Featured Video. By TMP Staff. January 11, Bulbous bows have been found to be most effective when used on vessels that meet the following conditions: The waterline length is longer than about 15 metres 49 ft. Here is a detailed video on this interesting subject: Facebook Comments. Subscribe to get latest updates. I've read and accept the Privacy Policy. Tags bulbous bow bulbous bow construction bulbous bow definition bulbous bow design bulbous bow in ship bulbous bow use function of bulbous bow what does bulbous bow do what is the bulbous bow for what is the function of bulbous bow.
TMP Staff. Related Articles. Comment: Please enter your comment! Follow us on Instagram themaritimepost. October 15, January 7, January 27, We use cookies to ensure that we give you the best experience on our website. In this way the vessel will run flatter and the overall wave height will be reduced. The vessel will pitch less which will cause less disturbance in the water and the passage of the vessel through the water will be achieved with less fuss and muss.
Any time a vessel can be moved through the water with less waves and overall disturbance to the surface less power has been transmitted to the water to create those waves. To be able to move a vessel through the water with no perceptible notice of its passage is the as yet unattained ultimate goal of all Naval Architects and the ultimate in power savings.
If you plan on doing some very long passages at a constant speed then you should have a bulbous bow. What is your next step? Contact a few brokers and boat dealers, ask about the efficiency of their vessel, ask about a bulbous bow. There are trawler yachts and then there are little ships designed to efficiently and economically take you anywhere you want to go on the face of the earth in safety and comfort.
Research and become knowledgeable about vessels in your market then spend your money wisely on a thoroughly designed vessel. Just add large amounts of ocean water and minimal amounts of power and many happy, inexpensive years of cruising lie before you. Bon voyage! I would like to start by saying that I find your webpage very useful and thorough. I am a naval architect, currently working at UBC as a teaching assistant while pursuing a masters degree.
However, I have read the section on bulbous bows, and find myself disagreeing with a few of your points on the operation of the bulbous bows. The second reason being that while there will be a contribution of the bulbous bow to the viscous damping and added mass of the motion of the vessel, the literature suggests that this is negligible.
Firstly, since the bow is immersed in the fluid, it should experience only a net positive buoyancy force from the hydrostatic aspect of the water. Since the bulbous bulb will displace fluid upwards and over it, there will be an acceleration of fluid for the water to get around the bulb.
This acceleration would presumably be most pronounced at the top, since there is no free stream condition here.
In a manner somewhat analogous to a shallow water flow, I would then expect the water to be flowing fastest on top of the bulb, and slower over the bottom of the bulb. This would mean if there were a dynamic force from the bulb, I would expect it to be an upwards force, although I would suspect it to be quite small.
Best regards,. Dan Vyselaar M. Candidate, University of British Columbia. I wish to commend you on your explanations of the attributes of the Bulbous Bow and its effects. I would also like to offer three points, that might be of additional help. When the added volume of a large Bulbous Bow, is used to reduce the volume of the forward part of the hull, while maintaining the same block-coefficient, a finer angle of entry can be achieved.
The resultant effect is that the wave-making resistance is reduced. This will result in a higher speed for the same power, or a power saving for the same speed. For a knot cargo ship, the increase is 0. For a Trans-Atlantic Liner it would have meant an increase of speed from Enough to win the Blue Riband in bygone times.
For a fast Container Ship Crossing the Pacific, it corresponds to a substantial saving in sailing time! When the shape of the Bulbous Bow is that of an upside down tear-drop, rather than cylindrical, the pounding effect is reduced and the tendency to keep the bow in the water to reduce squatting is enhanced. For a 15 knot ft. Its instantaneous velocity is zero, which in scientific terms, is known as a Stagnation Point.
So the pressure of the water particles at the bow is higher, thus giving rise to the crest of a wave. This wave is called the bow wave since it is generated due to the movement of the bow through the water, as shown in Figure 2. So with a straight bow, there is always a wave continuously formed, with its crest at the bow. Thus, it is evident, that we are wasting a part of the engine power in generating this wave.
What if this effect of wave-making can be reduced? If yes, then how? If we introduce another discontinuity any structure in the ship below the waterline which disturbs the laminar flow is regarded as a discontinuity below the waterline at the bow, in front of the stem of the ship, the discontinuity will itself give rise to another wave at its foremost point.
Since the stem is still at the waterline, it will generate normal bow waves. What if we can design the shape and position of the discontinuity in such a way so that the bow wave and the wave created by the discontinuity result in a destructive interference? Refer to Figure 3 Well, that is pretty much the principle behind the design of a bulbous bow. The destructive interference results in reduced wave-making of the ship, and which further reduces the wave-making drag of the hull form. Fig 3.
Bow wave and Wave generated by bulb, both out of phase. In the preliminary stages of the development of the bulb, the primary mission of the design was to reduce the wave-making drag.
Wave making is a significant characteristic of finer hull forms. That is why, you notice prominent Kelvin waveforms in cruise ships, liners, yachts, and naval cruisers. If you notice a bulk carrier or an oil tanker fuller hull forms , it is evident that these hull forms do not show prominent Kelvin wave patterns. Because the waterline width at the stem itself is so large or in other words, the discontinuity inflow is higher that the pressure rises to a level such that the bow wave height exceeds the threshold up to which a wave holds its properties.
In this case, the wave breaks right at the bow itself even before it travels along the ship length. So, are fuller hull forms more energy efficient in this respect?
Do fuller hull forms have high wave-making resistance? Do fuller hull forms have high wave breaking resistance? With this application, bulbs were also introduced in bulkers and tankers to reduce their wave breaking resistance. The different types of bulbs according to their shapes, positions and orientations are as shown below :. The position of the bulb significantly affects the phase difference between the bow wave and the bulb wave.
The volume of the bulb is a deciding factor of the amplitude of the resultant wave. Another advantage of the bulb is that it reduces the dynamic effects of the pitch motion of a ship.
In most ships, the interior of the bulb is used as a fore-peak ballast tank. In the case of high pitching, the forepeak tank is often ballasted to reduce the effect of pitching.
Well, the time period of pitching is directly proportional to the longitudinal distance of weights from the LCG of the ship. When the fore-peak is ballasted, it increases weight at a larger distance from the LCG of the ship which in most ideal cases is abaft the midship.
In other words, the pitch radius of gyration increases, therefore increasing the pitch period of the ship. Increased period of pitching results in less dynamic effects of pitch motion.
In the case of ice navigation, the bulb allows broken ice to glide along the hull with its wet side against the hull. The wet side of the ice having less friction coefficient reduces the overall drag on the ship. Bulbous bows have also been advantageous in housing bow thrusters, as can be seen in modern ships with bow thruster units. In naval ships that use high-frequency underwater acoustics like SONAR, bulbous bows act as protective housing, in addition to its positive effects of drag reduction.
After repeated model testing procedures of a wide range of hull forms and bulb shapes, it has been found that bulbs are not efficient at all service speeds relate it to Froude numbers.
In very low Froude numbers, bulbous bows have been found to increase the drag. Wonder why?
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