| This vessel was placed on long-term charter to Imperial Oil Ltd. for service in the Beaufort Sea and the Mackenzie Delta. In 1984 this vessel was owned by Roylease Ltd., Toronto ON. The vessel was designed and constructed for Arctic conditions. The hull was built of steel plate with a weight-saving aluminum superstructure. A helipad was also constructed on the after-deck enabled easy access by air for technical and company staff to the vessel. Other design features included a blunt bow in anticipation of barge-pushing on the Mackenzie Waterway after the conclusion of the initial charter. An elaborate system of gear for carry-out the seismic surveys included lowering twelve sleeve-exploders mounted in four groups of three (two groups on each side of the vessel.) In shallow water the exploders were towed suspended just above the seafloor surface. In deep water the exploders were towed about 22' below the water's surface. A signal is transmitted to the bottom of the ocean by simultaneous explosions created in the 12 sleeve-exploders of a mixture of oxygen and propane gases. The gases were stored in pressurized tanks mounted on the stern deck. The gas mixture was introduced to the exploder and ignited by a sparkplug in each one with the ignition timing centally controlled at the technical instrumentation room. At the same time a 120 channel marine streamer cable 1.5 miles long was unrolled from a cable drum and towed behind the vessel. The cable was covered with a polyurethane jacket for protection and filled with oil. The cable contained 120 electronic arrays each 60' in length and each containing 20 hydrophone sensors spaced at 3' intervals. During shallow water testing (in less than 25' depth) the vessel would come to a full stop while the arrays and cable fell to rest on the seafoor. The exploders would then fire and data collected before proceeding to the next location. As long as the bottom material was uniform in configuration and of a smooth composition the array was safe from snagging and breakage. In deep water the array was towed at a constant depth of about 90' with the crane equipment constantly controling and adjusting the depth. The sound emitted from the exploders wqas transmitted to the bottom and the time-delayed echo interval recorded in the sensors located in the array. The delay of echo return was determined by the depth and composition of the various layers of geological strata encountered by the signal. The data, when interpreted by techicians and engineers, would give a picture of the make-up of the ocean floor and indicate the likely locations, if any, of oil or gas bearing geological structures. One of the key factors in seismic exploration is that the engineers must know the exact position of the sip at any given moment in the charting of the bottom. Technicians take radio transponder beacons ashore prior to the bottom surveying and establish ground control points. Once these points are established the engineers can triangulate, electronically, on these points and determine precise coordinates of the ship. The triangulation enables the plotting of exact and precise data for future analysis and interpretation. Decisions which will determine the locations for the drill ships to spud-in the bit are made based on the interpretation of this data. The Arctic Surveyor was using a then state-of-the-art Motorola Range Position monitoring system for work close to shore and a Shoran system for offshore work. |
