Bulbous Bow
A Bulbous Bow is a rounded, bulb-shaped extension of the hull at the bow, below the waterline, fitted to most modern cargo ships. It works by creating its own bow wave that partly cancels the wave the hull would otherwise make, reducing wave-making resistance and so the power and fuel needed at the design speed.
The bulb is tuned to a particular speed and draught range, so its benefit falls away when a ship habitually operates far from its design condition — which is why some ships have been re-bulbed after slow-steaming became common, to re-optimise the bow for lower speeds.
At the right speed a bulbous bow can cut hull resistance by a meaningful margin, saving fuel and emissions over the life of the ship. Because the saving depends on speed and draught, matching the bulb to how the ship actually trades is now an active efficiency and decarbonisation lever.
Why do some ships have their bulbous bow modified?
A bulb is optimised for a design speed. When ships began slow-steaming to save fuel, some were fitted with a re-designed bulb suited to the lower speed, restoring the efficiency benefit.