Reeds Vol. 5: Ship Construction for Marine Engineers by Paul A Russell & E A Stokoe

Author:Paul A Russell & E A Stokoe
Language: eng
Format: epub, pdf
Publisher: Bloomsbury
Published: 2022-08-15T00:00:00+00:00

Figure 7.5 Solid floor in pounding area

Bulbous Bow

One of the most important tasks facing designers of ships is to optimise hull performance. There are two aspects to this activity: the first is to reduce hull resistance and the second is to reduce the effect of ‘wave drag’.

The act of pushing the vessel through the water will create a bow wave. If a sphere is immersed just below the surface of the water and at the bow of the ship the wave from the sphere interferes with the normal bow wave created by the vessel and results in a smaller bow wave. Thus the force required to produce the bow wave is reduced.

At the same time, however, the wetted surface area of the ship is increased, causing a slight increase in the frictional resistance. In slow ships the effect of a bulbous bow could be an increase in the total resistance, but in faster ships, where the wave making resistance forms a large proportion of the total resistance, the latter is reduced by fitting a bulbous bow. A bulbous bow also increases the buoyancy forward and hence reduces the pitching of the ship to some small degree. Optimising the design of the bulbous bow is very important. On modern ships the operating range might also be increased and therefore the design of the bow might not be as straight forward as first thought by the designers.

Although the actual design of a bulbous bow will be optimised to an actual vessel, a typical construction of the bulbous bow is shown in Figure 7.6. The stem plating is formed by steel plates supported by a centreline web and horizontal diaphragm plates 1 m apart. The outer bulb plating is thicker than the normal shell plating, partly because of high water pressures and partly due to the possible damage by anchors and cables.

It is often found that due to the reduced width at the waterline caused by the bulb, horizontal stringers in the fore peak prove uneconomical and complete perforated flats are fitted. The framing of the bulb could be joined to the general frame of the fore peak using diaphragm plates.

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