I've been a commercial operator since 1984. I regularly cross Cook Strait from Wellington to Marlborough sounds in all sorts of weather.
My present boat which I had built and was launched in 1993 is a 22m by 6.2m displacement launch she weighs 60tonnes and is used for Functions and Expeditions. We are regularly anchored in 30-50knots sometimes a lot more.
My ground tackle is Manson 220pound Plough shackled to 130meters of 16ml stamp chain. My spare is also a 220 pound Plough with 20m of 16ml chain and a 200m coil of 32ml nylon rope.
Twice in recent years I've been caught out in storm force winds both in Port Gore with divers aboard.
Melville cove is where we have anchored. There is no sea but the gusts are ferocious 90+ knots.
Special care must be taken with battening down and stowage as the wind can heel the boat a lot when the chain snaps on the bollard and she rides up to the anchor again.
I have found on a 5-1 ratio in 15-20m of water in extreme conditions my Manson plough has never let me down.
I've found the hardest part is pulling the anchor up the next day as the shoulders and shaft and sometimes chain is buried. So the chain must be shackled when above the anchor and driven over the top. It's in so hard sometimes you can feel the bow pull down when going over the top (not a bad complaint) I would say that the harder it blows the deeper the anchor will dig in.
I could not imagine with the right anchoring technique that a plough would let go.
Paul Gubb NZCM