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MOORINGS
Moorings and “Why a Helix?
Moorings in the North East, (mushroom style being
the usual), have long been selected based
on the recommendation of a trusted source, such as a local harbor master,
an installer and
other “experts”. For the normal weather, their assessments
are usually good… Every so often
though, Mother Nature throws a “good one” at us that messes
everyone up. Our area had
a good blow come thru two years ago and harbors, such as Atlantic Highlands
- which lost 6
boats on moorings, suffered heavy damage.
Mushroom (and concrete block) anchors derive
their holding power as a dead weight.
It’s not common knowledge that a mushroom must be tipped over
and “set” in the same way
one “sets” a conventional anchor. Digging in is important,
otherwise it will roll and drag along
the bottom. The holding power of a mushroom that is not dug in, at best,
is twice it’s water
weight. When properly buried, it’s holding power can increase
to 10 times it’s water weight,
but once it is broken out, it will roll around on the bottom. A key
point to remember is that
everything weighs less in water, it may not float, but it does weigh
less. A concrete block
looses half it’s weight when submerged in water. Iron weighs 12.5%
less in water, so a 300
pound mushroom only weighs 262.5 lbs. in water. Therefore, it’s
maximum holding power is
2,625 lbs submerged.
 Lets
take for example, a 40-foot vessel moored in a 64 knot blow. The wind
load on
this boat will reach 5,500 pounds. While a 500-pound mushroom might
seem enough for this
boat, a 500-pound (438-pounds under water) fully dug in will resist
10 times 438 pounds or
4,380-pounds. If the load rises above this resistance, as in the example
above, the anchor will
pull out and offer little additional resistance. The boat is free and
in trouble!
Boat US Insurance, in a 2006 Hurricane Preparation
article, did an independent test in
Vineland Haven, Massachusetts on various types of permanent mooring
anchors - their results:
A 2000-pound Cement Block pulled out at 800-pounds
A 350-pound Mushroom set 5-feet in mud pulled out at 2000-pounds
A 500-pound Mushroom on sandy bottom pulled out at 1700-pounds
A 8/10 Helix in soft clay could not be pulled out by the Tug and recorded
12,000-pounds before the shackle failed. In a second test a 20,800lb
pull was recorded before
the line failed.
The cost of the Helix anchor and installation
per pound of holding power was clearly
the most favorable. Two National Marine Insurance companies offer discounts
to boat owners
and marina managers who secure their boats with a Helix mooring anchor.
A third, in it’s
pamphlet on moorings, describes our anchors as “exceptionally
effective”.
A Helix is a strong, long lived, and because
it does not drag over the harbor bottom,
environmentally friendly solution to a secure mooring. The Helix installation
is done by our
professional staff and must be hydraulically set in. We can determine
the expected holding
power by the resistance calculated during installation. A Helix shaft,
1 3/4-inch square, and
disks, are hot dipped galvanized steel. The holding shackle is 1 1/8
load rated. The “8” and
“10” in the test above refer to the disk blade diameter.
A Helix will have two or more disks,
along with extensions, depending on the soil conditions and required
holding power.
Mooring Chain
Mooring chains are an integral part of your anchoring
system that too often get neglected. It is important that you have the
proper length, thickness and installation to guarantee not only the
safety of your boat, but of those moored around you. You want to make
sure your chain length is sufficiently long enough for your harbor with
tide changes so that during a storm you do not end up with a short chain
which could result in damage to your mooring system of boat.
 As
with any metal, the links of the chain will wear over time with changing
of tides and waves causing them to grind together resulting in a chain
that no longer has enough strength to hold your boat to the mooring
during a storm. As qualified, insured divers, we can go down and inspect
the entire length of chain, link by link using lift bags to pull the
bottom chain out of the mud and determine whether the chain has wear
and warrants replacement. In some cases, we will attach the chain to
our boat and use the boat to pull it straight when it has become tangled.
Don’t take the risk of damaging your boat
or someone else's due to a failed mooring chain, have yours inspected
today!
Testing a Helix
Dosil’s Marine Services can test an older Helix for proper installation
and to determine
it’s estimated holding capacity.
What we do...
 1.
Our first action is to determine the depth of the firmer substrate and
at what depth below the “muck” layer the Helix top should
be. This requires testing the sea bottom composition down to a firm
soil. A Helix is installed with the top of the shaft about 4 to 6 inches
below the surface. This prevents the possibility of the chain wrapping
and allows the vessel to swing with the tide freely. If the Helix is
installed with the shaft rising out of the sea bottom, the chain slowly
wraps around the Helix shaft with tide swings and during a strong wind,
tightens up the chain into a knot. Now the rode begins to shorten, even
causing the boat to be moored directly above the anchor and in rare
instances, “vibrate” the Helix out with further wave action.
In installations with a deep mud layer (18 inches or less), the Helix
might require an installation deeper than the normal 4 inches.
There are different solutions available to moorings with a deep (greater
than 18 inches) light muck layer.
2. Our next step is to use a Hydraulic Power Head,
capable of delivering over a 1000 lbs of torque to measure the resistance
of the Helix to being screwed into the sea bottom. If the chain is currently
wrapped, we will unwrap the chain. This sometimes requires lift bags
and even digging the chain out of the sea bottom. There is a n additional
charge for this service. If the prior shaft installation is above the
bottom surface, we will attempt to run the shaft down to a proper depth.
In an instance where we can’t run it in further, we should still
be able gain a torque capacity. If the Helix is at the correct depth,
we will just determine the torque of the installation. With this information,
given in psi, “pounds per square inch”, we can estimate
the holding power of the Helix.
3. We will conclude with a visual inspection of the
1 inch swivel shackle and the additional
hardware connecting the chain. We will be looking for wear and check
for proper seizing, as well as freedom of movement around the Helix.
Where can we install a Helix
Dosil’s Marine Services can install a helix anywhere you would
like us to. Our crew can travel to you and set you up with a brand new
helix mooring system. Additional travel fees may apply and discounts
are available for additional work
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