Section 147.831 - Holstein Truss Spar safety zone(a)Description. Holstein, Green Canyon 645 (GC 645), located at position 27°19'17" N, 90°32'08" W. The area within 500 meters (1640.4 feet) from each point on the structure's outer edge is a safety zone. These coordinates are based upon North American Datum 1983.(b)Regulation. No vessel may enter or remain in this safety zone except the following: (2) A vessel under 100 feet in length overall not engaged in towing; or(3) A vessel authorized by the Commander, Eighth Coast Guard District.CGD08-03-028, 69 FR 6147 , Feb. 10, 2004