,During the night of 2 August there was a massive blow in Auckland causing quite a bit of havoc ashore including fallen trees and downed power lines. I recall lying in bed listening to the gusts thankful not to be out on our boat.
Hobsonville marina emailed us the next day advising of gusts up to 67 knots in the marina with some vessels suffering damage to canopies and hatches. Di and I went there to check on Rapport, fortunately finding everything was fine.
Sir Peter Blake’s former 36 metre alloy expedition yacht Seamaster, now called Archangel, which has been anchored for a long time off St Heliers Beach dragged her anchor, but fortunately beached with apparently no damage. Her current owner says Archangel had a heavy anchor and 100 metres of chain out, but there are two issues of interest here:
1. Her owner was not aboard, but able to tell remotely that Archangel had dragged and therefore able to go and investigate. I don’t know what technology the owner was using, but see our last posting re Anchor Watch HD as it shows how valuable this free app can be.
2. Her owner says Archangel dragged her anchor due to a 180 degree wind shift. This is a point I have mentioned many times, that is with adequate ground tackle set (as Archangel had) you are most unlikely to drag in a consistent wind. However when you encounter a 180 degree wind shift – which often happens during storms and/or as fronts pass through, all bets are off. This is because your boat’s movement following the wind shift can pull your anchor out from its set position and just drag it across the seabed. In other cases as your chain moves in the opposite direction it may foul the anchor and drag it across the seabed preventing it from resetting.
But wait there’s more. You have almost certainly anchored on a weather shore, that is with your bow pointing to the shore and no matter how hard the wind blows you are unlikely to see wavelets more than about 25cm high. After the wind shift you will be on a lee shore, that is with your stern pointing to shore and in shallower water. Now the wind has much greater distance to create waves and these can quickly rise to a metre or more. Waves cause a jerking motion placing further strain on your anchor and compromising your security.
Lesson: a 180 degree wind shift is always a case for concern and for close monitoring of your situation.