Vessel Performance: Dynamic Positioning capabilities for superyachts

Dynamic Positioning systems are now featured on many large yachts but are not widely understood. James Calver and James Roy, BMT Nigel Gee, explains

James Roy James CalverDynamic Positioning (DP) systems are a mature and well-proven technology. The superyacht industry has embraced DP as a concept, and many large yachts now feature some level of station-keeping capability. However DP is not widely understood within this industry beyond the basic principles, capabilities are frequently over-specified and the resulting impact on the level of installed power is often severe.

This article aims to provide a background to the principles of basic station-keeping, typical thruster arrangements, and how DP is used in practice. Also discussed are the various fundamental methods of controlling the degree of DP capability, along with the impact of implementation on the vessel’s design.

Since its first use in the 1960s, the field of Dynamic Positioning has exploded in terms of complexity, reliability and uptake. In recent years some level of station-keeping capability has come to be expected of most large yachts. The level of station keeping specified, and thruster/propulsion system utilised, must be done with careful consideration to minimise the impact on the vessel’s overall function as a piece of luxurious real estate.

One capability of a DP system is to ‘park’ a vessel at sea without an anchor, and have it remain in a fixed position by using computers to automatically control the thrusters. However this is a very energy intensive operation and uses a lot of fuel. This functionality only really comes in useful in deep water, when anchoring would not be feasible. A more common use of the system is in conjunction with an anchor to keep the vessel headed into an incoming swell in order to reduce roll motion or swing range.

For the sake of clarity it is important to make the distinction between DP and station keeping. DP refers to the process whereby a computer controls the various thrusters and propulsors installed on the vessel to result in the desired thrust vector, in response to a joystick input from the bridge. DP systems account for external forces acting upon the vessel, such as wind, waves and current. One common feature of a DP system is a station-keeping function. This is the vessel’s capability to react to external loading to maintain a certain position and heading.

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