Primary Essential Services are those which need to be in continuous operation for maintaining propulsion and steering.
Some of them are as follows:
1) Steering gears.
2) Pumps for controllable pitch propellers.
3) Scavenging air blower, fuel oil supply pumps, fuel valve cooling pumps, lubricating oil pumps and cooling water pumps for main and auxiliary engines and turbines necessary for propulsion.
4) Ventilation necessary to maintain propulsion.
5) Forced draft fans, feed water pumps, water circulating pumps, vacuum pumps and condensate pumps for steam plants on steam turbine ships, and also for auxiliary boilers on vessels where steam is used for equipment supplying primary essential services.
6) Oil burning installations for steam plants on steam turbine vessels and for auxiliary boilers where steam is used for equipment supplying primary essential services.
7) Azimuth thrusters which are the sole means for propulsion/steering with lubricating oil pumps, cooling water pumps, etc.
8) Electrical equipment for electric propulsion plant with lubricating oil pumps and cooling water pumps.
9) Electric generators and associated power sources supplying primary essential equipment
10) Hydraulic pumps supplying primary essential equipment.
11) Viscosity control equipment for heavy fuel oil.
12) Control, monitoring and safety devices/systems of equipment for primary essential services.
13) Fire detection and alarm system.