Section 10 High pressure sea-water systems

10.1.1 The requirements in this Section are additional to those contained in Vol 2, Pt 7, Ch 5, 2 Construction and installation of this Chapter.

10.1.2 High pressure sea-water (HPSW) systems are to continuously supply and distribute sea-water at a pressure of generally not less than 7 bar throughout the ship to provide water for fire-fighting, magazine spraying, pre-wetting, bilge and dewatering eductors and emergency cooling. See Vol 2, Pt 7, Ch 5, 10.2 Pump units 10.2.6 for water pressure requirements.

10.1.3 The pumping and delivery capacities and pressures from the HPSW are to be sufficient to support damage control and fire-fighting policy, procedures and techniques, including pre-wet requirements that are to be declared in the System Design Description required by Vol 2, Pt 7, Ch 5, 1.3 Documentation required for design review 1.3.2.

10.1.4 Ship-side valves and fittings are to comply with the requirements of Vol 2, Pt 7, Ch 2, 2.5 Ship-side valves and fittings (other than those on scuppers and sanitary discharges) as applicable.

10.2.1 Three or more HPSW pumps are to be provided of sufficient capacity to supply the total pumping capacity defined in Vol 2, Pt 7, Ch 5, 10.2 Pump units 10.2.3 with any one pump out of action. At least one of the pumps is to be capable of supplying HPSW in a dead ship condition.

10.2.2 The pumps are to be located in separate compartments and zones such that the loss of one compartment or zone or failure in equipment will not render the other pumps inoperative.

10.2.3 The total pumping capacity of the HPSW pumps with one pump out of action shall provide for the greatest of the following:

1. The amount required for pre-wetting.

2. The amount required for a fire in the largest space protected by a fixed spray system plus 40 m³/hr boundary cooling from hoses.

3. The amount required for a major fire outside the spaces protected by fixed spray systems, using 100 m³/hr boundary cooling for each fire. The minimum number of fires to be considered is as follows:

   1. Displacement at deep draught of under 4,000 tonnes – one fire

   2. Between 4,000 and 10,000 tonnes – two fires

   3. Between 10,000 and 20,000 tonnes – three fires

   4. Over 20,000 tonnes – four fires

   Reference is also to be made to the System Design Description required by Vol 2, Pt 7, Ch 5, 1.3 Documentation required for design review 1.3.2 where the number of fires to be considered may also reference amongst other items, the type of ship, number of personnel on board and number of fire zones.

4. The largest single magazine or ammunition transfer space spray requirement plus 40 m³/hr boundary cooling.

5. The hangar spray requirement in the largest area contained by a fire curtain.

6. A flight deck fire requiring one third of the total foam branch pipes fitted in multi-aircraft landing (multi-spot) ships or two foam branch pipes in single aircraft landing (single spot) ships.

7. The amount required for any specific fire-fighting scenarios defined by the System Design Description.

If the factor determining the total pumping capacity is (b), then any pumps located in the space are to be added to the overall number of pumps required.

10.2.4 The capacity of each pump is to be not less than that required to supply water for the eductor capacities referred to in Vol 2, Pt 7, Ch 2, 6.3 Capacity of pumps and educators.

10.2.5  The sea suctions to HPSW pumps are to be provided with an air elimination arrangement to ensure that the running and standby pumps do not become air-locked.

10.2.6 HPSW pumps are to be arranged to operate continuously with automatic and switched means of starting of standby pumps on sea-water demand. Automatic starting of standby pumps may be achieved by sensing when the system pressure falls below a pre-set level. The continuous and minimum supply pressures in the HPSW distribution system are to be in accordance with the System Design Description required by Vol 2, Pt 7, Ch 5, 1.3 Documentation required for design review 1.3.2.

10.2.7 HPSW pumps are to be provided with high temperature alarms for components that may become overheated when the pump is running in low or no flow demand conditions.

10.2.8 Where HPSW pumps can develop a pressure greater than the design pressure of the system, they are to be provided with pressure relief/control devices on the pump discharge to effectively limit the pump discharge pressure to the design pressure of the system.

10.2.9 Strainers capable of being cleaned without interruption of water flow to the pumps are to be provided in the suction pipes.

10.3.1 The arrangement of the HPSW system is to ensure continuous availability of supply in the event of the loss of any compartment or zone. Isolating valves are to be fitted in each branch from the main distribution system to permit isolation of any damaged branches.

10.3.2 HPSW should be supplied throughout the ship by means of a ring main system. In multi-spot ships fitted with a between deck hangar, a second ring main should be provided. These ring mains are to be cross-connected but may share the same pumps. Alternative arrangements to a ring main system will be considered where a vulnerability assessment has demonstrated that continuous availability of HPSW can be ensured whilst satisfying the system arrangement requirements of this Chapter.

10.3.3 Ring mains are to extend over the middle two thirds of the length of the ship, one half to port and the other to the starboard side. Each ring main is to be cross-connected across the ship in separate fire zones recognising any vulnerability requirements stated by the Owner. The main is to be extended forward and aft of the ring main by a single line of piping at the centre.

10.3.4 The HPSW system is to be capable of being isolated into separate sections by local and remote controlled valves at the fire zone boundaries. In addition, isolating valves are to be fitted at the following locations:

1. At the riser from the pump to the ring main.

2. In the ring main each side of the pump riser junction.

3. At each cross-over connection junction to the ring main.

4. Where the ring main penetrates a watertight bulkhead.

5. In the ring main each side of the branch to the magazine spray system.

10.3.5 Where the HPSW system is to be used for firefighting purposes, the supplies are to be led through vertical distribution lines directly from the horizontal ring main to the upper deck levels.

10.3.6 Shore and ship to ship connections to the HPSW ring main are to be provided port and starboard on the weatherdeck – one pair forward, the other aft, i.e. a total of four connections. For NS3 category ships with a breadth not exceeding 10 m, a single connection forward and a single connection aft will be acceptable.