Tuesday, 8 January 2013

Chronicle of a Mooring Failure Foretold

After talking with the crew who rescued Spray when she broke away from her mooring on New Year's Day, we’re beginning to piece together what happened.  (See Out with a Bang 2)

Before we left the boat moored in the river, we knew that there was a risk of gales over the 10 days we intended to leave her hanging from the buoy.  But we had not anticipated a double-depression with Force 9 winds blowing straight up the river with no wind break of any kind over a +24 hour period.  First mistake.  We put out two new 14mm nylon lines with rubber hoses as chaffing gear, leaving enough scope on both lines so that the buoy could run well in front of the boat and not be held vertically.  The rubber hoses were fixed into the lines with tie-wraps so that they wouldn’t slide. 

The original mooring configuration.  Looks so flimsy now in retrospect...
The theory is that one of the lines was simply cut by chaffing on the (rusted) buoy ring.  The rubber hose evidently put up a brave fight but was no match for the rapid swell.  The other line, it appears, was cut by the anchor, securely fixed in its davit.  The wind and currents pushed Spray from different directions, putting her at a 90 degree angle to the buoy and pulling the line over the exposed anchor blade.  There was no chaffing gear there and it must have gone quickly.  Did not see that one coming…

For mooring in calm weather and when we are on the boat, I think our 2 line system is still trustworthy.  It’s easy to tie up to a mooring using this configuration without acrobatics of any sort.  However, to reduce chaffing further, we may replace the rubber tubing with some sort of fuzzy fabric protection, which has the added advantage of being more flexible and would allow us to tie a bowline or simple round turn directly on the mooring ring.

But for the rough stuff or anytime we intend to leave the boat unattended, we need something better.  After reviewing several books and web-sites, our favourite system that seems both sturdy and relatively easy to put into place is a slight modification of the bridle shown in the photo below, posted on the French site Hisse-et-Oh by internaute "margotte". 

Next time, with slight variations
The bridle loop is fixed to the mooring buoy with shackles (swivel would be best).  The shackles are connected to the line by two plastic hard-eye splices. The line is protected on the boat side with rubber tubing (or one of the new fabric versions), with one branch of the loop passing through the davit bow roller and the other branch fixed to the cleat (passed around the cleat with a locking figure-8 line over it).  For this bridle, we may upgrade to 14mm (4400 kg resistance) polyester (Dacron) lines instead of nylon. 

In practice, we would still use our simple out-and-back lines to tie up, then attach the bridle arrangement by leaning over the bow to fix the shackle, or by simply putting everything in place and fixing the shackle from the dinghy before going ashore.

To know how this story ends, we have to wait until 22 January when Spray will be hauled-out and inspected for damage.  It’s been a useful experience and one we will try not to repeat !  

For more articles on anchoring, visit The Monkey's Fist !