Construction and purpose of a bulbous bow.

Construction: The bulbous bow is a roughly pear-shaped or blunter solid forepeak projection from the stem, below the load waterline, formed by specially shaped shell plating. The bulb is built by a thick, heavily plated shell with internal framing made up of transverse webs (swash bulkheads/forepeak frames) and fore-and-aft stringers that connect it to the stem of the vessel and the side plating. It extends well below the waterline and often contains a forepeak collision-bulkhead behind it. The stanchion, stem bar and the bulb take the pounding and panting loads; the bulb shell plates are thicker at the leading edge and stiffened by the framing arrangement. The bulb usually joins the ship's side with a smooth radius, and the whole forepeak is subdivided and stiffened.

Why fitted: when a ship moves, water is pushed aside creating a bow wave. At moderate speeds (Froude number about 0.25 to 0.35 typical of merchant ships) the bulb creates its own system of waves, and by correct sizing and position the bulb's wave trough cancels part of the bow wave crest of the hull, reducing the wave-making (residual) resistance. The net result is a reduction in total resistance at the design speed, giving:

• lower installed power and fuel consumption (better EEDI);
• improved ship propulsion economics;
• reduced bow wave and stern wave of the ship in general;
• assistance in carrying forefoot buoyancy, helping the ship's longitudinal distribution of buoyancy and allowing finer, faster forms without a large bow wave penalty.

The bulb is essentially an interference device that cancels bow-wave energy, and is most beneficial at the design/ballast speeds of displacement vessels (bulk carriers, tankers, container ships, general cargo, ro-ro).