Vessels operating at higher speeds, and those with high block coefficients, are often found to have a bulbous or protruding bow below the waterline.
It may be indicated that like most peculiarities of the immersed hull form this feature is usually intended to reduce the vessel’s resistance to motion under certain conditions.
The bulbous bow has several important advantages and does not present relevant disadvantages:
- Reduces the bow wave, due to the wave generated by the bulb itself, making the ship more efficient in terms of energy.
- Increases the ship’s waterline length, slightly increasing the ship speed, reducing the installed power requirements and so the fuel oil consumption.
- Works as a robust “bumper” in the event of a collision.
- Allows the installation of the bow thrusters at a foremost position, making it more efficient.
- Allows a larger reserve of flotation or a larger ballast capacity forward.
- Reduces the pitch movement.
Points to pounder for bulbous bow :
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.
- The vessel will operate most of the time at or near its maximum speed .
Bulbous Bows are fitted on ships because they can:
- give an increase in speed for similar input of Engine power. This may be up to 1/2kt when fully-loaded and up to C3/4 kt in ballast condition.
- give extra strength at bottom of Fore Peak tank.
- reduce vibration amplitudes in the Fore Peak tank.
However, Bulbous Bows are expensive to install. On small, slow service speed vessels they can actually cause increased resistance to forward motion.