Dynamic Positioning System
Failure Mode & Effect Analysis (FMEA) is the analytical study of a system's integrity in the midst of a failure. It is commonly applied to systems that cannot fail even when several critical components in the system have. In the maritime sector, FMEA is conducted on a 5-yearly basis to determine the single-point-failure tolerance of the DP system of vessels. DP system works as an autopilot mechanism that the crew relies on to maintain the vessel's position whilst they can focus on other critical activities. These activities are usually done in crowded waters where losing position can lead to catastrophe. FMEA is integral to the reliability of the DP system and a critical component for charterer in evaluating the vessel's DP worthiness.
Dynamic Positioning (DP) is a computer-controlled system that allows vessels to hold position and heading in a location that is otherwise too deep to launch anchors. DP is achieved by integrating the control units of all thrusters onboard the vessel into a single computerized system. The system, commonly known as the DP system, uses a carefully constructed algorithm to provide a continuous and responsive thrust vectoring on all three degrees of freedom of the vessel (yaw, surge, and sway) to keep the vessel in the same position and at the same heading. Without the DP system, offshore activities such as personnel transfer, subsea pipe-laying, and offshore construction will be risky if not impossible. Currently, DP systems can be categorized into three classes defined by the International Maritime Organization(IMO).
DP Equipment Class 1 (DP-1)
A vessel classed under the IMO DP Equipment Class DP-1 or its equivalent is equipped with a DP system that may fail after a single point failure. The vessel has adequate thrusters and sensors in place for a DP system to monitor and keep the vessel in position and at the same heading for prolong period of time. However, the vessel lacks redundancy and as such a loss of any DP-critical component may render the DP system inoperable.
DP Equipment Class 2 (DP-2)
A vessel classed under the IMO DP Equipment Class DP-2 or its equivalent is equipped with a DP system that shall not fail after a single point failure. This can be achieved by having all DP-critical components duplicated and/or providing them with multiple power supplies. On top of that, the vessel's power system, fuel oil system, lubrication oil system, cooling system, compressed air system, and the HVAC system have to be redundant as well.
DP Equipment Class 3 (DP-3)
A vessel classed under the IMO DP Equipment Class DP-3 or its equivalent is equipped with a DP system that is as redundant as what is defined in DP equipment Class 2. In addition to having DP-critical equipment duplicated, these redundancies and their essential complimentary systems shall also be separated by an A-60 class fire shielding and kept in their respective water tight compartment such that no flooding or fire in a single compartment shall render the DP system inoperational.