Most of the time, damages to marine vessels and structures are straight forward: there’s a collision, allision, or sinking due to mechanical failure, procedural failure, negligence, or an unfortunate concurrence of events. The involved vessels/structures are damaged, the damages are tallied up, and a direct line between the cause and the effect can be drawn. These tasks are staples of a marine surveyor’s skillset; find the cause, list the scope of damage, and provide a list of recommended repairs.
Then there are those cases where the link between the cause and the effect are a bit more disconnected. This study will go over, in a generalized fashion, such a case.
The background behind the case is thus:
a barge with a permanently mounted crane was performing dredging work above buried infrastructure in protected shallow water. Work was contracted for single shift; the shift was ending for the day and a rainstorm was predicted for the evening. Predictions from different sources conflicted as to the intensity of the storm – some said light to moderate, others heavy with gusty winds. The crew secured the barge for a rainstorm with moderate winds, presumably lashing the crane boom. Late in the evening, an observer on land noted the lights of the barge were not to be seen and notified the owner. In the morning, after the storm passed, the barge was found to have capsized to starboard and foundered.
An experienced marine surveyor was assigned by the hull insurer to look after the interests of the insurer and determine cause; based on sonar and diver images, it was expected the barge and crane would be a total loss. After an operation to upright the capsized barge indicated a direct lift of the barge was impossible, alternate plans to section the barge for salvage were created. The marine surveyor, realizing the complexity of this recovery were beyond his experience, recommended this Professional Engineer to the insured.
The insured tasked this Professional Engineer with the following:
- Review the recovery plans to ensure the barge was recovered as intact as possible and limit potential collateral damage.
- Examine the barge for material defects which could have caused the barge to founder
- Determine the root cause of the foundering
The first proposal for sectioning the barge was to use a guillotine – drop a large plate blade down on the barge; this Professional Engineer objected to this approach given the infrastructure under the barge’s position. The adopted plan used divers with cutting torches to section the barge in two halves – safer, but more time consuming. Once the two sections of the barge were retrieved, examinations of the hull could be done. Information known about the barge indicated steel renewal had been done at the bow years earlier; there was a concern that the repairs were unsatisfactory or incomplete. The hull examination did not reveal this concern as a cause for the foundering; the barge was externally intact on the bows. Ultrasonic gauging of the steel indicated general wastage and some small breaches in the hull were found; these breaches were too small to have sunk the barge in a few hours and could arguably been an artifact of the uprighting operation.
The marine surveyor and this Professional Engineer did find a submersible pump in a compartment on starboard side. Examination within the compartment found the hatch for the flush deck access lodged in deck transverses above the location of the submersible pump. The retrieval line and power cord for the pump ran through the access onto the deck. This compartment was identified as the most likely point for water to flood into the barge. But how? The barge had ample freeboard for unrestricted operation in a protected location.
This Professional Engineer then had to determine what mechanism would spill water into the compartment. Weather reports from nearby stations were collected for the date of incident; plans and images were reviewed of the crane and barge. The mooring arrangement was reviewed. The barge was not fitted with a boom rest; the boom could not depress below a plane parallel to the height of the crane foundation. The boom was a lattice boom. At the presumed time of loss, the winds were coming from the port forward quarter of the barge with sustained speed of 24 knots with gusts to 35 knots. Swell was about 2-3 feet. No stability documents were available to the investigation; basic stability was calculated based on the observed hull form of the barge.
Lattice booms are open; there is more gap than steel. However, at narrow angles of exposure to wind, an interference effect between the lattice tubes occurs and the structure appears more like a semi-permeable sheet against the wind. This interference effect over the length of the boom plus the windage of the crane cab itself was calculated to be enough to heel the barge past the starboard deck edge. The access to the uncovered compartment was only 2 feet away from the deck edge; it would have been easy for the swell that evening to spill over into the open access. Progressive flooding would have occurred; the stability calculations indicated with the list imposed by the wind and the water in the compartment, the barge would have capsized to starboard and sank.
The root cause of this foundering was unanticipated strong winds combined with a compartment access which could not be secured closed due to pump cables. Contributing to the foundering was a general deterioration of the barge including possible access hatches with insufficient sealing to prevent downflooding.
About the Author
Steven M. Lindholm, P.E., P.M.P. is an engineering manager and consulting engineer with our Oakland Office. As an approved Third Party Organization (TPO), EDT can audit the Safety Management System of towing vessel operators, issue Towing vessel Safety Management System (TSMS) certificates, survey towing vessels, and issue survey reports.
Beyond his capacity as the TPO lead surveyor, Mr. Lindholm consults on inspection, evaluation, and design analysis of ship construction; stability; propulsion and auxiliaries condition assessment; ballast water treatment systems; vibrational analyses; and ship motion. He interprets and applies international (International Maritime Organization (IMO), class society, and flag state), United States Coast Guard (USCG/CFR), and regional regulations/guidelines to maritime casualties. Mr. Lindholm explores root cause investigation and analysis of mechanical damage to equipment, components, and materials, including fracture analysis and failure analysis, and prepares repair and replace cost estimates for marine, industrial, commercial, and residential systems. You may contact Steve for your forensic engineering needs at firstname.lastname@example.org or (925)674-8010.