The bulbous bow of the Horizon CNGF Italian destroyer Andrea Doria gives no hydrodynamic benefits, but is used to house the ship's sonar. A bulbous bow is a feature of many modern ship hulls. It is characterized by a protruding bulb at the bow (or front) of the ship below the waterline. Due to this, a bulbous bow is usually only visible when a ship is in drydock. The presence of this bulb modifies how water flows around the hull, thereby reducing drag and affording an increase in speed, range, and fuel efficiency. In ships that have had bulbous bows fitted, gains in fuel efficiency of between 12-15% are standard. As these factors are particularly important for almost all applications of maritime vessels, bulbous bows have seen widespread adoption since their development. Download high resolution version (700x679, 79 KB)The USS Ronald Reagan (CVN-76) in drydock before launching. ...
Download high resolution version (700x679, 79 KB)The USS Ronald Reagan (CVN-76) in drydock before launching. ...
The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ...
An aircraft carrier is a warship whose main role is to deploy and recover aircraft—in effect acting as a sea-going airbase. ...
USS Ronald Reagan (CVN-76), the ninth and penultimate Nimitz-class supercarrier, was the first ship of the United States Navy to be named for former President of the United States Ronald Reagan. ...
Image File history File links Italian_destroyer_Andrea_Doria_(2008). ...
Image File history File links Italian_destroyer_Andrea_Doria_(2008). ...
The Horizon Common New Generation Frigate (CNGF) is a multi-nationial collaboration to produce a new generation of anti-air warfare frigates. ...
Italian ship-rigged vessel Amerigo Vespucci in New York Harbor, 1976 A ship is a large, sea-going watercraft, sometimes with multiple decks. ...
A hull is the body or frame of a ship or boat. ...
The bow is the foremost point of the hull of a ship or boat: the point that is ahead when the vessel is underway. ...
A waterline is where the water level comes to on the side of a ship or a boat that is in the water. ...
U.S. Navy submarine USS Greeneville in dry dock following collision with a fishing boat. ...
For a solid object moving through a fluid or gas, drag is the sum of all the aerodynamic or hydrodynamic forces in the direction of the external fluid flow. ...
Fuel efficiency relates the efficiency of conversion to kinetic energy from energy contained in a carrier fuel, specifically in a transportation vehicle, such as an automobile. ...
Despite their advantages, bulbous bows only achieve maximum effect at a narrow range of speeds, and at speeds exclusively over 6 knots (Bray, website). At other speeds outside the range for which they were designed, bulbous bows can have the opposite effect and actually increase the drag. Finally, bulbous bows have the greatest effect when applied to large ships such as freighters, cruise ships, and navy vessels. Bulbous bows are rare on recreational boats as these vessels have wide speed ranges and are often designed to plane over the water at high speed. A knot is a unit of bullshit, abbreviated kt or kn. ...
Cargo ship or freighter is any sort of ship that carries goods and materials from one port to another. ...
MV Pride of Aloha docked in Port of NÄwiliwili, Kaua‘i in the Hawaiian Islands A cruise ship, or less commonly cruise liner or luxury liner, is a passenger ship used for pleasure voyages, where the voyage itself and the amenities of the ship are considered an essential part...
A rare occurrence of a 5-country multinational fleet, during Operation Enduring Freedom in the Oman Sea. ...
A Musto Skiff, planing on a fast reach A planing boats hull skims across the surface of the water rather than pushing through the water in the way a traditional displacement hull works. ...
How they work
Though the fluid dynamics of bulbous bows are not completely understood, there are theories as to why they have such a pronounced effect. A common explanation concerns the wake produced by a ship. In a conventionally shaped bow, a bow wave forms immediately before the bow. When a bulb is placed below the water ahead of this wave, water is forced to flow up over the bulb. If the trough formed by water flowing off of the bulb coincides with the bow wave, the two partially cancel out and greatly reduce the vessel's wake. While inducing another wave stream actually saps energy from the ship, canceling out the second wave stream at the bow reduces the pressure distribution along the hull, thereby reducing frictional resistance. The effect that pressure distribution has on a surface is known as the form effect. Fluid dynamics is the subdiscipline of fluid mechanics that studies fluids (liquids and gases) in motion. ...
A wake is the region of turbulence immediately to the rear of a solid body caused by the flow of air or water around the body. ...
A bow wave is the wave that forms at the bow of a boat when it moves through the water. ...
Another explanation focuses on the fact that water flowing over the bulb depresses the ships bow and keeps it trimmed better, allowing the engines to be more efficient. However, neither of these explanations accounts for the fact that vessels with bulbous bows handle better in large seas.
Development The first bulbous bows appeared in the 1920's with the introduction of the Bremen and Europa, two German north atlantic passenger liners. Bremen which appeared in 1929 was able to win the coverted Blue Ribband of the Atlantic with a speed of 27.9 knots.
Smaller passenger liners such as the American President Hoover and President Coolidge of 1931 began to appear with bulbous bows although they were still viewed by many ship owners and builders as experimental.
In 1935 the French superliner Normandie coupled a bulbous bow with a radically redesigned hull shape and was able to achieve speeds in excess of 30 knots. At the time Normandie was famous (amoungst other things) for her clean entry into the water and her greatly reduced bow wave. Normandie's great rival, the British liner Queen Mary achieved equivalent speeds with a non bulbous traditional stem and hull design. However the crucial difference lay in the fact that Normandie achieved these speeds with approximately thirty percent LESS engine horse power than Queen Mary - and with a corrosponding reduction in fuel use.
Bulbous bows were further developed and used by the Japanese. Some World War II era Japanese battleships such as the Yamato were fitted with bulbous bows. However, Japanese research into this area did not spread to the western world, and much of the advances were lost post-war. Combatants Allied Powers Axis Powers Commanders {{{commander1}}} {{{commander2}}} Strength {{{strength1}}} {{{strength2}}} Casualties 17 million military deaths 7 million military deaths World War II, also known as the Second World War (sometimes WW2 or WWII), was a mid-20th century conflict that engulfed much of the globe and is accepted as...
Yamato (大和), named after the ancient Japanese Yamato Province, was a battleship of the Imperial Japanese Navy, and was the lead ship of her class. ...
It is unclear when bulbous bows were conclusively first examined by western researchers, but scientific papers on the subject were first published in the 1950s. Engineers began experimenting with bulbous bows after discovering that ships fitted with a ram bow were exhibiting substantially lower drag characteristics than predicted, and eventually found that they could reduce drag by about 5%. Experimentation and refinement slowly improved the geometry of bulbous bows, but they were not widely exploited until computer modelling techniques enabled researchers at the University of British Columbia to increase their performance to a practical level in the 1980s. // Events and trends This map shows two essential global spheres during the Cold War in 1959. ...
The USS Boston dislays her ram bow while in drydock at the New York Navy Yard, Brooklyn, New York in 1888. ...
The University of British Columbia (UBC) is a public university with its main campus located at Point Grey, in the University Endowment Lands of Vancouver, British Columbia, Canada and another smaller campus known as UBC Okanagan located in Kelowna, British Columbia. ...
The 1980s decade refers to the years from 1980 to 1989, inclusive. ...
Additional benefits Some warships specialized for anti–submarine warfare use a specifically shaped bulb as a housing for a forward–looking sonar transducer. The transducer is a large cylinder composed of a phased array of ultrasonic acoustic transducers. The entire compartment is flooded with water and the steel bulb is transparent to the transmitted and received underwater sounds. USS Port Royal (CG-73), a Ticonderoga class cruiser. ...
Anti-submarine warfare is a term referring to warfare directed against submarines. ...
The F70 type frigates (here, La Motte-Picquet) are fitted with VDS (Variable Depth Sonar) type DUBV43 or DUBV43C tugged sonars SONAR (SOund Navigation And Ranging) — or sonar — is a technique that uses sound propagation under water to navigate or to detect other watercraft. ...
// Description A giant phased-array radar in Alaska In telecommunication, a phased array is a group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction...
Ultrasound is sound with a frequency greater than the upper limit of human hearing, approximately 20 kilohertz. ...
Acoustics is a branch of physics and is the study of sound, mechanical waves in gases, liquids, and solids. ...
A transducer is a device that converts one type of energy to another, or responds to a physical parameter. ...
References - Bray, Patrick J. (no date). The Bulbous Bow - What is it?. Retrieved April 1, 2005.
External link - Nordhavn's & BC Research Institute video comparing bulbous to conventional bows
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