Purpose

This document has been generated by the MTS DP Technical Committee and has been provided to industry as a guidance document to aid in the design of DP vessels.

This document is not meant to replace any rules, regulations or guidelines that are in existence. It is a compilation of experiences, practices and information gleaned from various sources in industry, some of which are not in the public domain. It is expected that compliance with applicable class rules will be ensured.

It is acknowledged that DP Class notation is governed by class rules which cover DP equipment and addresses redundancy requirements. However, these rules do not address the industrial mission of the vessel nor the overall performance and operational capability. Consequently vessels designed to obtain a DP Class Notation alone may not achieve the post worst case failure capability that could potentially be achieved by establishing and adopting philosophies that minimize loss of positioning capability after failure and enhance reliability.

Note: LRS and DNV offer a means to compare DP vessel performance through the use of PCR and ERN numbers.

This is not intended to be an all encompassing document covering all aspects of DP vessel design. It attempts to provide guidance on a number of themes which have not been adequately defined by DP class rules or are subject to interpretation. Incorporating the guidance provided in this document during design should result in a vessel with enhanced capability to perform its industrial function and which meets class rules for the desired DP Class Notation.

Enhanced vessel capability as implied in this document means a more fault tolerant/fault resistant DP system which minimizes loss of positioning capability post worst case failure. This in turn translates into greater operational uptime and the ability to carry out its mission within a larger operating envelope.

The focus areas of this document have evolved from industry experience of technical failures. Addressing these vulnerabilities during design will result in a robust vessel capable of conducting its industrial mission. Exposure to environmental conditions is addressed by focusing on capability and sizing of thrusters and power plants. Technical failures are addressed by designing fault tolerant and fault resistant systems. Some technical faults require operator intervention to prevent escalation. Ergonomics and ‘decisions support tools’ aid effective operator intervention.

Implementation of the Guidance during design phase rather than later in the life cycle is expected to lower the cost of a “fit for purpose” DP vessel.

The guidance provided in this document is not directed at any particular category of DP vessel. It is intended to apply to any Class 2 or Class 3 DP vessel operating in support of offshore oil and gas activities. The principles may be implemented as appropriate on Class 1 DP vessels. Examples include MODUs, MOUs, construction and logistics vessels where dynamic positioning is used for, or aiding, station keeping.