Managing operational expectations

Many design choices for floating offshore installations are driven by expected operational performance. Design studies help to understand operability limits, but real life performance depends on mariners and agreements between owner and operator. MARIN’s clients increasingly use Full Mission Bridge Simulators to bring all parties and their expertise together to establish operational procedures and evaluate weather limits.

A recent offshore oil project in South America gives a good example of this. The first phase development includes a subsea production system and a Floating Production, Storage and Offloading (FPSO) vessel designed to produce over 100,000 barrels of oil per day. The directional weather conditions allow for a spread moored FPSO, maintaining a heading into the waves, wind and currents.

Arjan Voogt

Offloading is planned with conventional oil tankers in a tandem loading configuration. The vessels are connected by a hawser, which assumes a direction relative to the FPSO and the tanker. Several tugboats are available for the operation to handle the hose and maintain a tension in the hawser and thus, a safe separation distance between the tanker and the FPSO. The tugboats can influence the heading of the tanker, which changes the environmental loads on the tanker and the resulting loads in the hawser. Many different solutions are possible on paper, but not all of them are practical to mariners.

Numerical simulations First the limiting weather conditions were selected from a large amount of numerical simulations in which the tugs were controlled with autopilots. As forces of wind, wave and current sometimes cancel each other out and at other times align to cause large loads in the hawser, associated weather conditions had to be studied. This resulted in a strong focus on probabilities and mathematics.

To combine this hydrodynamic knowledge with nautical experience and to involve both owner and operator in the conversation about practical limits, selected weather conditions were evaluated with manoeuvring simulations.

The Full Mission Bridge Simulator in MARIN’s Houston office provided a great communication tool for mariners and designers. This cooperation provides feedback from mariners, which is input into the design and improves the operational guidance to the field.

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