Have you noticed that how most of the ships have a strange protrusion at the forward end? It’s a big bulb-shaped lump of metal sticking out below the water and is called a ‘Bulbous Bow’.
The name origin is simple, as this metallic structure normally resembles the shape of a bulb, and is always placed at the bow of the ship. Hence it is called ‘bulbous bow’, and it serves a very specific purpose.
The size of the Bulbous bow is not always same, and varies as per the size of the ship on which they are fitted. Whether the ships are big or small, the bulbous bow are designed to serve one main function.
To understand what that function is, let’s first consider a ship without a bulbous bow. As this vessel, moves forward through the water, a pressure wave builds up at the front of the ship. This increases the height of the water, with the ship pushing it ahead, but that water has to go somewhere. What happens is that, the water flows back down the side of the hull, and will keep flowing back down, forming a wave all the way along the side of a hull.
Problem of having a constant wave on the side of the hull is that it increases the drag of the vessel. Thus, resulting in an inconsistent speed of the vessel, thereby increasing the fuel consumption of the vessel. To counter this very problem, bulbous bow comes in picture.
What Is The Bulbous Bow For?
A bulbous bow modifies the way the water flows around the hull, reducing drag and thus increasing speed, range, fuel efficiency, and stability. Ships with bulbous bows generally have twelve to fifteen percent better fuel efficiency than similar vessels without them.
Another function of the bulbous bow is that it increases the buoyancy of the forward part and hence reduces the pitching of the ship to a small degree.
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Vessels with high kinetic energy, which is proportional to mass and the square of the velocity, benefit from having a bulbous bow that is designed for their operating speed; this includes vessels with high mass (e.g. supertankers) or a high service speed (e.g. passenger ships, and cargo ships).
Vessels of lower mass (less than 4,000 dwt) and those that operate at slower speeds (less than 12 kts) have a reduced benefit from bulbous bows, because of the eddies that occur in those cases; examples include tugboats, powerboats, sailing vessels, and small yachts.
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).
- The bulb design is optimised for the vessel’s operating speed.
Here is a detailed video on this interesting subject:
Does the bulb also break the surface tension to allow the ship to push through the water easier?