Update 11th February
This article has now been replaced by an updated and more accurate version that also includes conclusions, however we are leaving this one up for a month or so because of the valuable comments that inform the new article.
I started this article evaluating the Backtow™ feature of the TeamO lifejackets, but quickly realized that first I needed to figure out the tether tension a crew member who falls overboard will experience while being dragged, before the remaining crew can slow the boat.
This was doubly worth my time because many of the chapters in this Crew Overboard Prevention and Recovery Online Book will benefit from a better and more granular understanding of these loads, rather than the simple single-number estimate that I used when writing them.
Also, despite googling like a fiend, I was not able to find any studies, or even sensible guesses about what tether loads will be when being dragged. Seems the industry and safety regulators have their heads firmly up…err…in the sand about the whole issue.
Scary when you consider there are thousands of sailors out there clipping to sidedeck jacklines, or hard points close to the edge of the deck, with standard 2m (6 foot) tethers, on the assumption that if they fall in their buddies will haul them out and all will be well.
And, of course, the key question about TeamO jackets, which everyone seems to be ignoring, is will the COB be in good enough shape after hitting the water to activate Backtow?
So let’s dig in, and after that I will finish my thoughts on Backtow.
Brace yourself. I will share a lot of detail so that the technically oriented readers, particularly you engineers, can correct any errors I have made in either my assumptions or calculations. Think of this as a working paper exploring a complex subject.
So if you don’t feel like reading all of this, it’s fine to skim, focusing on the text in coloured boxes, tables, and graphs, and then read the example scenarios where I really get to the meat of it. You also don’t need to worry about the footnotes, unless interested, which make up a lot of the word count.