DP states for Dynamic Positioning and the DP system is defined as:

The DP system consists of components and systems acting together to achieve reliable position keeping capability.


From this definition, it is clear that the DP system includes some parts called components in the number of seven, as shown in, which shall be remembered:

DP elements


Components of DP System: Overview and Functional Description.

Only proper functioning of all these components is able to ensure reliable functioning of the whole DP system. Upon arrival on board, it is necessary to study each component individually (its structure, layout, disadvantages, etc.) and monitor its functioning continuously during DP operation.

While speaking about DP class 2 and 3 vessels, duplication of each component is considered – a so-called Redundancy. It is, therefore, necessary to have clear understanding of the DP system in order to answer the question, if redundancy is provided, i.e. if the DP system complies with class 2 or class 3.

Before continuing to study some peculiarities of the DP system, it is necessary to understand the basics and principles of its work. The main international guideline for the vessels with the dynamic positioning system is IMO MSC Circular 645. The given above definition of the DP system comes from Circular 645 and is just an initial one. Later, to understand the concept of DP, it shall be considered from different angles and more terms shall be provided accordingly.

Circular 645 came into force in 1994. 20 years later, it was decided to make some amendments and, as a result, in June 2017 MSC.1/Circ.1580 was released. This new Circular is an updated and amended version of the previous one and contains basic requirements of the industry at present. The mentioned above definition can be found in Circular 1580 as well.

Considering this, the question may arise: which Circular shall the vessel and the system comply with? It is recommended that vessels built from the 1st of July 1994 until the 9th of June 2017 shall comply with Circular 645, while vessels built from the 9th of June 2017 and later shall comply with new Circular 1580. However, it is advised that Section 4 of the new Circular shall be applied to new and already built vessels.

Definitions containing in the amended Circular will be referred in this book. Similar definition of the DP system can be found in previous Circular. One of the difference is that meaning “to maintain a position” in Circular 645 is defined as “to maintain a position and/or heading” in Circular 1580 respectively. 

The previous Circular is mentioned as subject matter tests and competence assessments might still refer to Circular 645, however questions based on Circular 1580 may be encountered and it is necessary to be ready for any variants.

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Risk assessment matrix

A TRA is a formal risk assessment for a specific task

It breaks the task down into steps, usually derived from the Work Instruction, and then:

  • analyses the potential hazards for each step,
  • records the existing controls already specified by procedures,
  • and describes any additional controls required for each step to ensure the risks remain acceptable.

It is designed to be referred to before conducting the task as a reminder of the potential hazards and necessary controls.

Every task that is conducted regularly should have a TRA written for it.

If about to conduct a non-routine task that includes potential hazards, a TRA should be created if one does not already exist.


As Low as Reasonably Practicable (ALARP): BGP Offshore has a legal duty to reduce risks to a level that is As Low as Reasonably Practicable (ALARP). Risk is shown to be ALARP when it can be demonstrated that the risk of activity has been reduced to a level acceptable to stakeholders. To reduce a risk to a level “as low as reasonably practicable” represents the point where the time, trouble, difficulty and cost of further reduction measures become unreasonably disproportionate to the additional risk reduction obtained.

In other words – no task is risk free; ALARP allows focusing of efforts on where they will have the most impact.

Consequence: Outcome of an event affecting objectives.

Hazard: A hazard is any object, situation, or behavior that has the potential to cause injury, ill health, or damage to property or the environment.

Hazard Effect: The consequences (harm) if a particular hazard is realized. Hazard effect in this context covers injury to people, ill-health or damage to property, equipment or the environment.

Initial Risk: The initial risk rating is based on the realistic outcome (severity) identified in the Hazard Effects and the likelihood of the Hazard Effects occurring, with all the BGPO existing controls in place. (E.g. A1 (Low), B4 (Medium), C5 (High)

Likelihood: Chance of something happening. This is targeted when trying to reduce the event from happening.

Residual Risk: Risk remaining after any additional control measures being applied which are excluding from BGPO existing controls. (E.g. A1 (Low), B4 (Medium), C5 (High)

Risk: The product of the chance that a specific adverse event will occur and the severity of the consequences of the event.

Severity: The numeric value assigned to a consequence.