Argo Merchant: ‘A study in casual navigational procedures’

The previous series of articles focused on collisions, the navigation rules and when known, the courts’ interpretations of those rules. The next several will shift gears and focus on strandings. The approach will be the same — the situation leading to the event, action taken (or not), the result and its aftermath.

It would seem that in many cases of both strandings and collisions, they are often not related as much to inadequate equipment or lack of information, but that what was available was not used to its full capability. 

Variation increasing – depth decreasing

Some years ago an ecological tragedy was barely averted when a tanker carrying 7.7 million gallons of No. 6 heavy fuel oil enroute from Venezuela to Salem, Mass., grounded and subsequently broke up in the waters of Nantucket Shoals. It was only by a fortuitous smile of nature or, as the subsequent investigation exclaimed, “by the intervention of the Almighty,†that a disaster was averted for south-facing Nantucket and eastern Cape Cod beaches and for sea life for years to come. Recent events underscore the environmental catastrophes that lurk, whether the pollutant comes from a fractured seabed or fractured hull. 

The flag state’s post-accident investigation report recorded that the vessel’s navigational equipment “if it had been functioning, was adequate.†It included 3- and 10-cm radars, an RDF (including a sensing antenna), a recording fathometer, a master gyro with three repeaters (with their limitations as noted below) and a magnetic compass. A course recorder was installed but was not functioning, and there was no Loran aboard. Charts were six years outdated to the degree that a navigation mark planned to be used as a waypoint was nonexistent, as it had been removed. 

The helmsman was blessed with one of the two functioning gyro repeaters on the bridge; the one other functioning repeater was mounted on the pilothouse bulkhead in such a manner as to make it unusable for bearings aft of either beam. A third on the flying bridge was (and had been for over a year) inoperative and there were none on the bridge wings. This made the taking of navigational bearings or azimuths for gyro error checks somewhat more than a challenge.

The master stated an intention to take Nantucket Lightship about 3.5 miles abeam to port, but the track laid out on the chart was directly to the lightship, 040 T from his vessel’s noon position off Cape Hatteras the day before. As part of the investigation, examiners later laid down the most likely track made good by the vessel, given leeway, the gradually increasing magnetic variation and information from the depth recorder.

During the period of transit from Hatteras to the point of stranding, the magnetic variation increased from 8.5 W to 15.5 W. The investigation noted that although the deck log recorded a gradual decrease in the mag/gyro difference instead of an increase, this anomaly apparently drew no attention until the chief mate, a few hours before the stranding, expressed his anxiety to the master over failure to take the variation change into account. Additionally, during the initial phase of the Hatteras-Georges Bank leg, a 4-degree course change to port had been made to compensate for weather-induced leeway. Despite the eventual backing of the winds from the port bow to nearly astern, the course adjustment was not eased off.

Some 12 hours before the stranding and at the end of the first dog watch, unusual yaw led the mate to check the helm gyro repeater — discovering that the gyro had become erratic with rapid oscillations +/- 7 degrees. There was some disagreement as to whether the problem was with the master gyro or isolated to the helm repeater; in any event, the steering was shifted to magnetic. From then on, there was inadequate adjustment of the magnetic course steered to account for the increasing variation.

The watch gave testimony that “(f)rom time to time the RDF was switched on,†the signal reportedly being heard “dead ahead.†The conclusion of the investigation was that picking up the signal of the Nantucket Lightship directly ahead “was a physical impossibility.†

Relative to the vessel’s course, the lightship (and its RDF) progressed from sharp on the starboard bow to the starboard quarter. At no time in the entire transit from Hatteras to Nantucket was the signal (relative to the vessel’s head) either dead ahead or dead astern; it would have passed gradually down the starboard side. (To be complete, it should be noted that the use (and understanding) of the sensing antenna was raised in the report.)

Between 0330 and 0400, when the lightship was expected to be 3.5 miles on the port beam, it was approximately 15 miles to starboard and had not been detected by radar. At that time, the vessel was crossing into 20 fathoms instead of the charted 35 that the fathometer would have been showing if in the lightship’s vicinity. 

Both the watch officer and master admitted that they observed that “the depth of water reduced to between 15 and 20 fathoms.†Examination of the chart fails to show any depths less than 35 fathoms along the intended track. Examining the reconstructed track shows soundings below 30 fathoms about 0300, below 20 about 0400, below 10 about 0515. 

At 0600 on Dec. 15, 1976, the Liberian-flagged 644-foot tanker Argo Merchant grounded off Nantucket on Middle Rip Shoal at 41° 2’ N/69° 27’ W. Six days later she broke up, releasing her oil cargo. The fortunes of weather took the spill out to sea, sparing the island beaches a catastrophic environmental and economic loss. The crew was taken off safely and there was no loss of life.

In the publisher’s note to the second edition of “Strandings and Their Causes†(The Nautical Institute) C.J. Parker BSc FNI observed, “with respect to strandings, it is salutary that few of the incidents occurred because those on board had no means of determining their position.â€

The known gyro error was 1 to 2 degrees, but although the situation with the gyro repeaters noted earlier made determination of gyro error using azimuths difficult, and obviously important, this had no effect on decisions made in the 12 hours between gyro failure and the stranding. Available were a magnetic compass with zero deviation on the relevant courses, variation data on the chart, a functioning and accurate fathometer and perhaps the best instrument when uncertain — the anchor. The final report of the Marine Board of Investigation, published by the flag state, concludes in part that “(t)he history of the trip from Cape Hatteras to the point of stranding was a study in casual navigational procedures.â€

About the Author:

Following graduation from the U.S. Naval Academy, Jim Austin served aboard both a destroyer and cruiser with duties that included navigator, assistant CIC (combat information center) officer and air intercept controller. He subsequently worked on the submarine launched ballistic missile program for the General Electric Co.’s Ordnance Division. He holds a U.S. Coast Guard master’s license and writes frequently on ship collisions as seen through the twin lenses of the navigation rules and maritime law. He’s a retired physician living in Burlington, Vt.

By Professional Mariner Staff