Section 7 Extract from the Naval Ship Rules

7.1 General

The following text is reproduced from Vol 2, Pt 1, Ch 1 General Requirements for Classification of Engineering Systems in the Rules and Regulations for the Classification of Naval Ships, January 2016. It is provided to enable easier understanding of the definitions for Engineering System, and Relevant Hazard, see Ch 1, 5 Definitions .

Section 3 Engineering system designation

3.1 Categories

3.1.1 For the purpose of classification, an Engineering System is defined as any system that may be installed in a ship where such a system comprises one or more sub-systems or components. For the purpose of determining the appropriate assessment process for engineering systems in naval ships, there are three categories:

Mobility.
Ship Type.
Ancillary.

3.1.2 Mobility category engineering systems are those systems installed in order for the ship to proceed on operations and are necessary for:

Maintaining the watertight and weathertight integrity of the hull and spaces within the hull.
The safety and reliability of propulsion, steering and electrical systems.
The operation and functioning of emergency machinery and equipment.

3.1.3 Ship Type category engineering systems are those systems installed in order for the ship to carry out its in-service purpose and are necessary for:

The operation and functioning of the systems and equipment installed for purposes relating to the ship’s in-service purpose excluding the operation and functioning of military systems.
The operation and functioning of emergency machinery and equipment.

3.1.4 Ancillary category engineering systems are all systems other than Mobility category or Ship Type category, failure of which may compromise the provisions of Classification and are necessary for:

The provision of basic conditions on board for the carriage of stores, fuels, equipment and personnel when the ship is at sea, at anchor, or moored in harbour.

3.1.5 Engineering Systems are to be assigned to the appropriate category taking into consideration the:

ConOps for the vessel (see Vol 1, Pt 1, Ch 2, 2.2 Definitions 2.2.17);
criteria in paragraphs Vol 2, Pt 1, Ch 1, 3.1 Categories 3.1.1 to Vol 2, Pt 1, Ch 1, 3.1 Categories 3.1.4 for Engineering Systems and the Mobility, Ship Type and Ancillary categories;
dependency of Mobility or Ship Type engineering system upon other systems or services for their correct operation (e.g. if the propulsion plant’s electronic control systems is cooled by chilled water, then the chilled water system is to be considered critical to the propulsion plant’s function and assigned to the Mobility category);
military systems and damage control arrangements relating to the Ship Type are to be stated where applicable.

3.1.6 Services such as the following are considered necessary for minimum comfortable conditions of habitability:

cooking;
heating and cooling;
domestic refrigeration;
mechanical ventilation;
sanitary and fresh water.

3.1.7. Services such as the following, which are additional to those in Vol 2, Pt 1, Ch 1, 3.1 Categories 3.1.5 and Vol 2, Pt 1, Ch 1, 3.1 Categories 3.1.6, are considered necessary to maintain the ship in a normal seagoing operational and habitable condition:

hotel services, other than those required for habitable conditions;
thrusters.