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Old 30-07-2011, 11:12   #91
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Re: Q - Anchors Surface Area Comparison - Manson Supreme vs. CQR

Sorry to revive this thread, but there is a some good info in it, and I'd like to the add the following regarding soils and holding:

I'm a licensed Architect. The first thing I require from my clients (after the contract and retainer) is a soils (geologic) report.

These are prepared by a geological engineer. Many things are contained in these reports, and they effect every aspect of foundation and sub grade design.

What may be of relevance regarding anchoring is the following general rule:

As one goes deeper into most soils, the bearing value increases proportionally with depth.

Surface soils tend to looser than deeper soils because deeper soils have been compacted over eons by the weight of the soils above them. This compaction eliminates voids and increases friction between soil particles, the same way pressing brake shoes into a brake rotor creates a proportional increase in friction.

For buildings foundations, just like for anchors, it is critical that once placed, they not MOVE.

Moving buildings (settlement) cause everything from cracks and stuck doors to catastrophic structural failure, to the cliche postcards bearing that famous tower in Pisa.

So, assuming seabed strata follow the same physical laws, the deeper an anchor buries itself the greater the bearing (load carrying) capacity of the soil, and hence the greater that anchor will "hold".

But here's the problem -

I've yet to see a geological survey of a building site, even a small one, where all of the test hole samples were perfectly uniform, and yielded the exact same bearing values in laboratory analysis.

The variations might be small, and they might be large, but they are always present.

Many other factors come into play affecting bearing values - far too numerous to list and explain here, but the bottom line is, when I design a foundation system for a building, I use the worst values, then add a large safety factor, and then I say a prayer, run some calcs, select a system consistent with those calcs, the client's program, budget, building and zoning codes, and lastly, it's aesthetics.

BTW, the calculations are always based on "bearing vales vs footing area" - but anchoring is more complex - you don't get a geological report - often the bottom is obscured by murk or weed. The loads are largely dynamic, and come from many directions, not static like in buildings (except in the earth quakes I must design for here in California). Anchors must be designed for many, many different, highly variable sea beds and loadings.

That said, I own a PSC Flicka, and after much research, recently settled on a Rocna 23 on 225 feet of 1/4" G40 HT, spliced to another 175' of 1/2" brait. All this is deployed and retrieved with a Lewmar Pro-sport horizontal windlass powered by a dedicated battery.

I punched a second hole in my foredeck over the chain locker for a ventilation scoop / deck plate that can be removed and the hole used as a chain pipe when the windlass inevitably breaks down.

And why did I select a 23 lb Rockna when thier charts say 13 lbs is good for 50 knots and marginal holding for a boat of my length and displacement?

Because now, I sleep like a baby, even on short scope, in the unknown holding, 45 foot deep, windy, rolly, tiny, open ocean roadstead anchorage at Catalina's Emerald bay, while my buddy drags his 26lb CQR and Contessa 26 all over the anchorage and right into Indian Rock.

....as long as I'm anchored to windward of him.

;-)
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Old 30-07-2011, 12:52   #92
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Re: Q - Anchors Surface Area Comparison - Manson Supreme vs CQR

Nice first post, Hogan, but you have likely stirred up the ant nest again!

Everyone stand back...

And welcome to CF, mate. I hope that you have some other well thought out ideas to present in the future.

Cheers,

Jim
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Old 30-07-2011, 13:01   #93
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Re: Q - Anchors Surface Area Comparison - Manson Supreme vs CQR

Greetings and welcome aboard the CF, Hogan.

Thanks for sharing your educated opinion, and explanation of that upon which it's based.
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Old 31-07-2011, 12:13   #94
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Re: Q - Anchors Surface Area Comparison - Manson Supreme vs CQR

Thanks guys - I understand why these threads get so heated now that I've worked up to overnight anchoring.

I'm currently in Marina Del Rey, Los Angeles, and the waters of Santa Monica Bay are where I cut my anchoring and keel boat teeth.

There are no protected anchorages here, with the exception of lovely King Harbor, which I only recently figured out was permissible to anchor inside the breakwater for 3 nights, free.

Every other "anchorage" in the bay cannot even be described as "marginal" - they are "Horrible" always in at least 30 feet of water you must anchor this deep to avoid the open ocean swells and breakers, and they are ALL against a lee shore, where every summer afternoon the wind blows 15 to 20 knots (or more) against it.

Until recently, I used a 14lb delta 30 or feet of chain, and 400 feet of 1/2" nylon in these "anchorages"

(I'm preparing to cruise, and figured if I can sleep in these conditions....)

Naturally, the few times I anchored overnight in these horrible places, the wind kicked up in pitch black darkness and started howling in the rigging, forcing me a couple of times to scramble on deck in the middle of the night, start the engine, and stub my toes, chaffe my hands and break my back hauling that gear back aboard while not ending up in the breakers.

Great learning experience that convinced me to find the best anchor possible, double it's size, put it on all chain (with a snubbed rigged to BASE of my bobstay) and install a windlass.

Oh, and set a couple of anchor alarms on various GPS devices (I-Pads "anchor alert" is my fav.

And I was able to sleep like a baby believe it or not even before the hurricane strength portable mooring system now decorating my bowsprit - yea, it looks silly up there on such a small boat, but I don't drag....

My buddy (the one who dragged all over Emerald bay) is always arguing with me about the merits of his CQR -

"I DIDN'T DRAG, MY ANCHOR TRIPPED WHEN THE WIND AND SWELL SHIFTED!!!"

Yes - and it didn't reset did it?

"F*** YOU!"

(Yup, he's a sailor)

Anyway, no one wants to have even a shred of doubt about thier ground tackle - too much is at stake, so once you invest in it....you will defend whatever you have as "The Best" just to convince yourself.

That's why I upsized and overkilled everything. Even though a 13lb Rockna on nylon is overkill for a 6,000 lb 20 foot pocket cruiser 99.9999% of the time - that extra 10lbs on the bow nearly doubles the weight for penetrating hard Seabeds.

225 feet of chain means shorter scope (no matter what the eggheads say, even in storm conditions you will have a cantenary curve to it, and as it surges, the curve will increase right at the bottom (and top) pulling the anchor horizontal, and digging it in deeper and deeper with each cycle until either equilibrium is reached and the anchor stalls, or the bearing value of the seabed is exceeded and you drag - to a point more scope will prevent breakout, but not necessarily dragging - that will be a function of the afore mentioned soils variables, anchor surface area, geometry, and embedment - assuming there is no structural failure of anchor or deck hardware (I'm currently experimenting with progressive snubbers by rigging one or more softer elastic sections to a stiffer overall snubber, you should be able to dampen the loading (spread out the force over time F=MA, less acceleration (velocity increasing or decreasing with time) means less force.)

This is a principal we use in seismic design - where you have two basic options: make the structure stiff (and usually brittle as a result - see reinforced concrete) or flexible, then carefully tune it's period of resonance to avoid harmonizing with the expected forces (constructive interference).

I don't like stiff systems subjected to dynamic loading - after the next big quake hits the papers, look at the majority of buildings that collapse and trap or kill folks.

Notice anything?

Yup - they are usually concrete or brick, and often unreinforeced with (relatively ductile) steel.

The cool thing about Newtonian physics is that they are based on universal laws that apply to everything, at least at the scale we inhabit...

;-)
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Old 06-09-2011, 17:43   #95
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Re: Q - Anchors Surface Area Comparison - Manson Supreme vs CQR

Quote:
Originally Posted by Hogan View Post
Thanks guys - I understand why these threads get so heated now that I've worked up to overnight anchoring.

I'm currently in Marina Del Rey, Los Angeles, and the waters of Santa Monica Bay are where I cut my anchoring and keel boat teeth.

There are no protected anchorages here, with the exception of lovely King Harbor, which I only recently figured out was permissible to anchor inside the breakwater for 3 nights, free.

Every other "anchorage" in the bay cannot even be described as "marginal" - they are "Horrible" always in at least 30 feet of water you must anchor this deep to avoid the open ocean swells and breakers, and they are ALL against a lee shore, where every summer afternoon the wind blows 15 to 20 knots (or more) against it.

Until recently, I used a 14lb delta 30 or feet of chain, and 400 feet of 1/2" nylon in these "anchorages"

(I'm preparing to cruise, and figured if I can sleep in these conditions....)

Naturally, the few times I anchored overnight in these horrible places, the wind kicked up in pitch black darkness and started howling in the rigging, forcing me a couple of times to scramble on deck in the middle of the night, start the engine, and stub my toes, chaffe my hands and break my back hauling that gear back aboard while not ending up in the breakers.

Great learning experience that convinced me to find the best anchor possible, double it's size, put it on all chain (with a snubbed rigged to BASE of my bobstay) and install a windlass.

Oh, and set a couple of anchor alarms on various GPS devices (I-Pads "anchor alert" is my fav.

And I was able to sleep like a baby believe it or not even before the hurricane strength portable mooring system now decorating my bowsprit - yea, it looks silly up there on such a small boat, but I don't drag....

My buddy (the one who dragged all over Emerald bay) is always arguing with me about the merits of his CQR -

"I DIDN'T DRAG, MY ANCHOR TRIPPED WHEN THE WIND AND SWELL SHIFTED!!!"

Yes - and it didn't reset did it?

"F*** YOU!"

(Yup, he's a sailor)

Anyway, no one wants to have even a shred of doubt about thier ground tackle - too much is at stake, so once you invest in it....you will defend whatever you have as "The Best" just to convince yourself.

That's why I upsized and overkilled everything. Even though a 13lb Rockna on nylon is overkill for a 6,000 lb 20 foot pocket cruiser 99.9999% of the time - that extra 10lbs on the bow nearly doubles the weight for penetrating hard Seabeds.

225 feet of chain means shorter scope (no matter what the eggheads say, even in storm conditions you will have a cantenary curve to it, and as it surges, the curve will increase right at the bottom (and top) pulling the anchor horizontal, and digging it in deeper and deeper with each cycle until either equilibrium is reached and the anchor stalls, or the bearing value of the seabed is exceeded and you drag - to a point more scope will prevent breakout, but not necessarily dragging - that will be a function of the afore mentioned soils variables, anchor surface area, geometry, and embedment - assuming there is no structural failure of anchor or deck hardware (I'm currently experimenting with progressive snubbers by rigging one or more softer elastic sections to a stiffer overall snubber, you should be able to dampen the loading (spread out the force over time F=MA, less acceleration (velocity increasing or decreasing with time) means less force.)

This is a principal we use in seismic design - where you have two basic options: make the structure stiff (and usually brittle as a result - see reinforced concrete) or flexible, then carefully tune it's period of resonance to avoid harmonizing with the expected forces (constructive interference).

I don't like stiff systems subjected to dynamic loading - after the next big quake hits the papers, look at the majority of buildings that collapse and trap or kill folks.

Notice anything?

Yup - they are usually concrete or brick, and often unreinforeced with (relatively ductile) steel.

The cool thing about Newtonian physics is that they are based on universal laws that apply to everything, at least at the scale we inhabit...

;-)
"Pride Gowith Before A Fall"
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Old 06-09-2011, 18:33   #96
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Re: Anchors Surface Area Comparison - Manson Supreme vs. CQR

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Originally Posted by Don Lucas View Post
I think CF should send out an invite to every anchor manufacturer to a forum discussion battle! I bet this would become a good read, but in the end we wouldn't know much more than when it started! But we could always hope!
Hey! I think there might be a game shoe in this.
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Old 07-09-2011, 09:53   #97
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Re: Anchors Surface Area Comparison - Manson Supreme vs. CQR

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Originally Posted by perchance View Post
Hey! I think there might be a game shoe in this.

Well then, if the shoe fits, air it.
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