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Precis File
SHIP NAME: Texaco Oklahoma KEY: NUM. ENTRIES: 5
source USCG
type D
volume
material
dead 31
link http://www.uscg.mil/hq/g-m/moa/boards/texoklahoma.pdf

American flag ship was very fully loaded with black products, Port Arthur to Boston. Broke in two 120 miles NE of Hatteras in way of No 5 tanks, just aft of the forward hous in whole gale, winds 60 to 65 kts, 30 to 40 ft seas, 31 of 44 onboard died including all the deck officers in forward house.

The USCG somewhat simplistic calculations showed that the fully loaded ship would have been subjected to about 81 pct of the steel's yield stress in the design wave, in part because the 1966 Loadline regulations had allowed a 2130 ton increase in deadweight. The USCG comes up with a max stress figure of 11.6 tons/in2, compared with a yield stress of 14.3 tons/in 2. Moreover, the reports point out that the Loadline regulations allow summer deadweight off Cape Hatteras in the winter despite the very stormy conditions. The report concludes this was done with out any real study of the wave conditions off Hatteras.

This was all based on the as-built scantlings. The USCG found that many of the Oklahoma's tank had not been inspected in the last two years including 5P. They did an inspections of a number of sister ships and found many tanks with 25 to 30 pct wastage, just within legal limits. One near sister's deck had buckled in calm water. Yet the report belittles these findings, claiming that the wastage was almost certainly within legal limits and not an important contributary factor. Nonetheless one of the recommendations was for slightly tighter tank inspections requirements.

This ship had a 3 by 10 tank arrangement with the ballast tanks being rotated to even out the corrosion. The actual failure was in way of the No 5's, about 50 feet forward of the midships max stress point.

The bow section almost immediately assumed a bow up position. All 13 men forward were lost. The bow section drifted back to the stern and clobbered a lifeboat, and sank sometime later. The stern section floated until 0600 the next day. During that period, the men aft tried to tranmit a distress signal on a hand-cranked transmitter. But the RO had been forward, it was fairly complicated process, and no signals were ever received. Heavy seas carried away the other lifeboat. When the stern section started to sink, they attempted to abandon ship in liferafts, but only 13 of the 31 men aft survived.


source NTSB
type A
volume
material
dead 31
link http://www.uscg.mil/hq/g-m/moa/boards/texoklahoma.pdf

The NTSB determines that the probable cause of the Texaco Oklahoma hull fracture was the high stresses produced by heavy seas and other forces on the relatively lightly constructed, fully loaded ship. The design, maintenance, and operating standards inherently contained risk levels which were excessive for vessels of this type transiting the seas off Cape Hatteras in winter storms.

    The following are considered to be contributing causal factors:
  1. The use of a section modulus which results in a relative stress near the upper end of the acceptable limit, and therefore, a relatively high risk level.
  2. The increase in the loadline of the Texaco Oklahoma in 1967 without changing the section modulus, therefy increasing the loaded sagging stresses and the wave induced loads, with the consequent increase in risk level.
  3. The year round designation of seas off Cape Hatteras as a summer zone for loadline purposes without knowledge of measured sea conditions in the winter storms that frequent that area.
  4. The low probability, with the techniques used during annual dry dock and biennial inspections, of detecting all cracks and assuring that steel wastage for all portions of the tank interiors has not exceeded permissable limits.


source OSIR
type D
volume 32143T
material fuel oil
dead
link

Location Northwest Atlantic ocean Says data is 19710326.


source HOOKE
type D
volume
material fuel oil
dead 31
link

31 crew members lost their lives as a result of the American steam tanker Texaco Oklahoma breaking in two aft of the amidships house in heavy seas and high winds of the coast of North Carolina in lat 36.00N, 73.43W on March 27, 1971. The Teaco Oklahoma had been en route from Port Arthur to Boston with a cargo of No 6 fuel oil when she ran into very severe weather with gusts of 80 mph. She suddenly broke apart at 3.30 PM, apparently through the impact of one very large wave. According to one survivor "the forward section broke free and came back against the stern section ripping out some lifeboats".


source CTX
type C
volume 220000B
material
dead 31
link

The USCG says 220,000 bbl cargo which is 35,000 m3.

The water temp was a surprisingly high 74F, Air temp 55 to 65F. Brittle fracture can be ruled out.

The CTX believes that in this case the emphasis on the change in the loadline regulations is misplaced. As long as the Trim and Stability Booklet did not change, the stress limits along the hull were the same before and after the change. It is true that the new Loadline Regs may have made it easier to load the ship up to the stress limits.

No mention of tank coating, and ballast was being rotated to even out wastage. It is pretty clear that all the tanks were uncoated. 5P and 5S were empty on this trip, so it is very likely that these two tanks were part of the ballast tank rotation. The USCG's stress estimation does not seem to have worried about the shear stress in way of 5's.

The USCG estimates as-built stresses could easily have been 80 pct of yield. The USCG also finds sister ships 25 to 30 pct wasted and in one case (Texaco Wisconsin) 40 pct. The USCG figures this ship had similar numbers although some tanks had not been inspected for more than 2 years. And then says corrosion was not a factor.

The NTSB in its carefully worded conclusion is slightly more forthcoming.

The CTX thinks this is patent nonsense. The USCG is in a bind. Since this was an American flag ship, at least in 1971, the USCG was responsible for inspecting the ships. If the ship was lost because of lousy steel condition, then part of the blame lies with the Coast Guard. At this point the USCG is investigating itself.

The CTX is quite confident in making steel wastage the primary cause of this hull failure. The wastage was combined with a marginal as-built stress pattern. The failure probably started at some crack which very quikcly propagated through the weakened structure.

In the end the loss of the Texaco Oklahoma changed nothing.