Abstract At-sea managers typically make operational decisions based on less-than-possible knowledge of their present and probable near-future situations. To alleviate this deficiency for floating systems, a new forecasting approach has been developed that utilizes computerized dynamical models of vessels and spectral models of ocean wave fields. This paper discusses the application of this approach to support operators in the North Sea. The North Sea Spectral Wave Model is based on state-of-the-art knowledge of wind-wave evolution, while the vessel models are based on modern dynamical analyses. Together, they are incorporated into an operational forecasting system that estimates the gross effects of the seaway on vessels before the fact. This approach provides offshore supervisors with the information necessary to predict properly their ability to execute upcoming work and thus to achieve more economic offshore operations. Introduction The offshore oil and gas industry has steadily applied new technological advancements to design offshore systems. These improvements in hardware and operational techniques have been motivated by the inherent difficulties of working offshore and by the continual economic pressures of exploration and production. The industry has been slower, however, to incorporate new technologies into the actual real-time decision-making process at sea to plan and execute operations as they occur. The industry generally has preferred to rely on traditional techniques based on the personal, subjective experiences of senior offshore personnel to make operational decisions such as committing to work on the BOP, stopping operations due to possible bad weather, etc. Today's technologies, particularly in the fields of environmental forecasting and the dynamical analysis of floating systems, have therefore not generally been employed at sea to achieve more economic offshore scheduling. As a result, at-sea managers typically make decisions based on less-than-possible knowledge of their present and near-future operational situations. A new prediction approach has been developed to help alleviate this deficiency for floating systems such as semisubmersibles, drillships, derrick barges, etc. At the heart of the approach are computerized dynamical models of the vessels and spectral models of the ocean wave fields. The wave models are based upon state-of-the-art knowledge of wind-wave generation, propagation, and decay, while the vessel models are based on modern dynamical analyses. Together, they have established a foundation for providing offshore supervisors with the information necessary to predict properly their ability to execute upcoming work. By applying this forecasting approach, operators can now anticipate their best mode of operation in advance and thereby schedule accordingly. Decisions thus can be made objectively to maximize the economic return for an overall operation. This paper discusses the application of this approach to support operators in the North Sea. In-house development of the forecasting system began in 1975 with the sponsorship of Burmah Oil Development Limited. The initial system became operational in 1976, and since then it has provided predictions on a continual basis.