SOLAS Reg 21, Passenger / Cargo Ships, Emergency Bilge Pump, Emergency Bilge Suction

Bilge Pumping Systems – SOLAS Regulations for Merchant Ships


For the safety of ships, there should be sufficient bilge pumping capacity available onboard the ships to pump out the accidental or otherwise, ingress of water in any compartment not designed for holding water or any other liquid. For this, there is Regulation 21 of SOLAS (Safety of Life at Sea) developed by IMO. There are different rules for Passenger Ships and Cargo Ships, those for Passenger Ships being most stringent. These regulations are devised to prevent accumulation of water in any compartment resulting in stability problems for the ship. Whether the water may contain oil or any pollutant is dealt with by different pollution prevention regulations.

Regulation 21 regarding …….

Number of Pumps for Bilge Pumping System

Minimum three power driven pumps for Passenger Ships and two for Cargo Ships are required, one of them may be driven by main propulsion engine in both the cases.

Sanitary, Ballast and General Service pumps may be accepted as power driven bilge pumps if connected with appropriate pipelines and valves.

One of the pumps shall be an Emergency Bilge Pump of submersible type having independent power source different from main power supply.

The bilge pumps and their power sources should be so located so that at least one pump is available in undamaged compartment.

Apart from the bilge main and direct suctions to different pumps, a Direct Emergency Suction connected to main circulating pump leading to the drainage level of the machinery space and fitted with non-return valve shall be provided in machinery space. The diameter of this Direct Emergency Suction should be at least 2/3rd the diameter of inlet pipe for steam ships and same as the diameter of inlet pipe for motor ships.


All the bilge suction valves should be of Non-return Type to prevent the accidental flooding of any compartment if, any bilge suction valve along with sea suction valve is left open by mistake.

Draining from enclosed cargo spaces on bulkhead decks of Passenger Ships and on freeboard deck of Cargo Ships

Sufficient drainage provisions should be provided either by scuppers leading to the shipside if deck edge immerses in water when the ship heels by 5° or more during rolling and, by drain pipes to lower hold which has bilge suction connection if the deck edge immerses in water when the ship heels by 5° or less, depending on freeboard to bulkhead deck or freeboard deck, in order to prevent flooding in these compartments.

Bilge Main Pipe Size

Speed of the water in the Bilge Main Pipe shall be at least 2 m/s when any of the power bilge pump operates. The diameter of the Bilge Main Pipe may be calculated by using a formula;

d = 25 + 1.68 x √L ( B + D )


d = Diameter of the pipe in mm

L = Length of the ship in m

B = Breadth of the ship in m

D = Moulded depth of the ship in m

Note: Source for the above information is SOLAS Regulations book by IMO.