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Old 01-07-2015, 06:45 AM   #81
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The following article, explaining how waves are formed from a surfers perspective, is good for our consideration as it hints at how an anchorages shape and bottom topography could come into play;

How Waves Break

(Even though they're talking about ocean swell, the same physics would apply to wind waves).

Makes one consider there could be another reason why many Alaskan and BC commercial boats have 700' rodes...anchoring further out would put you in deeper water where the waves would be smaller and not as steep, especially where there are steep bottom slopes or shelves.
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Old 01-07-2015, 11:14 PM   #82
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Quote:
Originally Posted by markpierce View Post
Why when there are large areas of protected waters in southeastern Alaska?

Mark

Those are not protected waters
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Old 01-07-2015, 11:25 PM   #83
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Quote:
Originally Posted by sunchaser View Post
Mark

Those are not protected waters
I think Mark has experienced them during the cruise ship season approximately between April and August. I'm guessing a wind rose would prove that to be the calmest part of the year.
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Old 01-07-2015, 11:35 PM   #84
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No, May through September.
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Old 01-08-2015, 06:00 AM   #85
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Quote:
Originally Posted by Marin View Post
Forecasting in the PNW is pretty good when it comes to what's going to happen, not so good when it comes to when it's going to happen. We almost lost our boat to a lee shore when forecast winds arrived some eight hours before they were supposed to. And we've observed or experienced weather arriving earlier or later than forecast many times.

It's not the forecasters' fault The terrain and wind patterns here can make it difficult to accurately predict a time of arrival.

But based on over three decades of boating and floatplane flying in the PNW, BC, and SE Alaska, we have learned to regard the forecasts in terms of their predicted times the same way drivers in China regard traffic signals-- they are simply suggestions.

Particularly problematical can be the forecast times for wind shifts. What started out as the upwind side of a bay may become the downwind side before it was supposed to, and this can cause problems for boats at anchor.
this surprises me. "We almost lost our boat to a lee shore when forecast winds arrived some eight hours before they were supposed to."

Marin, as an flyer, why you would depend on a wx forecast for the safety of your boat or are you saying you have amended your ways and now know better??
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Old 01-08-2015, 11:38 AM   #86
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I know sombody that said he spent years anchoring in SE AK and it was always calm. I have as well and say it's usually calm. Chris and I went to SE in 03 and it was calm. We later heard it was the best weather in SE in 50 years. That was a magic summer. I've met people that say they went to SE and it rained all the time. They were from down south and of course it was cloudy. Californians equate any weather that's not bright and sunny as rainy.

The anchorages are small and rarely have any fetch. And the weather is cloudy (except in 03) so there's little wind. I tell stories on TF of anchoring in 50 knot winds but that is rare. Not so rare that one need'nt be prepared for it. I anchored in Windfall Harbor on a forecast calling for calm. I should have taken a clue from the name of the place but as it turned out I used my smallest anchor (a 13lb Danforth) based on the forecast but Windfall Harbor was a blow hole. There is a topographical canyon between Clarence Stright and Kassan Bay near the village of Kassan and it did blow 35 knots most of the night. The bottom must have been good and we all know the Danforth is good so we remained attached to Mother Earth. Windfall Harbor is very small though and very narrow so we were too close to the so beach for comfort but we didn't touch.

So I support Marin's notion that weather forecasts are a prediction and nothing to depend on. In our Windfall Harbor experience the calm "weather" did come to pass but localized conditions were not calm where we were due to the topigraphical conditions. In Alaska there's a saying that anyone that predicts the weather is either a fool or a green horn. But on the other hand we'd be fools not to take the weather forecast seriously (and they are very good these days) but be aware that different things can and will happen. And not only for people you see in the news. Younger people tend to think technology will save us from all evil and inconvenience but everything on this earth is relative to notions and facts alike.
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Old 01-08-2015, 12:41 PM   #87
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Some small anchorages in BC (mostly) and SE Alaska.
More often the beach - shore - rock is just as close as what you see in the picture or closer.
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Old 01-08-2015, 12:51 PM   #88
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More,
Notice all the calm water and near beaches (rock) ... also the small size of the anchorages.
The only pic that shows an anchorage open to some waves is the first in post #87. That's in Very Inlet behind Foggy Bay. It's open to Dixon Entrance that is open to the Pacific .. but only at high tide .. then the waves come over that saddle in the pic. Remember the 20'+ tides. I the 70s came over that saddle in an OB boat running from 10' seas outside surfing in to Very Inlet. We were stuck there for 5 days.
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Old 01-09-2015, 09:57 AM   #89
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Delfin...here's another take on the forces involved regarding increased load from larger bridle/dual anchor angles from a catamaran owning rock climber;

Musings on anchor bridles | Zero to Cruising!
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Old 01-09-2015, 10:22 AM   #90
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Looks like at 120 degrees the force or tension is the same on all three places. At 45 degrees the tension is split about evenly to the two anchors. Great for theory but as soon as the boat swings even a small amount one anchor loads up so the supposed advantage of taking the load w two anchors so the tension will be less on one is doubtful. And Delfin .. if you had energy multiplication you'd get 10-1 at 170 degrees. Imagine what it would be at 175 degrees.
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Old 01-09-2015, 11:08 PM   #91
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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.
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Old 01-12-2015, 08:06 PM   #92
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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.
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