The Grounding of DEEP BLUE
Buesnel of Blue Water Supplies writes:-
The case of the grounding of Deep Blue is not as simple
as it first seems. A New Zealand Maritime Safety Authority Accident
Investigation Report investigated by Jim Lott, NARB, concluded that “the
anchor failed when the bolt securing the two parts of the anchor fell out”
and “that this could reasonably be attributed to the failure of the nut
that secured it”. What the investigator seemingly failed to
consider is how this could have possibly occurred when the nut used is
specifically designed not to unscrew and there were no forces acting on it
at the time.
Spade anchors are designed to dismantle into two pieces
for easy stowage, a very popular feature. The shank is inserted into a
socket on the blade and retained by a stainless steel bolt with a “Nyloc”
style nut. During normal operation there is no load on this bolt as
the substantial socket assembly takes all the force. At boat shows we
often demonstrate this by removing the bolt completely and pulling the
anchor as per normal operation. Even when “break out” is simulated the
shank remains inserted in the socket clearly showing that the bolt simply
holds the two sections together.
“Nyloc” style nuts are used extensively to prevent
accidental loosening of nuts, normally associated with high vibration
situations. In the case of the Spade, there is no turning force on the
bolt/nut combination and little or no vibration, “Nyloc” style nuts
are used as a precautionary measure to totally eliminate any chance of the
nut coming loose. “Nyloc” style nuts require tools and significant
force to tighten or loosen them. If the nut was initially tight, and there
were no forces acting on it to loosen it, it could not have come undone.
In my opinion, it is extremely unlikely that the investigator’s conclusion
There are two other possibilities that the investigator
apparently fails to consider altogether.
The nut was never tightened properly in the first place.
This is a distinct
possibility as the anchor was relatively new, was purchased assembled and
was not subsequently disassembled. When the Spade anchor was
displayed, it is possible that the bolt was only loosely fitted, as
purchasers often wish to dismantle the anchor for transport. (“Nyloc” style
nuts are designed to be used only once). It is possible that the
owner/skipper failed to ensure that the bolt was tight.
The nut, bolt and blade were removed after the grounding.
Apparently no attempt was made to recover the
anchor until three days after the grounding. During this time somebody
could have removed the blade. It should also be noted that the vessel
was not insured and that the owner/skipper is allegedly attempting to claim
$60,000 for a 27-year-old vessel he purchased two and a half years
previously for only $7,000. *
There are a number of other
peculiar facts in the case:-
The owner was at the top of the mast fixing the tricolour
light at 2:30 am when the vessel grounded. The vessel had been at sea
for 7 days having encountered rough conditions. They had anchored at
22:30 and then spent two and a half hours providing radio communications for
an emergency and helicopter evacuation nearby. It is logical to assume
that the crew would be tired. The investigator apparently failed to
consider that this could have been a contributing factor.
Why was no anchor watch maintained even though all three crew
were on deck?
Even if the anchor blade had become separated from the shank,
the shank and chain alone would have been able to hold the vessel under the
weather conditions of the time. *
The vessel was apparently anchored too close to the shore and
unprotected from the onshore wind. *
The investigator concluded that the rope/chain combination was
sufficient as the ratio was 3.25:1. He failed to take freeboard into
account, which would reduce the ratio to approximately 2.88:1. Whilst,
according to the report, 3:1 is commonly considered adequate in calm
conditions, this was below that and well below recommendations especially if
no anchor watch is to be maintained.
In my opinion, any combination of factors could have lead to
Deep Blue dragging including the lack of adequate scope, but the failure to
maintain an anchor watch was the primary cause of the grounding.
Despite doubts over the case, Spade have agreed to
modify future bolts, as recommended by the investigator, to include a pin
after the nut and a note advising that “Nyloc” style nuts should only be
used once. (There is no need to replace the nut after each deployment
as reported by PBO, but every time the anchor is dismantled). Existing
owners are advised that if they have any concerns about their nuts, that
they arrange for the end of the bolt to be drilled and have a pin and new
“Nyloc” style nut fitted. It is the owners’ responsibility to ensure
that the nut & bolt (or alternative) are in good condition, secure and
suitable for the purpose. It must be emphasised that thousands of
Spade Anchors have been sold and that no similar cases have been reported.
Please contact Blue Water Supplies on 01534 739594.
*Information provided by Alain Poiraud – chairman of
SPADE and inventor/designer of the SPADE anchor.