Craig Matthews, cited and pictured in the article, is my son-in-law's father. He's told this story a few times in my presence and I've always got the chills. What this article doesn't mention is that when he grabbed the floating cable, the size of a man's arm, with the grappling hook, the two vessels were both riding up-and-down on monster waves. So first, they had to synch both up to even make the grab possible. To hear him tell it, it was a totally hair-raising experience. His peers now know him as "The guy who tied THAT KNOT on THAT DAY." It may be the most famous "Bowline" knot ever after that write-up.
"Between 5:34 a.m. and 11:29 a.m., according to a later computer analysis by Rolls-Royce, the Aiviq’s “wire tensile strength overload” alarm went off 38 times. It was set to trigger at 300 tons. The alarm, a piercing ring, would not stop until Newill acknowledged it on the computer screen. New to Alaska and new to a ship that was new to the world, Newill later claimed that the alarm never went off. Coast Guard investigators concluded that he mistook the tension alarm for another alarm that was known to be acting up."
Dialog box on screen saying which alarm might have been an idea perhaps. Software was obviously logging all the events.
Nothing in the article suggests this alarm is based in software. Couldn't it just as easily (in fact rather more easily) been a strain gauge hooked up to an amp and comparator with a buzzer?
…would not stop until Newill acknowledged it on the computer screen…
Sounds like software to me. I suppose you could put a computer controlled relay into your physical system, but the software would still have to know which alarm it was disabling.
...and the Rolls Royce technical people must have had a log of some kind to know that the alarm had sounded 38 times. I suppose it could be a tachograph type mechanical log...
Extraordinary story. What I always found strange was how super rich corporations like Shell will skimp in making purchases of the required safety mechanisms, try to avoid taxes etc. and will ultimately end up with disasters such as this one, which could have been avoided if the tug had been stronger or better equipped, and the shackles had been new and strong.
The shackle gets a lot of ink in the media, and it did fail. The questions about who inspected it and how seem a bit misplaced given that it was rated at 120 tons and the tow line alarm registered over 300 tons more than 30 times, so missing provenance or not, it seems like the shackle was performed beyond its design limits and beyond what the engineers required. They were just wrong.
The towline itself was only rated to 85 tons, the towline manufacturer did well.
Typically, shackles of this sort have a safety factor of 5, meaning that if the maximum working load is 120 tons, the minimum breaking load should be >= 600 tons. Strictly, once the maximum working load has been exceeded, the shackle should be considered compromised. I don't have experience with any shackle on that scale, but my feeling is that you ought to be able to expect a good shackle to withstand 30 pulls to half of its minimum breaking load.
It seems like a kind of tragedy of the commons. There are many people involved, and each one can reap some personal reward by cutting corners just a little bit ("I should get a raise because I saved the company X dollars in Q3 by reusing existing assets!"), but if enough people do that, and you get a little bit of bad luck, then you get a failure cascade that threatens far more money than anybody saved.
