The Grounding of DEEP BLUE

 Julian 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 is correct. 

There are two other possibilities that the investigator apparently fails to consider altogether. 

1.       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. 

 2.       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.