my best storm anchor technique

[Djbangi]

MurrayM, as another rock and ice climbing catamaran owner - I'm afraid that Manyboats post has the same conclusion as I do, that as the vessel yaws first one anchor, then the other, effectively take all the load. As it swings through the 'centre' your diagram is (I am convinced) correct but most of the time you are effectively reliant on one anchor.

However the maximum loads on the anchor(s) are snatch loads, caused by yawing simultaneous with moving fore and aft as the wind eases and gusts. A bridle or 'V' anchor arrangement reduces yawing and this reduces the overall level of snatch loads.

So its not so much that the anchors (or bridle) share the load nor that each anchor or bridle arm only is stressed half the time but the 'V' anchor arrangement or bridle actually reduces the maximum loads because yawing is reduced. There are other ways to reduce yawing, a riding sail is a perfect example for a Trawler. Deploying one anchor as 'normal' and simply deploying a second such that it simply drags under the bow is another well recognised technique. Tying to trees (or rocks) is another.

But its all about what is best at the time, for you, the vessel and the location - its back to that compromise.

 

[Djbangi]

Anchor Right have an interesting link describing a vessel exposed to Storm force winds.

Quo Vadis Sits Out Force 10 on Anchor Right | Anchor Right News and Updates

The vessel (sorry but its not a trawler), Quo Vardis, in question is a 20t steel ketch, 43' long that sat out a storm (winds recorded by the local coastguard at over 50 knots for over 6 hours) in the UK's River Mersey just down stream from Liverpool Docks, now converted to a marina. The owner was nearing completion of a UK circumnavigation, single handed, but arrived in the river too late to enter the locked marina. He was aware of the impending storm and anchored just down river from the marina lock gates. He anchored at mid tide on an outgoing tide at 3am and the story, ended at 9am again mid tide on the incoming tide. The river can flow at 5knots. The river faces NW directly into the storm. Further downriver 2 -3 NM there is a breakwater that covers at mid tide - so during the 6 hours at anchor the breakwater provided some shelter, the images on the AR website are at the point when the breakwater is 'losing' its protective benefits. The images are taken by a local birdwatcher who was passing - and he gave the images to the RNLI.

Normally I would not link this type of story - there are too many reasons why the story might have been embellished. However I was in the UK soon after the story was aired (it hit TV, local newspapers and radio) and I visited the RNLI station that was directly involved (and had a day with the volunteers who had actually been involved). I also questioned the owner of the Quo Vardis to clarify some of the details. Most of the salient points are confirmed by the crew of the lifeboat.

The interesting facet is that the 20t Quo Vardis sat at anchor using a 25kg anchor (SARCA No7) in 50 knot winds for 6 hours - and did not move. The yacht was on an all chain rode, no snubber. The vessel is 'heavy' and has fair windage. The location was fully exposed to the wind, its basically open sea and ocean till you get to N America, and enjoyed some shelter, from seas, for most of the time (but not when the images were taken).

To me the anchor seems slightly undersized but contradicts the mantra that 'bigger is better'. But there again our anchor on our own vessel would also be considered 'undersized'. The owner was more than happy with the performance of his anchor and would not upsize. The RNLI were also impressed with the anchor's performance (though on their new lifeboats (that replace the big one in the images) - their Shannon Class, they are exclusively equipped with steel Spades).

I can confirm that the involvement of the RNLI was accidental. They were called out to look for 3 teenagers seen on the river (but then found safe and well). The 2 lifeboats, from 2 different stations, saw the Quo Vardis and offered assistance, which the owner accepted but only because the larger lifeboat suggested that if they did not move the Quo Vardis they would sit alongside until the storm eased - moral pressure encouraged acceptance of help!

This is just one story, but the detail has been confirmed (as well as I could). There are a few nuances that remain unanswered - like why did the owner anchor there and not 2nm further upstream where there was much more shelter etc - but he was there and I was not, his call. And if he had anchored elsewhere - there would not be a story.