163 Preliminary Report

Site 990

The site beacon was dropped by GPS coordinates at 2145 GMT on 20 September, after dynamically moving the vessel from Site 989. A standard RCB nine-collar BHA was made up with a C-4 bit and an MBR. Because the sediment section of this site had been cored on Leg 152, the plan was to drill through most (180 m) of the sediments and core from this depth into basement.

Hole 990A

The hole was drilled to 41 mbsf before excessive heave generated by a sudden gale forced us to come out of the hole for 3hr. We reentered the hole at 0645 GMT, 21 September, and advanced to 27 mbsf before drilling was stopped again to allow a large iceberg to clear the drilling area.

A free-fall funnel was then deployed to ensure that any progress would not be lost if a sudden exit were required because of ice or weather. Drilling resumed and deepened the hole to 45 mbsf when another iceberg approached, forcing the driller to lift the bit to 10 mbsf. The 70-m-high iceberg passed within 1.2 nmi of the vessel, moving south at 1.1 kt. Two more hours of washing and reaming were required before advancing the bit back down to 45 mbsf.

By 0515 GMT on 22 September, the hole had been deepened to 63 mbsf. At this time, the mates on the bridge suddenly detected a large bergy bit very close to the vessel. The drill floor was advised to pull out of the hole and the vessel was immediately offset to starboard. A second growler was then observed within 10 m of the vessel. The ship changed heading to meet this piece of ice head-on, which bounced off the port bow and then passed the vessel on the port side, without causing damage. The predominantly low profile of the ice, combined with the rough sea state, made it difficult to detect growlers and bergy bits by radar or with searchlights.

After waiting on ice for 15 min, the bit was pulled to the surface and a mill-tooth tricone drilling bit was made up with an MBR. It was expected that the mill-tooth bit would penetrate the 180 m of sediment much faster than a coring bit.

The second reentry of the hole was accomplished at 1530 GMT on 22 September. The hole was washed and reamed from 10 to 134 mbsf, after which the hole was drilled ahead to 182 mbsf. After flushing the hole with mud, the bit was tripped to the surface to change to a coring bit.

A new C-4 bit was made up with a nine-collar BHA and run back to the bottom of the hole, and at 0322 GMT on September 24, the third reentry of the hole was made. The hole was washed and reamed from 19 to 181 mbsf, after which the wash barrel was retrieved and a core barrel dropped. Finally, at 0900 GMT, coring was initiated in Hole 990A. After a first core containing conglomerate and drilling rubble was retrieved, coring had to be terminated because of a developing storm. The drill string was pulled out of the hole, with the bit clearing the seafloor at1600 GMT that day. A Force 10 storm from the north prevailed during the afternoon and late into the evening, with wind gusts as high as 60 kt and 20-30-ft seas. By 1100 GMT the next day, the winds had died down and the large swell was abating. Reentry of the hole was delayed for nearly 5 hr to repair a defective TV camera on the vibration-isolated television (VIT) system.

Medical Evacuation

During this storm, a lost-time accident occurred involving crane operator Andy Fitzmorris. One half of a free-fall funnel was secured to the starboard main deck under the drill floor with a new 3/8 in. cargo chain. A large wave came over the side, hit the free-fall funnel, broke the chain, and washed the free-fall funnel into the aft moonpool tugger. Andy and two other men were trying to resecure the free-fall funnel when another wave came over the side. Andy was hit by the wave and lost his footing while holding on to the chain to avoid being swept into the moonpool, which resulted in the dislocation of his shoulder and torn ligaments.

A medivac helicopter arrived the next day 25 September at 1505 GMT and transported Andy to Ammassalik, Greenland, from where he was flown to Iceland for medical treatment. This incident broke a string of 1368 days without a lost-time accident.

At 1700 GMT on 25 September, the hole was reentered, and after extensive reaming of the bottom section (181-191 mbsf), coring was resumed in Hole 990A. Rotary coring advanced routinely to 260 mbsf, where the drill pipe got stuck. After the string was picked up to 249.6 mbsf to retrieve Core 163-990A-12R, the hole began to pack off around the drill string and circulation and rotation were lost. After restoring rotation and working the pipe up the hole for 2.5 hr (incurring overpulls as large as 200,000 lb, with a 420,000-lb total string weight), the drill string finally became free. Because of the presence of a large iceberg approaching the location, the bit was then tripped to the surface for inspection. Although the bit was in very good condition, drilling resumed with a new C-4 bit and a new MBR.

At 2100 GMT on 27 September, iceberg number 107 of the leg passed within 0.5 nmi of the vessel, moving south at 1.2 kt. The first mate calculated the height of the iceberg using radar distance and sextant angle to be 135 m. The Captain then gave approval to reenter the hole, with the bit reentering the free-fall funnel cone at 2115 GMT. The bit was run into the hole to 166 mbsf without reaming, indicating that the top portion of the hole had now stabilized. The hole was washed and reamed from 166 to 231 mbsf, and then flushed with a high-viscosity mud. The bit was subsequently run back into the hole to 260 mbsf where coring was resumed. Rotary coring advanced in basalt from 260.0 to 302.7 mbsf, with increasing rates of penetration and excellent recovery. Within this interval, the average rate of penetration was 3.1 m/hr (with rates as high as 4.8 m/hr) with an average recovery of 85.9%. As coring advanced from 302.7 to 343.1 mbsf, the rate of penetration increased significantly and recovery dropped (44%-56%), with an extraordinarily high rate of penetration (7.2 m/hr) from 317.9 to 327.5 mbsf.

By 1200 GMT on 29 September, the winds had increased to 40 kt, with gusts to 50 kt from the north and 18-ft seas. The sea state was complex, with swells coming from the north and east. The vessel heave increased to 16-18 ft, with very short-period excursions. As a result, very rapid and confused ship motion developed, which caused the heave compensator to bottom out. Coring operations were stopped and the pipe pulled out of the hole to 144 m below sea level (mbsl) to wait for the storm to blow over.

The Storm

From the DMI weather forecast of 28 September, we expected gale force winds from the northeast, starting on the morning of 29 September and extending into the morning of 1 October. The maximum sustained winds were forecast to be 23 m/s (approximately 47 kt).

During the morning of 29 September, the winds increased gradually from the north to a sustained 42 kt, gusting to 50 kt by noon. The wind then began to slowly shift to the north-northeast and decreased to 20 kt by 1800 GMT. The winds then started to increase, with the direction holding steady from the north-northeast. When the new evening DMI forecast arrived (2130 GMT), the winds were revised upward in strength to 50-60 kt from the north-northeast to north for the next 48 hr, indicating rapid development into a full storm (Fig.1). By midnight (0200 GMT on 30 September),wind speed was back up to 40 kt and the seas had grown to 20 ft.

By 0600 GMT on 30 September, the wind speed was a constant 63-66 kt with gusts to 76 kt. It was now no longer possible to maintain the ship's position. The wind direction started to drive the vessel slowly westward toward the Greenland coast (approximately 30 nmi distant) and higher concentrations of icebergs. The Captain was awakened, called to the bridge, and apprised of the situation. Winds were now gusting to over 80 kt, and green water routinely came over the bow, threatening the functionality of the forward thruster motors, which are necessary to maintain the ship's heading into the wind.

Because of the very short wave periods (8 to10 s), the ship's stern was coming out of the water with every wave, causing the propellers to clear the water and overspeed to 200 rpm. The chief engineer set back the power limit to the main shafts, reducing the overspeeding of the propellers and the risk of overheating and bearing failure. The result of reducing power, was a loss of position, with the vessel moving slowly to the south. Even though the ship was buffeted by high winds, we could still maintain a northerly heading. East bias in dynamic positioning (DP) commands was necessary to prevent the vessel from being blown into ice flows west of site.

With the decision made to give ground to the storm, the vessel's motion then became less violent, but she moved aft at speeds of up to 4 kt. This attitude was made possible only by having the capability of applying lateral force to the forward end of the vessel via the bow thrusters. Lookouts were posted aft to ensure that no icebergs were overtaken.

By midmorning on 30 September, the winds had increased to a sustained 75-78 kt with gusts to 100 kt or greater (100 kt is the maximum indication possible with the shipboard system). This high wind speed (gusts of >70 kt) was sustained for over 26 hr. As waves broke over the bow, high-velocity sheets of spray raked the vessel. The weather stations were long blown away by this time, but it was estimated that the air temperature was about 3°C (sea temperature). The seas continued to build to 60-70 ft, with recorded pitch angles of up to 14° and rolls to 18°, extraordinary values in DP mode. The BHA remained hanging off on the 500-ton elevators.

At 1245 GMT on 30 September, the port outboard bridge window was blown in by a wave, knocking out both radar displays, denting in the bridge wall, and flooding the entire bridge. A group of Sedco and ODP drilling and technical personnel quickly transformed themselves into a crisis team and built a cover to the open window with plywood, 2" * 4" lumber, and tarp, and secured this improvised patch with screws and carriage bolts. During this emergency, many individuals risked their lives by exposing themselves to extremely high winds, very rough seas, and low temperatures as they stood outside the bridge to affect repairs. The efficiency with which the repairs were performed ensured that more water did not enter the bridge.

The large volume of seawater that entered the bridge migrated below decks via electric cable ways. Some forecastle deck compartments were flooded as seawater dripped from around overhead light fixtures. The water came within 1 vertical inch of flooding the DP computer electronics. If the DP computer had been shorted out, the only manner by which heading could have been maintained would have been to steam ahead into the seas with the main propellers. At a minimum, that would have increased the chances of more green water hitting the bridge windows and possibly taking out more glass. The lowest barometer reading of 979.0 mb was made at 1100 GMT on 30 September. After this, the barometer began to rise slowly and the winds slowly, almost imperceptibly, started to decrease.

During the storm, radio contact was lost with the Gadus Atlantica. A Danish Navy warship in the area and Greenland Command were apprised of the lost communication with the picket boat. At 2100 GMT that day, the vessel reestablished contact with the Gadus Atlantica, which had been steaming into the storm and was now well north of our location in good condition.

By 0400 GMT on 1 October, the winds had dropped to 57 kt with gusts to 65 kt, but waves remained over 60 ft in height. At this time, another wave hit the bridge deck and damaged the patched window, spraying the bridge with more seawater and shorting out the sole repaired radar display. The broken patch was quickly repaired.

At 0720 GMT, the forward thruster pod was lost as a result of water entering the motor housing. Several other thrusters were not operational because of overheating or flooding. Directional control of the vessel was then taken over by the mates on the bridge, supplemented by the remaining thrusters. Luckily, the reduced seas (40-50 ft high) and lowered wind speed made directional control considerably easier, and this method of maintaining heading worked well.

By 1500 GMT, the storm had abated to 37 kt, with seas down to 25 ft. The drillstring was then retrieved, and at 1815 GMT the vessel came about with the assistance of the remaining thrusters. After the hydrophones and thrusters were retracted, the vessel began the voyage to Halifax, Nova Scotia, for repairs, signaling an end to drilling operations on Leg 163. The Gadus Atlantica accompanied the vessel and provided surveillance of the transit path until one of the radar units was repaired.

163 Table of Contents

Publications Home

(ODP Home)