Motion compensating floor system and method

A method for compensating for relative motion between a vessel, a heave floor unit, and a subsea riser, the method comprising:

• attaching the heave floor unit to a deck or a hull of the vessel, the heave floor unit comprising:
• a first floor that is attached to the deck or the hull, a second floor, and a plurality of hydraulic cylinders connecting the first floor to the second floor;
• a bearing retainer attached to the second floor;
• a spherical bearing provided between the second floor and the bearing retainer, wherein the spherical bearing includes a central opening therethrough for the riser to allow angular movement of the riser relative to the heave floor unit;
• an insert bearing sleeve at least partially located inside the central opening of the spherical bearing;
• and
• a slip bowl attached to the insert bearing sleeve,
• wherein each of the first floor, the second floor, the bearing retainer, the insert bearing sleeve and the slip bowl have an opening therethrough that is aligned with the central opening of the spherical bearing;
• inserting the subsea riser through the central opening of the spherical bearing and the opening of the first floor, the opening of the second floor, the bearing retainer, the insert bearing sleeve and the slip bowl;
• and
• actuating the plurality of hydraulic cylinders in response to motion of the vessel relative to the second floor, and in response to motion of the heave floor unit relative to the angular movement the subsea riser.