Patent ID: 8579547

Claim:
Vessel having an elongate shape, and being moored to the sea bed in a substantially fixed orientation, the vessel comprising: skirts extending along longitudinal sides and shorts sides of said vessel, near keel level, said skirts having such a width that the natural roll period of the vessel is above a predetermined period, the natural roll period of the vessel without the skirts being below said predetermined period, said skirts are each constructed to provide a volume that displaces water, wherein the vessel is substantially rectangular in shape, the vessel comprising a central well and a drill string and/or riser extending through the well, the vessel being anchored to the sea bed in anchor points situated at a distance from the well on the hull of the vessel in a spread moored manner, wherein a length-to-width ratio of the vessel is at least 2, the skirts having over their length a substantially constant width of at least 5% of the width of the vessel near keel level, and extending over at least 60% of the length of the vessel, wherein a volume of one of said skirts is at least 2% of the total volume of the vessel, and wherein the draft of the vessel is not greater than 30 meters.