Storm Mooring

JHH5-12306I have written in the past about our distrust of moorings and how we generally prefer to be on our own anchor when the winds blow hard. However, there is one exception to that rule: our own mooring at our Base Camp. We just had it checked and took some photographs of the process, which show how the mooring that Morgan’s Cloud has ridden out three hurricanes on is built.

Checking It Right

We believe that the only right way to check a mooring that is sunk in soft mud, like ours, is to lift the whole thing every five years.

JHH5II-16158

It takes some serious gear to lift a mooring comprised of two 4000 lb (1800 kg) granite boulders.

Granite is Good

In our area, where the use of old metal parts like fork lift counter weights (our mooring in Bermuda) is banned, many people use concrete blocks, but we prefer granite because it loses less of its weight when submerged.

JHHG3-1000411

Here comes the first boulder.

Attachment

A hole was drilled right through each of the boulders to take a 1-1/2” (38 mm) diameter steel bar with an eye on one end that the ground chain is attached to with shackles that we had welded closed—no plastic wire-ties here.

Laid Carefully

We carefully laid the two boulders about 20-feet (6 meters) apart in-line with the one nautical mile longest fetch. The ground chain is attached to the up chain, then to the first boulder and from thence to the second boulder. We debated setting up the mooring with the up chain attached at the midpoint between the boulders but decided that, in our case where the fetch from all but one direction is a matter of yards, in-line arrangement would be better.

JHH5II-16192

Checking the joint between the 30-feet of 1-1/2” ground chain and 25-feet (7.6 meters) of 3/4” (20 mm) up-chain.

The mooring is in 20-feet of water at high water springs and we allowed for another 5-feet of storm surge.

All Chain is Not Equal

The ground chain is salvaged ship’s anchor chain that has lasted for five years with almost no deterioration.

When we initially laid the mooring we were only able to source, here in Nova Scotia, some no-name chain for the up chain. It was amazing how quickly it corroded; so the next time we drove to Maine, we picked up some American-made Acco chain, which, after three years, still looks brand new. All the shackles are American-made from Crosby and have held up well.

Annual Check

We check down to the joint between the ground and up chains every year by hauling it to the surface using our massive windlass. We attached the swivel at the top of the up chain, just under the buoy, where we can check it frequently, rather than at the joint between the ground and up chains, which is more common practice but harder to check. (I have seen two moorings fail due to the weld holding the nut on the swivel corroding through.)

Winterizing

We winterize by removing the mooring ball and attaching a small and robust fish-farm float—which stands up well to the up to three feet of ice that we can get in our inlet—on a length of line so that all the chain is lying in the mud, which seems to result in significantly less wear and corrosion on the up chain than leaving the mooring in its summer configuration, as many do.

Guard Against a Fumble

I have attached a deep water trawl float on 4-feet (1.25 meters) of line to the joint between the ground and up chains in case we ever lose the upper end while winterizing the mooring. An eventuality that, without this buoy that could be easily found by a diver, would certainly result in losing the whole works forever in the deep mud.

Now you know why we say that the Morgan’s Cloud motto is “if it’s worth doing, it’s worth doing to excess”.

How is your mooring constructed? Please leave a comment.

Further Reading

{ 9 comments… add one }

  • Nicolas May 30, 2012, 7:26 am

    Perfect no-nonsense mooring. Big deal, really!!

    A suggestion. If using a swivel, how about above the buoy, dangling in the air between the water and Morgan Cloud’s stem?

    I test my mooring 2x a year by going forward, then going in reverse at full power. At tether’s end, the bow snaps down quite a bit. At this point the force exerted by the 16 ton boat must be quite considerable.

    Also I dive every other year, but cannot inspect or retrieve the 6 ton concrete block buried in mud. Ship’s chain that is visible tells me that ship’s chain in the mud is OK.

    Reply
    • John May 30, 2012, 10:08 am

      Hi Nicolas,

      Sounds like yours is even bigger than ours! As you say, seeing the up-end of the ground chain in good shape is comforting. However, it does not tell you what shape the hardware that attaches the ground chain to the weight is in. Taking a look at that was our major reason for hauling the boulder. We have friends that nearly lost their boat when the shackle attaching the ground chain to the weight failed after 10 years without inspection.

      On the surge test. I too have to tested things like that. However, I have always wondered whether or not it was a good idea. Could it be that since we can’t see the things that we are testing and check them for deformation, maybe we risk stressing some part of the system so it is close to failure without knowing it, to the point it will fail later? Not sure. Anyone have any idea? Matt?

      Interesting idea on the buoy. However it only takes us 10 minutes to haul the swivel out of the water, so I think we will leave it as it is.

      Reply
      • Matt Marsh May 30, 2012, 4:29 pm

        Re. surge test (backing down the boat at full throttle)

        If the mooring fails this test, the answer is obvious.

        If the mooring holds, though, that doesn’t necessarily mean it’s up to snuff.

        Let’s say you put a 12 m (40′) sloop in full reverse, and her bow drops by two feet when the chain snaps tight. Typical moment to trim on a boat this size would be around 130 kg.m/cm, and the chain pulls on the bow, 6 m from the centre of flotation. So the moment is (130kg.m/cm * 60cm * 9.81m/s2) = 77 kN.m, and the bow-d0wn force on the anchor roller is (77kN.m / 6m) = 13 kN. We might have roughly 1.4 to 1 scope (~45 degrees) for a mooring, so that gives (13 / sin45) = 18 kN of tension on the chain….

        ….which will have no visible effect on anything heftier than 7mm (1/4″) G40 chain. Most of the boat’s kinetic energy was used up in lifting the chain off the seabed, and in forcing water out of the way to let the bow down.

        Now, granted, the peak dynamic load will be a bit higher than in this static analysis, but the point is this: The boat under engine can create only a fraction of the loads that a 6-foot wave will create when it lifts her up and back, breaking over the bulwarks as the chain goes bar-tight. The only way I know of to simulate that load is to have a much larger boat pull on the chain so hard that the mooring block lifts off the bottom…. at which point you’re already hauling the thing up, so you may as well look at it.

        Reply
        • Matt Marsh May 30, 2012, 4:33 pm

          PS – I wouldn’t be worried about shock loading the components by doing a surge test in full reverse. If your boat under engine can create loads- even shock loads- anywhere close to the yield point of the steel, the mooring will be so obviously undersized (or so badly corroded) that you’d be afraid to tie off to it in the first place.

          Reply
          • John May 30, 2012, 5:18 pm

            Hi Matt,

            Problem is, of course, that in a case where the mooring is not lifted all the way, one would not know that.

        • John May 30, 2012, 5:13 pm

          As I have said before, engineers rock! So often what seems obvious to those of us without engineering training is anything but.

          I’m a technician by trade, so I have just enough knowledge to know that very often I don’t know.

          Thanks, Matt.

          Reply
        • Nicolas May 31, 2012, 4:29 am

          Wow, thank you Matt & John. This is absolutely excellent stuff. Yes it is obvious that 6′ surging waves will far exceed the force exerted by going in full reverse.

          In F11 at my mooring the waves don’t go over 2 or 3 feet, which still is a lot more forceful (wind plus waves) than going in full reverse.

          Guess I need to send a diver down, to dig his way thru the mud down to the shackle connecting the cement block to the chain, for inspection. We don’t have the facilities for mooring haulout in this small town.

          Reply
  • Geir Ove May 30, 2012, 7:58 am

    Lower grade steel that is used, the less it will rust, High grade steel, rust a lot faster,
    Just go up in dim, and down in grade, it will be OK, for a very long time.

    Reply
    • John May 30, 2012, 9:57 am

      Hi Geir Ove,

      That’s interesting and makes sense. There are iron (as apposed to steel) barges that have lasted for a very long time.

      Reply

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