In the records of the losses of mobile drilling units there are many which took plac when they were under tow. This is a typical example, involving much which can go wrong with such an activity. Although it is 43 years since it happened there are still lessons to be learnt.
On April 15 1976 the mobile drilling unit Ocean Express sank in 167 feet (51 metres) of water in the Gulf of Mexico while under tow. Almost all the crew evacuated from the unit in two Whittaker capsules moments before it disappeared beneath the waves. Subsequently one of the capsules capsized and sank with the loss of 13 lives. The accident was investigated by the US Coast Guard and their report was published June 1 1978.
Vintage Whittaker Capsules innovatively used as hotel accommodation in Holland.
THE VESSELS INVOLVED.
The Ocean Express was owned by the Ocean Drilling and Exploration Company, ODECO, a substantial and experienced owner of offshore drilling units. It was a ‘mat supported unit’. This meant that the deck of the rig was supported by legs connected to a substantial hull which was lowered to the seabed, The legs of the Ocean Express were 312 feet (95 metres) long, the deck, or upper hull of the drilling unit was 166 feet (50.5 metres) long and 109 feet (33 metres) wide, and the mat, which would form a lower hull while the unit was in transit, and then provide a stable base when lowered to the seabed, was 210 feet (64 metres) long and 170 feet (52 metres) wide.
The “deck” of the rig contained the machinery and storage areas of the unit, as well as accommodation and social spaces for 56 men. At the aft end was the drilling derrick which could be moved forward and aft and to port and starboard, over what was known as the “slot”. The unit was equipped with a mass of emergency equipment which included three Whittaker capsules, two on the starboard side and one on the port side. Whittaker capsules were, and still are, more or less circular lifeboats whose principal advantage is the ease of launching. The makers also claim that they are easy to manoeuvre due to their shape. Inside there are seats around the periphery and seats around the centre so the majority of the people are seated facing inwards from the outside, and a small number face outwards from the centre. Each of the capsules on the Ocean Express had a capacity of 28 and once inside it was necessary for the passenger to do up seat belts for stability purposes.
The rig was provided with a single five ton anchor attached to 1000 feet of 2 ⅛” cable which could be lowered from a position on the deck by declutching the winch, removing a pin and releasing the brake,.
There were three tugs assigned to the task of towing the rig to its new location. The tugs were all about 100 feet (30.5 metres) long. The Gulf Explorer had been built in 1967 and had 3600 bhp available, the Gulf Knight was built in 1969 and had 2400 bhp, and the third tug, the Gulf Viking, also a 2400 bhp tug, had been built in 1966. A survey vessel, the Nicole Martin rescued survivors from the sea. Also briefly involved was the supply vessel M L Levy which was used to transport six offshore workers to the rig when it was under way, in readiness, one assumes, for the next job. Four of the six were to lose their lives when the survival capsule, in which they had evacuated from the rig, capsized.
Because of the later problems with the Gulf Viking’s towing equipment the report describes it in some detail. It was made up as follows: The pennant connecting the tow to the rig was about 50 feet (15 metres) long and had a diameter of 1¼”. This was connected to an 11” nylon towing spring, or snatch line 200 feet (61 metres) long, and this was connected to the tug’s tow wire which was 15/8” in diameter and was 1600 feet (488 metres) long.
The Gulf Explorer’s towing system was made up of a 1½” pennant wire, a 12” towing spring and a tow wire 2000 feet (610 metres) long of 2” diameter. The Gulf Knight was equipped with a 1¼” pennant, an 11” towing spring and this was connected to its 15/8” tow wire.
PREAMBLE
The Ocean Express was designed to operate on the level soft mud of which much of the seabed of the Gulf of Mexico is composed. When in its drilling position the mat was lowered to the seabed on the three tubular legs. When the mat was on the bottom, the hull could be elevated above the sea surface, and in this position drilling could be carried out.
The mat was of cellular construction, composed partly from tanks which were filled with water, and partly from tanks which remained buoyant. Since the mat contributed to the buoyancy when mated with the hull, as it was lowered towards the seabed, the stability of the unit would be reduced.
The rig move was carried out more or less under the control of an ODECO Barge Mover. Also involved in the management of the unit was a Marathon Oil company representative and the ODECO Toolpusher, who had been in charge of the rig when it was jacked up on the previous well and was to be in charge again when it reached its new location, which was only 33 miles away.
On the morning of April 14th 1976 the hull was lowered into the water and the mat recovered to a depth under the hull of 80 feet (24.5 metres). The most powerful tug, the Gulf Explorer was designated as lead tug. The rig was rectangular and the points where the towing gear was attached forward were small triangular areas on the port and starboard sides, approached through doors from the deck structures. The Gulf Viking and the Gulf Knight were attached to the towing point on the port bow and the Gulf Explorer to the towing point on the starboard bow, and in this configuration the 33 mile tow was accomplished.
There had been concerns about the freeboard of the unit, which should have been between seven and eight feet (2.5 metres), but the rig had a natural list to port which required counter-flooding, and the derrick was not positioned as far forward as was possible so ballasting forward had probably taken place, reducing the freeboard to as little and five and a half feet (less than two metres).
THE SEQUENCE OF EVENTS
April 14 1976.
2300. The tow is about one mile from the new location. The Gulf Knight is relocated from the starboard bow to the port quarter and the Gulf Explorer from the starboard bow to the starboard quarter. The Gulf Viking remains on the port bow. The rig is now positioned with the stern towards the location but is being held bow to the weather by the Gulf Viking, and in this position the mat is lowered until it is 148 feet (45 metres) below the hull. But during the lowering operation the weather has deteriorated and so the relocation is not completed. Instead the rig is held in position by the ships.
April 15 1976.
0600. The wind speed has increased and the seas are now about 10 to 12 feet (about three metres) in height. The supply vessel M. L .Levy arrives and transfers six Offshore Hammer employees by personnel basket.
0900. The Company Man requests a weather forecast from the Marathon Oil office in Rockport, and is told that they should expect southeasterly winds of up to 40 knots with 12-15 foot (4 metre) waves. He says that he passed this information to the Barge Mover and the ODECO Toolpusher, but they later deny having been told this.
Mid-morning. The weather has worsened further. Spray is blowing across the deck of the rig and seas are occasionally boarding. At this time the Barge Mover instructs the tugs on the aft corners to head forward to hold the rig on location. Some water is entering the hull through apertures in the deck, and uncomfortably for those in the accommodation, this results in leaks into the living quarters through the light fittings. Other spaces on the rig are also filling up, particularly the mud pits.
1510. If one accepts that water dripping out of the light fittings is more or less normal, the first sign that things are going seriously wrong is the failure of one of the engines of the Gulf Knight. The Barge Mover asks the ship if it wants to recover its tow wire and return to port, but the master opts to remain attached and to continue to hold the rig up to the weather. At this moment the tugs on the port and starboard quarters are steaming in the same direction as the rig is facing, the tow wires angled outwards and forward from the sides.
1530 estimated. Despite the optimism of the Gulf Knight’s master, he is unable to hold the tug head to wind with only one engine and it drops back until it becomes part of the tow rather than one of the ships doing the towing. The Gulf Viking is now taking the weight on the port bow, with the most powerful tug, the Gulf Explorer doing what it can to assist from the starboard quarter.
Late afternoon. The weather continues to get worse so that there is no question of the mat being put on the bottom. Tugs and tow are experiencing wave heights of up to 25 feet (7.5 metres) and wind speeds of up to 50 knots, far in excess of the relatively benign conditions which would be required to land the mat and elevate the rig.
1900. The port Whittaker Capsule is washed away, and the M.L.Levy which is, surprisingly, lying at anchor, is instructed to get under way and keep an eye on it.
1930. The tow line of the Gulf Viking parts, and although the Gulf Explorer is still attached, the rig wallows in the seaway while the deck crew attempt to re-attach the tow line. The break has occurred in the towing spring, and the three men on the tiny deck area find it impossible to recover the heavy nylon. The seas, which keep swamping the space, knock the men down and flood the Welder’s Shop, from which access to the area is gained. They eventually give up the unequal struggle and retreat. At this time some-one sounds the general alarm without instruction from the person in charge who is, depending on one’s viewpoint, either the Barge Mover, the ODECO Toolpusher or the Marathon Company Man.
2000 estimated. Shortly thereafter some of the pipes on the deck shift, causing the rig to list, and efforts to re-secure them are soon abandoned due the danger to the crew. The Barge Mover questions the need to sound the alarm, since in his view the rig is not in danger. The Marathon Company Man calls his supervisor ashore and asks for assistance.
2010. The Coast Guard Air Station at Corpus Christi receives a report from Marathon that the rig is sinking.
2018. The first Coast Guard helicopter is in the air and heading for the rig, but the Barge Mover is unaware that this action has been taken.
2030. The Barge Mover orders the two tugs to turn about and pull the rig astern. He also asks the ODECO Toolpusher to drop the anchor but this is not done. The rig continues to be at the mercy of the weather, the deck being under water for most of the time, the pipe on the Main Deck rolling from side to side and various compartments gradually filling up. Most of the crew have gathered on the upper deck wearing their lifejackets and are waiting for instructions.
2035. Communications are established between the rig and the helicopter. The Barge Mover says that the rig is not sinking, but that he would like most of the personnel to be evacuated. Flares are fired to guide the helicopter to the rig.
2110. The derrick shifts to starboard, increasing the starboard list. No-one investigates the reason for the derrick moving, but the Company Man is heard to say “Well, let’s all get into the capsules”, and immediately everyone but the Barge Mover prepares to board the two capsules on the starboard side. We remember that the one on the port side has been swept away.
2115. 14 men enter capsule No 1. All are wearing lifejackets. Most seat themselves close to the door through which they have entered, so the last few men have to cross over to the other side. All but two fasten their seatbelts. The capsule is lowered away to the water, and with some difficulty the Coxswain manages to release the fall, and motor away from the rig. The lookouts see the lights of a ship in the distance and the capsule heads for it. The engine appears to be overheating, but random operation of the various valves in the lifeboat are successful in reducing the temperature.
2118 estimated. 20 men enter Capsule No 3, 18 position themselves round the outer periphery and 2 are standing upright in the centre. The Derrickman assumed the position of Coxswain and the Driller and the Rig Mechanic take on the task of releasing the capsule from the rig. Initially the capsule sticks a few feet above the sea, but unaccountably resumes its descent and floats alongside in heavy seas, smashing against the hull a number of times. The Rig Mechanic attempts to release the fall, but is initially unsuccessful and suffers an injury to his right hand. But he returns to the task, at one point attempting to cut the fall with a small hatchet which is part of the capsule’s equipment. Finally the wire just seems to shake loose and release is achieved. The capsule motors away from the rig.
The Barge Mover is left on board, still believing he can save the rig. He gives the Gulf Explorer and the Gulf Knightinstructions to release their tow lines.
2120. The Coast Guard helicopter arrives at the casualty. The report contains the pilot’s description of the scene. He says that seas are breaking over the port bow and that the rig is listing about 25-30 degrees towards the starboard quarter. Seas are cascading over the deck from the port bow to the starboard quarter. The Barge Mover is standing on the helideck, requesting that he be taken off.
2130. The helicopter makes two unsuccessful attempts to recover the Barge Mover, and as it does so the list increases. At the third approach, with the helicopter’s personnel basket already lowered, the Barge Mover is recovered. Spray is entering the helicopter and within seconds of the rescue being completed the rig capsizes and sinks.
2140. Capsule No 3 is now some distance from the rig but the engine is overheating and the fumes and smell of diesel are causing headaches and seasickness amongst the crew members.
2145. Capsule No 1 is alongside the survey ship Nicole Martin and secured by two lines.
2200. All the personnel from Capsule No 1 are recovered to the Nicole Martin without injury, despite the extreme weather which is causing the capsule to ride up and down about 10 feet (3 metres) against the hull of the survey ship.
Probably at the same time, (although no-one actually had an opinion about this), Capsule No 3 is alongside the Gulf Viking and one of those who has designated himself as being in charge requests that it be allowed to drift astern so that the tug can tow it into calmer waters. The report is extremely detailed about the possible course of events at this time, and it seems that the survivors all disagreed with one another as to what happened. But at best it appears that when the capsule is about 20 feet (6 metres) astern of the tug, with a line still attached, it flips over at the top of a wave and floats upside down. Most of the people inside tumble about having removed their seatbelts. Survivor testimony indicates water is coming in through the top hatch – now at the bottom – because it has been left open. Thereafter seven crew members escape through the side hatches of the capsule and are rescued by the tugs on the location.
A late participant in this drama was the aircraft carrier the USS Lexington, which arrived on the location at about 0230 on April 16, in time to assist with the recovery of the capsules. And over several hours, with the involvement of some navy divers and the supply vessel M L Levy, attempts to recover Capsule No 3 were made. Finally at about 0600 the capsule was hoisted a board the aircraft carrier using a cargo net.
THE INVESTIGATION
Subsequent to the sinking, on April 25 an underwater survey of the Ocean Express was undertaken and no damage was reported. The depth of the sea at the location of the casualty was 155 feet (47 metres) and subsequent to the sinking one corner of the mat was breaking the surface, and constituted a hazard to navigation until February 1977 when the mat and approximately 100 feet (30 metres) of each leg was salvaged.
The investigators enumerated the detail of the activities of the towing vessels in the time immediately before the event, principally to determine whether there were any likely failures of the towing systems or the engines. There were none. The tug Captains also testified that they had found the Barge Mover’s instructions appropriate for the activities being carried out.
There is some detail about the manner in which the 11” towing spring of the Gulf Viking had been made up, how many times it had been used, at what times it had been inspected, and how had it been stored. There seemed to be nothing wrong with any aspects of the supply, use or storage of this line. However neither the master or mate of the Gulf Vikingwere aware of the breaking strain of any of the components of the towing system, and hence they were unaware of which part was the weakest. In general they judged that the weight on the tow was not excessive if the stretcher did not rise out of the water, and felt that the use of excessive power would be the reason for any breakage.
After the failure of one of the Gulf Knight’s engines its Captain informed the company home office of the problem and the tugs exchanged information in French. The report states that the tugs frequently communicated in French. The Gulf Knight’s engineer was asked to produce the engine room log for the vessel. He had been in charge of the machinery on the tug since June 1975. The investigation concentrated on the clutch failure of the starboard engine, and it was found from the logs, that the starboard gearbox had required fairly constant topping up with oil for the previous eight months. As is the way with these investigations those being interrogated are often embarrassed by their lack of knowledge of their own systems, and this was the case with the Port Engineer for the Gulf Mississippi Marine Corporation, who was unsure whether the Gulf Knight was provided with the correct maintenance manuals.
There is a whole section in the report on flooding and stability. Firstly the investigation dealt with the unexplained list to port, which had been evident for four months, probably the life of the rig, since it had only entered service at the end of the previous year, and about which a variety of investigations had been carried out, but without any resolution. The Barge Mover attributed the list to an error in the light ship calculations but the report considered this to be unlikely, since an inclining experiment had been only recently carried out, and considered it more likely that the list could be explained by undetected liquids or consumables. Regardless of its origins, this list required correction and therefore addition liquids were taken aboard, thereby reducing the freeboard. An additional cause of the reduced freeboard was the fact that the derrick was left in the aft position, apparently custom and practice for short moves. This would have resulted in the need to load water into the forward ballast tanks, thereby causing another reduction in freeboard.
Also discussed is the decision taken by the Barge Mover to keep the mat in the lowered position. It may be remembered that most of the move was carried out with it at 80 feet (24.5 metres) below the hull, and that as the new location was approached it was further lowered to 148 feet (45 metres). This decision had an adverse effect on the seaworthiness of the rig.
The report goes on to state that the boarding seas as a result of the reduced freeboard, the loose drill collars and the additional water underdeck, as well as the lowered position of the mat, caused a sufficient reduction in the righting curve to cause the rig to capsize.
In addition to all of the above, the investigators felt that it was likely that at quite moderate angles of heel that the mat would have touched bottom, and therefore would have contributed to the capsize due to ‘tripping action’. And this does not seem unlikely considering the fact that with the hull of the rig upside down on the seabed, the mat was visible on the surface.
As usual, there were deficiencies in the manner in which emergency drills and training were carried out. The Ocean Express had only been in service for a few months and so that would be the total length of service of all personnel on the rig. In addition emergency drills had been intermittent and training on the use of the Whittaker capsules limited. The Rig Mechanic is specifically referenced in the investigation possibly because he was assigned to be in charge of Capsule No 1. No-one, the report says, was assigned to be in charge of Capsule No 2. And the Rig Mechanic, although he was a bit hazy about the numbering of the craft, was aware of which one he was supposed to board. However he was not aware that he was in charge, and had had no training in the operation of the craft.
As part of the sales package of the Whittaker capsules the vendors provided training for the crews of the rig, and as a consequence personnel from that company were on board on January 13 and 14. The training package involved the showing of a training film and the lowering to the water and operation of the capsules. On the first day 29 crew members received the full training package, but on the second day the other crew, which was the one on board at the time of the casualty, was not instructed in the operation of the craft, since they were not launched due to fog, rain and high winds. In addition only nine crew members participated. None of the training material covered towing of the capsules, or the disembarkation onto other vessels.
In addition to the above, the requirements for the frequency of drills in accordance with the Station Bill were not followed, new personnel were not given any instruction and none of the capsules were lowered to the water during drills.
The investigation reviewed the regulatory requirements for self elevating units, which appeared at the very least to be limited, and there was a detailed review of the rig’s “Operating Booklet”. This document was provided as a requirement of the ABS rules and within it there should have been instructions for “Operating the unit including adverse weather, changing mode of operation, any inherent limitations of operation, etc”. The report says that it became apparent during the interviews of ABS personnel that the classification society did not actually review the document to make sure that it conformed to its own rules, but rather they relied on the owner or builder to ensure that the contents were appropriate. Neither did the Coast Guard fully review the document, limiting their involvement to an examination of the intact stability information. Hence one might have been misled into thinking that the booklet was suitable for the operation of the rig, since it contained stamps from both organisations.
In fact the booklet did not contain information about how to operate the craft in adverse weather, or what the effect on stability of the different positions of the mat might have been.
The report contains several pages of investigation into the weather forecasts provided to the rig, and the capabilities of those receiving them. And this information can probably be summarised by the statement made by one expert who felt that observations both onshore and offshore should be improved, and that the national weather forecasting service should in addition to the existing meteorologists have one specifically dealing with marine forecasts. Indeed the report contrasts the differing services available from the National Weather service for aircraft, even private pilots, and those made available for mariners. The former is a service which allows individuals to call a special number to get detailed weather information, while the mariner is more or less left to his own devices, unless a private weather service is subscribed to. However the expert witness stated that small scale anomalies of the type which overcame the Ocean Express are difficult or possibly impossible to predict.
The report goes on to detail the actions of the Captains and crew members of the tugs, some of whom risked their lives by standing on the tyre protection outside the bulwarks of the vessels, and heaving the people from the water aboard. And also helicopter pilot who, from his testimony had been operating on the edge of what was possible, hovering in high winds, with no proper points of reference.
When summing up the content of the investigation the board stated the following:
The board is apprehensive that despite a careful discourse on the specifics of the Ocean Express casualty, that similar casualties will continue to occur. Meaningful corrective action involves recognition of certain limiting inherent characteristics of self-elevating drilling units and implementing the necessary procedures to keep self-elevating units out of trouble in a class basis.
The report also suggested that the current oversight, regulation and organisation of the movement of jack-ups was insufficient to effectively reduce their vulnerability in adverse weather and as a consequence it was necessary to require specifically approved towing plan for each move.
There was then an almost philosophical discussion on leadership, what it constituted and who should be in charge on jack-ups. And it was evident that a number of people on the rig thought they were in charge, or could be, and that this might have led to some confusion. In the end the board though that the Toolpusher should be the person in charge and that the Barge Mover should be an advisor. The Company Man, who almost always thinks he should be in charge, did not get a mention. Supporting this view were the shortcomings evidenced by the Barge Mover. Although not supported in many ways by the Operations Booklet, he was found to have failed to take into account the state of the weather, and what was developing. He should have known more about the internal operation of the rig, including the valving between the tanks and the means by which the derrick was secured in position, and even though there was no guidance about how to position the mat, it was inadvisable of him to lower the mat rather than raising it as the weather deteriorated. It was evident, from his view that the rig was not in danger up to a few minutes before it sank, that he did not really have a handle on what was going on, and it was thought that without action on the part of the Toolpusher and the Company Man there might have been more deaths. The Barge Mover was also taken to task on his various judgements about the capabilities and the failings of the tugs. He also allowed the Offshore Hammer employees to join which was specifically against the industry policy stated in the Manual of Safe Practices in Offshore Operations, which says that only those required for the moving operation should be on board.
There are threads within the report about the testing, training and operation of the Whittaker Capsules, obviously because it might have been as a result of the capsize of Capsule No 3 that 13 people lost their lives. And the board approached this failing in two ways. It suggested that it was not evident if one was in an enclosed lifeboat, what became known as a TEMPSC (Totally Enclosed Motor Propelled Survival Craft), how it should be operated and how one should evacuate from it if that be came necessary. It also states that Whittaker had claimed, or inferred, that the capsules were impossible to capsize.
To summarise, the board also found much wrong with the manner in which the rig had been operated, both in general and on that particular occasion, aspects singled out for mention being the difficulties of making the tow fast on the tiny triangular decks. There was also considerable discussion as to what constituted a “field move” and what might constitute a “short move”, which would be amusing but for the tragedy which resulted from the confusion created by such distinctions. The board had something to say about the qualifications of the tug’s personnel, suggesting that offshore tugs should be subject to the same regulations as other vessels of a similar type, and that the chosen language to be used at such time should be English – the Louisiana tug crews tended to speak French.
There were also extensive recommendations about what should be contained in the Operations Booklet, all intended to ensure that any move would be appropriately planned and that adequate checks should be carried out on the equipment installed on the rigs, and how the deck load should be dealt with and secured. It was also considered advisable that the Toolpusher should be trained, experienced and licenced, by regulation, and it was also suggested that Barge Movers should be licenced and that the exemption from marine licencing for offshore tug personnel should be removed.
And finally it was determined that ABS and the US Coast Guard review the whole business of intact and damage stability for self-elevating units.
COMMENT
In hindsight it appears that the findings of the court of enquiry were extraordinarily predictive, but despite them the tragedy set a pattern which was to be repeated on many occasions in subsequent years. The only lesson learnt has been that these objects, which are normally elevated on stilts above the waves, become unacceptably vulnerable when afloat, and that therefore when things go wrong the best thing to do is to call for help.
For those slightly confused by the small size of the tow wires and the large size of the towing spring, for non mariners, for some reason sizes of rope are expressed as a circumference and sizes of wire by diameter. But either way the wires, and if it comes to that the towing springs, do seem to be of very small dimensions, which might be commensurate with the bollard pull of the tugs, (not mentioned in the report), but might be strained by the snatching which could result if the rig was moving in rough seas. Also nylon stretchers have always proved themselves vulnerable to destruction, and later in the evolution of the towage of offshore objects it became more common to use lengths of chain to take up the shock loading rather than nylon.
The investigation was very thorough and extensive interviews of all those involved were carried out. This might be because there was a serious loss of life, and one cannot help thinking that if everyone had been saved the investigation would have been less thorough. But actually it should not matter whether lives had been lost or not, the casualty needed to be thoroughly investigated and conclusions and recommendations made. Whether anything is done about the recommendations is another question.
The Coast Guard, while they have massive resources and an effective operating structure, seem to have been keen to exempt aspects of the offshore industry from what might be called ordinary marine regulations, and the questions must remain. Why did they exempt offshore tugs from aspects of the US marine regulations and why did they exempt the Whittaker capsules from other regulations?