Computer based marine systems on ships fall into two categories: those essential for the safe operation of the ship and those that are not critical to the ship and its safety. These are also differentiated by the classification societies and IMO by requiring certification based on IEC 60945 for the former and lesser controls for the latter.
What systems are critical to the safe operation of the ship? In general these are the primary navigation systems, propulsion systems and alarm and safety systems, plus any sub systems that are required for these to function correctly.
- Navigation equipment includes the sensors used to determine position of the ship, its progress and activity near the ship. These include radar, GPS, compass, log, depth sounders, and of course charts in the form of ECDIS, as well as the systems combining this information for passage planning and communication with other vessels and the shore.
- Similarly propulsion systems include propulsion control (including dynamic positioning), machinery control and monitoring essential systems like main engines, cooling systems, electrical generation and distribution.
- Finally safety systems cover alarm systems, fire detection and suppression, watertight compartment monitoring and control, and evacuation systems. You could also add stability systems and loading computers.
Certification of these systems, intrinsic of every ship computer, ultimately requires proving they operate correctly at all times and in all circumstances. This requires approval by the relevant classification society, e.g. DNV 2.4, for the complete systems, not just the marine pc.
There are two main approaches to designing and developing systems to meet classification society approval. The first involves using ready certified components such as certified marine computers, so the hardware and software components are known to be compliant, minimising the risk of the complete system failing to achieve the required approval.
The second uses components that are not individually certified to marine standards, eg IEC 60945, and the ultimate certification is achieved solely for the completed system. This is a more risky approach as one component falling short of the requirement will cause failure and delay in the approval of the whole system, adding significantly to the time and cost of the system.
Of these two approaches the first, using certified hardware, allows the system development schedule to be planned and costed with a high degree of certainty. The alternative, using unapproved computers, is much more uncertain and carries high levels of risk to both the programme schedule and cost. Consequently it is prudent to use marine computers certified to IEC 60945, IACS E10 and DNV 2.4, such as those available from Captec when developing key ship systems. But the decision is ultimately up to the system developer, and there are still a few who are prepared to take the risky route.
Next time I will take a closer look at the certification requirements for marine computers.