Posted by: towmasters | May 16, 2010

Perception, Reality & Mooring Lines: The Not-So-Ordinary Practice Of Good Seamanship

Perception and reality: they’re not necessarily the same thing. Perception’s in the eye, and mind, of the beholder. Reality is whatever it is, and it’s always non-negotiable. Here’s a “scenario.”

Scenario: a light barge is moored at a dock with significant overhang of the bow and, although weather conditions at the time are benign, winds gusting to 40-plus knots are forecast for later. The predicted direction for these winds is perpendicular to and off the dock. The barge has orders and is expecting to move to another dock for loading at some point, but no specific time has been decided upon by the terminal yet. The barge might be at its current location when the winds come, it might be at the loading berth, or somewhere in between. No one can say. For that matter, the forecast may or may not turn out to be correct. But in the absence of convincing evidence to the contrary it should be heeded.

Perception: The tankerman says “we’ve got seven lines out, we’re fine.”

Ah, yeah…..here we go again. The total number of lines put out is basically meaningless. Far more important is how and where they’re set, their size and condition, and whether or not they’ll actually do what they’re intended to do. We’re actually not “fine” at all, just riding on luck. Again.

Reality: The bow line, which is on the windward side, has been tightened up with a capstan to the point where it is essentially the only load-bearing line for the entire forward half of the barge. Should it part the next line(s) to take a strain (one or both of the bow springs) will be heavily shock-loaded. Because of the over-tightened bow line they both have a fair amount of slack in them, so you can expect that the heavy shock load they receive when they come tight may well cause them to part immediately too. If they go the bow will have fallen off significantly and the advantage of leverage tilts decisively to the off-the-dock winds. The whole barge will likely just peel away from the dock like a zipper as all the other lines let go: Pop, Pop, Pop, Pop, Pop!!! Then the real fun starts…..breakaway barge(s). If you’re really lucky, the stern line might hold for a little while once all the others have parted and the barge is free to point downwind, presenting a minimal surface area for the wind to work against.

To properly secure any vessel to a dock or pier the mooring lines must work together as a system and share the loads to prevent any one line from being overloaded to the point of failure. This requires that they all be adjusted as needed to share any loads as close as you can get to equally as possible. Whenever there will be substantial overhang at either end, or when weather/waves/currents/ice/traffic warrant it, extra (secondary) lines must be put out well in advance, while it’s still possible to do it under relatively safe and controlled conditions. Putting out secondary lines to “help” primary lines already under moderate to heavy strain does nothing to alleviate the overloading problem, unless you have a mechanical means of taking a good strain on the secondaries that will lessen the strain on the primaries. That is why paying attention to the actual weather, and not just relying on forecasts, is so important.

The key thing to remember is that those secondary lines aren’t meant to serve as an emergency backstop for the primary lines once they’ve already failed: in effect, catching you (you hope) when you fall. They must not just hang there with slack in them so that they’ll be shock-loaded and possibly part too. Rather, they must share the load from the very beginning to prevent any lines from parting in the first place. In many cases if you part a bow or stern line the rest will follow in short order, no matter how many you have out.

This…..

…..is an example of the right way to rig the mooring lines to protect the barge’s bow from off-the-dock winds and the strong surges that often accompany the passage of deep-draft traffic in the KVK.

To take this proactive approach, however, requires that you be willing to do what some will no doubt consider to be completely unnecessary extra work up front to minimize the possibility of serious problems (read: backbreaking, dangerous work) later. This is known as the ordinary practice of good seamanship, which may not be nearly as ordinary as it should be. It’s often an equation that is hard to sell to the more leisurely among us. “Why bother?”, they’ll say. “It’s always been okay before.” Right up until it’s not.

This mentality works like a chronic, slow-acting poison and should be avoided. Confusing the apparent lack of an obvious failure with brilliant success, especially when it has become repetitive, is exactly how bad practices slowly work their way into the “ordinary” practices. Then one day, when you’ve gotten comfortably established into a deep behavioral rut, they may bite you in the ass…..

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Responses

  1. […] more » […]

  2. Excellent article as always.
    If you dont mind I’d like to use this and send it out as a safety notice ( with some minor tweaks) to some of our mariners. Primarily to remind them that this is a serious concern and so they don’t get too comfortable and forget all those of all the points you mention.
    Email me if you are Ok with that. Much appreciated.

    Igor

    Capt. Igor Loch Jr.
    Director Marine Operations
    Pacific Division
    Foss Maritime Company

  3. […] Perception, Reality & Mooring Lines: The Not-So-Ordinary Practice … […]


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