System of Systems

A ship in simpler terms is a plant, or system, consisting of various smaller systems working together in harmony. Think about the human body as an example of an overall system consisting of various sub-systems. Without these sub-systems, a human body will not be able to function affectively, reliably and efficiently. The same can be said of a ship. A ship can therefore be defined as a “system of systems”. A “system of systems” can be further defined simply as:

A collection of dedicated systems (sub-systems) that pool their resources and capabilities together to create a more complex system, which offers more functionality and performance than simply the sum of the constituent systems.

It is easy to grasp the concept, for example, say a ship is outfitted with a specific propulsion system. What is the use of the propulsion on its own? Frankly, no use at all.  Without the ship’s hull, as well as all the other supporting systems for the propulsion system i.e. fuel, oil, cooling water and control systems, the propulsion system will not be able to do anything!

The only way of achieving a complete System of Systems, is by means of Systems Integration.

System Integration

Systems integration is required to ensure that all the sub-systems onboard a ship or plant is perfectly paired. System Integration can be defined as follows:

System Integration is the bringing together of the component sub-systems into one system and ensuring that the sub-systems function together as a complete System of Systems.

It is therefore important that all sub-systems can operate in unison and correctly integrate and interface with each other where required.

System Categorisation in the Marine Industry


The ship system, its sub-systems and sub-sub-systems can be placed in various categories to make the life of the Marine Engineer and Naval Architect much easier when working on specific systems and ensuring that all systems that forms part of the ship is properly addressed.  This is called System Categorisation, of which you have already seen an example of the SFI and ESWBS systems categorisation methods.

  • Propulsion Systems
  • Auxiliary Systems
  • Control & Management Systems

 These three categories listed above, in terms of the onboard ship systems, is still at an extremely low level, and needs to be broken into much higher levels to reflect greater detail, especially in the ship building industry. As an example of the depth of these levels, a collection of sub-systems and components of a ship is shown in Table below. These are some of sub-systems and components that you will find listed in their specific SFI Group or System Category:

Example List of Ship Systems and Components

  • Engines/Motors
  • Turbines
  • Gearboxes
  • Boilers
  • Heat Exchangers
  • Pumps
  • Valves
  • Filters
  • Strainers
  • Switchboards and Cabling
  • Compressors
  • Distillation
  • Separators
  • Sewage Treatment
  • Condensers
  • Lifting Appliances
  • Pressure Vessels
  • Pipe and Hoses
  • Exhaust
  • Controllers and Instrumentation
  • Refrigeration
  • HVAC
  • Mooring
  • Anchor Handling
  • Stabilising
  • Thrusters
  • Safety and Survival
  • Shafting and Propellers
  • Steering Gear
  • Materials

Standard Hierarchical System Breakdown

By making use of a standard hierarchical breakdown of the various systems that constitute a ship, excluding propulsion and hull, you will be able to note all the aspects that must be addressed and on-board systems considered.

Level 2 System Categories for a Level 1 Ship System

Level 3 and 4 Systems of the Propulsion Support Level 2 System

Level 3 and 4 Systems of the Safety Level 2 System

Level 3 and 4 Systems of the Hotel Level 2 System

Level 3 and 4 Systems of the Cargo Level 2 System

Level 3 and 4 Systems of the Facilities Management Level 2 System

Level 3 and 4 Systems of the Environmental Control Level 2 System

It is difficult to categorize the myriad of components and sub-systems of a ship in the three categories mentioned earlier, thus methods of system categorisation and groupings were developed to ensure that a standardised categorisation system (breakdown structure) is used, either internationally, or shipyard specific.

As mentioned earlier in the Learner Guide the SFI groups 1 – 8 are most widely used commercially, while the ESWBS groups 000 – 900 are used in Naval applications, but still remains commercially useful.

Work Breakdown Structures or System Categorisation standards other than the SFI and EWSBS groups that can also be used are a specific Shipyard’s Specification, the Classification Society Master List or the grouping used by ship Maintenance Management Systems:

Shipyard Specification: Shipyards tend to develop their own breakdown and/or categorisation structures to suit their needs, as well as their configuration management systems.

Classification Survey Master List: A structure specifically used by Classification Societies.

Maintenance Management System: Maintenance Management Systems almost always incorporate a numbered breakdown structure. This numbering structure might be the same as any of the structures mentioned above, or may have its own unique breakdown structure numbering/grouping.

The SFI method of system categorization is the most widely used. Due to its wide user-base, this specific categorization method will be discussed in greater detail in the following paragraphs and figures. As stated earlier, the SFI structure is broken down in sub-structures from 1 to 8.  We will only focus to a depth of three levels per sub-structure, as you can go down more than 6 levels up to “nuts and bolts”.

The level 2 structures from 1 – 8 is listed below from left to right. 1 Being “General” and 8 being “Ship Common Systems”. The Ship is considered as the Level 1 system. Sub-structure 1 “General” is mostly aligned with administrative procedures when a ship specification is written.  As this learning opportunity is purely focussed on the technical aspects of Marine Engineering and Naval Architecture, no further detail will be provided on “General”.

SFI Ship Level 1 and Associated Level 2 Categories, 1 to 8

SFI Level 3 Systems of SFI Level 2: Group 2 – Hull

SFI Level 3 Systems of SFI Level 2: Group 2 – Equipment (Cargo)

SFI Level 3 Systems of SFI Level 2: Group 2 – Equipment (Ship)

SFI Level 3 Systems of SFI Level 2: Group 2 – Equipment (Crew/Passenger)

SFI Level 3 Systems of SFI Level 2: Group 2 – Machinery (Main Components)

SFI Level 3 Systems of SFI Level 2: Group 2 – Systems for Machinery

SFI Level 3 Systems of SFI Level 2: Group 2 – Ship Common Systems

System categorization is extremely helpful when developing a ship specification and for the various systems of the ship that requires consideration during the ship design process.

System categorization is also extremely useful in other aspects, for example:

  • Maintenance Management – A breakdown structure is required to ensure that each part is suitably linked to a specific system for the purpose of recording operating hours, to group maintenance items and spares, and to suitably structure maintenance periods.
  • Configuration Management – Technical documentation is usually grouped in accordance with the categorisation structure used by the Shipyard/Marine Engineering company. This allows the referencing of a document/drawing by each specific category number already assigned to a specific system.
  • Engineering Change Management
  • Financial Management


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