advance (see explosive shell ) around 1900 led to the defeating of the enemy at a great distance, the battering bow lost its importance. Nevertheless, they held on to it, even though their own ships were sunk again and again during turning maneuvers through unintentional ramming.
Even the warships of the First World War still had - at least in terms of shape - a battering bow. This was usually not suitable for ramming enemy ships; it was of practical importance only when ramming submarines . It should be noted that the ships were built with a less pronounced bow during the war and shortly before it. For example, the yacht of Emperor Hohenzollern or the small cruisers of the Gazelle class , which were all built around the turn of the century, had an extremely pronounced bow. Towards the end of the war the ships planned or already launched had a straight bow stem.
As a side effect of the ram bow development, deviations in the actual draft and the actual speed of new ships with a ram bow compared to the calculated design values were measured again and again . These deviations were caused by buoyancy and flow effects, which occurred because some ramming bow shapes were more or less random in shape to approximate a bulbous bow. This was the basis for later series of tests and ultimately led to the bulbous bow.
Clipper bow
The stem of the clipper bow has a double curved shape. At about the level of the waterline, it is relatively steep, while it becomes shallower above and below, which results in a smooth transition of the stem to both the keel and the bowsprit . It has a concave shape so that the ship plunges more calmly into the waves in rough seas and “ pounds ” as little as possible .
Similar to this bow shape is the "Atlantic bow" of large German warships from the late 1930s.
Vertical or steamer bow
The steamer stem is straight vertically or if necessary with a slight fall ahead. The shape developed with the advent of steamships as a simplification of the previously used bow shapes with bowsprit . In the period after the First World War, the steamer stem was replaced by more recent developments such as the normal bow and Maier stem and was only used where the length was limited, for example by lock dimensions (inland vessels, Great Lakes vessels). More recently, the hull shape has experienced a renaissance due to its advantages in larger ships and more varied drafts and speeds.
Maierform bug
This hull shape, introduced by the Maierform company , with its characteristic V-shaped frames and unusual rounded stem, has been built since the late 1920s.
Normal bow
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The foredeck with a straight (on passenger ships also slightly convex) bow projecting forward is the normal shape. Dropping stem shapes offer greater reserve displacement and reduced spray build-up in rough seas, as well as increased protection in the event of collisions.
Bulbous bow
The bulbous bow - also known as the bulbous bow - is the distinctive teardrop-shaped stem on the underwater bow of many large modern ships. It is also known as the Taylor bead, named after David Watson Taylor , chief engineer in the United States Navy during World War I. The first large ships to be equipped with it were the Mackensen-class large cruisers under construction for the Imperial Navy . However, they were not completed by the end of the First World War and had to be scrapped. This means that the two express steamers Bremen (1929) and Europa (1928) are considered the first larger ships to be equipped with a bulbous bow.
Advantages of the bulbous bow include:
- A bulbous bow tailored to the trim position , speed and hull shape of a ship can have a positive effect on the wave pattern of a moving ship. It almost avoids the bow wave that otherwise occurs , which causes most of the water resistance.
A ship traveling as a displacer can normally not exceed its hull speed , which depends on the length of the waterline . When the hull speed is reached, it drives against the self-generated bow wave, while the stern wave rises behind the hull, the stern sinks into the stern wave trough and the ship therefore has to travel upwards in its own wave system. Even higher propulsion power does not allow the ship to travel faster, but only increases the bow and stern waves.
In order to be able to increase the speed, the wave system of the ship has to be changed or destroyed by destructive interference . This is what the bulbous bow achieves: it creates a second wave system that can reduce the size of the bow and stern waves until they are extinguished. In this way, the ship reaches a higher speed with 10–15% less fuel consumption. Other positive effects such as a better flow to the propeller also arise, but are considered to be of secondary importance. - If the bulbous bow is in front of the forward perpendicular , the water it displaces is drawn under the ship at a higher speed than the surrounding water by vortex effects , which further reduces the hull's resistance.
The main disadvantage of the bulbous bow is the high manufacturing costs due to the complex shape, which has to be manufactured with relatively small tolerances. In addition, the bulbous bow only achieves its effect in a narrow speed range for which it has been specially designed and in a position just below the water surface. Outside these tight conditions, the water resistance of the vehicle can even be increased.
The bulbous bow is therefore unsuitable for ships that travel at a constantly changing speed (e.g. tugs with and without a load, sailors with a lot or little wind) or vehicles that travel with constantly changing trim positions (e.g. sailing vehicles, who rarely ride upright).
The bulbous bow worsens the maneuvering properties, but this is not significant and is far outweighed by the advantages. Because of their enormous length and the need for maneuvering, e.g. B. in locks, many ships have a bow thruster anyway . In view of expensive fuel ( heavy oil ), it can even be worthwhile to optimize an existing bulbous bow ( retrofit ). Since the beginning of the shipping crisis in summer 2008, many ocean-going vessels have been traveling at reduced speed (“ slow steaming ”) in order to save fuel. Their bow is often designed for a high speed (over 20 knots); an optimal bulbous bow for lower speed has a different shape. The Maersk shipping company, for example, has ten container ships converted. The new noses are said to save 1–2% fuel. The nose shape is the subject of research in fluid dynamics and ship theory.
Icebreaker bow
The bow of an icebreaker is convex and relatively flat in the area of the waterline, so that the ship can hit the ice with momentum, so that it breaks apart under the weight. With the Thyssen Waas bow , however, almost right-angled bow constructions are also used in icebreakers.
X-Bow
The Ulstein X-Bow is a bow shape without a bulbous bow, the stem of which tilts backwards above the waterline. The advantages of the shape are the lower flow resistance and higher speeds in difficult sea conditions. Due to the more complete stern in the area just above the water surface , ships with X-Bow achieve higher lift with less immersion, which leads to softer swell movements of the ship's hull and lower negative accelerations.
literature
- With a modified bow shape on course for economy · The bulge is increasingly being replaced by a straight stem, thus reducing fuel consumption with every draft . In: Daily port report of March 13, 2015, special supplement Schiffbau & Reparatur, p. 8, DVV Media Group, Hamburg 2015, ISSN 2190-8753
Web links
Individual evidence
- ↑ a b H. Schneekluth: Designing ships . Lectures, TH Aachen. Koehler, Herford 1984, ISBN 3-7822-0351-8
- ^ Ernst Foerster : Johow-Foerster: Aid book for shipbuilding , first volume, Julius Springer, Berlin, 1928, p. 39.
- ^ Ernst Müller: Eisenschiffbau , BG Teubner Verlag , Leipzig, 1910, p. 30ff.
- ^ A b Karl Heinz Rupp: Drawing of Ship Lines , Institute for Ship Design and Ship Theory of the University of Hanover, October 1981, p. 33.
- ↑ Frank Behling, Thomas Luczak: Fore ships in transition: Will the bulbous bow die out? , In: Ostsee-Zeitung , April 20, 2015.
- ^ Karl Heinz Rupp: Drawing of Ship Lines , Institute for Ship Design and Ship Theory of the University of Hanover, October 1981, p. 34.
- ↑ Boats exclusive 3/2006: Bulge bow on yachts ( Memento of the original from April 2, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 1.8 MB)
- ↑ The nose job: Why 10 of our ships are getting a new bulbous bow (December 21, 2012) ( Memento of the original from July 25, 2013 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Container Ship Nose Jobs - Maersk Retrofits Bulbous Bows for Slow Steaming - See more at: http://www.oldsaltblog.com/2013/03/container-ship-nose-jobs-maersk-retrofits-bulbous-bows-for- slow-steaming / # sthash.WDXZDoXE.dpuf
