Evaluating criteria for DP vessels

The paper presents the evaluating criteria for DP vessels. A few persons tried to give a simple tool for comparing the station keeping capability between different ships. It was started in the seventies when most vessels claiming to have a DP system would be carried away by the current only (the limit was 1.5 up to 2 knots). Mainly DNV and ABS, next IMO prepared the calculating methods for DP system evaluation during the design process to receive the DP class 1, 2 or 3. The regulations may help but it’s still only rough estimate. One of them is the most popular. It is the capability plot presenting at preliminary the polar diagram with number envelops, showing the vessel’s capability to keep position or heading with a certain combination of thrusters in operation. The number, type, total power (or thrust) and location of thrusters are vital for estimating the DP capability from the propulsion system. The other equipment is only accessories assisting the DP system. At the end the sea trial may check and confirm the DP class of the vessel. The real capability for station keeping will be verified during normal operation, essentially during emergency situations like electric network faults, propulsion system failure up to damages and fire. It is needed some indexes or parameters during the design process to avoid serious faults. The paper is a probe of becoming familiar with chosen criteria.