Assessment of Current Offshore Supply Vessel Capabilities for Crew Transfer Operations in the Flemish Pass

Abstract

The Flemish Pass is a region off the coast of the province of Newfoundland and Labrador in which large oil discoveries have been made in recent years, making it a promising site for future offshore oil and gas developments. The site is located approximately 200 kilometers North-East of the currently producing Jeanne D’Arc Basin. This results in some additional challenges, including: higher waves and rougher seas on average, longer transit time from shore to any potential production facilities, and an increased risk of sea ice. Crew transfers from Offshore Supply Vessels (OSVs) to current production platforms offshore Newfoundland and Labrador are typically accomplished with a FROG-6 personnel-transfer capsule lifted by a platform-board crane. In current practice, for fixed platforms, this is only done when there is a Significant Wave Height (Hs) of 4.0 m or less, regardless of the OSV being used. In the winter months, this general-purpose approach does not allow for an acceptably high operational fraction of time in which crew transfers could be completed in the Flemish Pass. The FROG-6 capsule has designated operational limits based on the relative velocity between the capsule and the vessel deck, which will vary based on ship size, loading condition, and sea-state. Considering this, a series of geometrically similar OSV hull forms are created to represent the range of currently operating vessels. The developed models are between 70.0–90.0 m long, have a maximum breadth between 17.0–22.0 m, and block coefficients ranging from 0.65–0.79. Using ShipMo3D, a potential flow / panel code seakeeping solver, a 20 minute time history of ship motions is determined for all the modelled OSVs, across the range of sea-states realistically expected in the Flemish Pass. Then, a MATLAB script is used to transform these motions into deck velocities. From these results, the operational limits for crew transfer can be re-defined as a function of ship size, loading condition, and sea-state. This results in higher operability percentages than those achieved from using the flat wave height limit alone, with relatively large variations between differently sized and loaded ships. Further work must be done to officially implement new limits, such as: analysis of additional wave period and height combinations, further analysis of the time between limit exceedances, computational fluid dynamics simulations, “smart crane” modelling, and/or full scale sea trials.