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Old 07-15-2015, 09:42 PM   #21
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Here is an interesting compilation of some of the anchor tests.

Independent Anchor Performance Testing
Compiled by the inventor of the Rocna. No judgments here - just full disclosure.

Richard
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Old 07-15-2015, 09:46 PM   #22
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Are you guys saying that no load is on the anchor until all the catenary is out of the rode? That doesn't sound right. The catenary keeps the pull more horizontal but the load is still on the anchor.
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Old 07-15-2015, 09:53 PM   #23
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Compiled by the inventor of the Rocna. No judgments here - just full disclosure.

Richard
Thanks for disclosing.
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Old 07-15-2015, 10:20 PM   #24
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Sigh. There are two different methods of anchoring. Drag enbedment and tension anchoring.

Theoretically, a drag enbedment anchor merely holds the end of a centenary chain. Long enough chain, no anchor required.

A tension anchor requires the use of a well placed anchor with a cable or rope rode.

They use entirely different physics.

Eric, the short scope ratio anchors you prefer use tension. The rest of the big boats with bohunking metric f-tons of chain can get away with a chain catenary and an anchor at the end.

I have pulled up ships moorings that have no anchor, just a lot of chain which provides a lot of drag in the mud.

Indeed, I know of a sub that anchored successfully with chain only, as the anchor was cut off, as it was banging on the ballast tanks like a gong.

Eric, please look this up. Your arguments have merit, but only when your comparisons are the same.
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Old 07-15-2015, 10:54 PM   #25
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Originally Posted by hmason View Post
If you are upwind of me please use a Rocna or a Manson Supreme. If you are downwind, I don't care what you use.
Yes…but don't forget, in tidal areas, downwind often later becomes upwind.
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Old 07-15-2015, 11:13 PM   #26
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So here's a question...... Why does this work (photo)?

Everybody here talks about how one needs a big anchor, bigger is better, right?. Eric believes that if we'd had a 44# Bruce instead of the manufacturer-recommended 33# we wouldn't have had the dragging problems we had. I find it hard to believe that 9 pounds is going to make any difference to the anchor's ability to stay put when pulled on real hard but who knows? People believe an all-chain rode isn't necessary or is even bad.

So why do all these arguments fall totally apart in the situation illustrated below? Compared to the size of the vessel, the anchors on this thing are not just small, they're miniscule, a joke. Same with the chain. Sure, they're massive and heavy when you walk up to them. But compared to the size of the vessel the anchor's a bent paper clip and the chain is a piece of string.

If we scaled this ship's anchor and chain up so it was the same ratio to the vessel's size as the anchor and chain on, say, our boat, the anchor would be damn near the size of a 737. Well, not quite but you get the idea.

So why do the ridiculously tiny anchor and chain on this vessel work?

I'm not trying to win an argument or defend a point. I genuinely don't know, particularly if the same rules apply to all vessels across the board.
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Old 07-15-2015, 11:35 PM   #27
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Good question Marin, and one I've often thought about, and even quoted as a case that proves the added benefit of the all chain rode, basically. I think the key is that the links in the chain on these boats weigh about a ton, (give or take, depending on the vessel size), and the anchor just sort of grabs the seafloor enough to locate the end of the chain I think. Sure, the anchor will dig in as well, but I suspect it is the huge catenary which does the real holding, and to me this is a good example of that principle in action.
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Old 07-15-2015, 11:57 PM   #28
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Originally Posted by BandB View Post
Here is an interesting compilation of some of the anchor tests.

Independent Anchor Performance Testing
BandB,
How could it be "independant" when it says "Peter Smith" at the top of the page in the web page window. Can't imagine anybody more biased about the Rocna anchor that Peter Smith.
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Old 07-16-2015, 12:07 AM   #29
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...
If we scaled this ship's anchor and chain up so it was the same ratio to the vessel's size as the anchor and chain on, say, our boat, the anchor would be damn near the size of a 737. Well, not quite but you get the idea.

So why do the ridiculously tiny anchor and chain on this vessel work?

...
But is that actually true? Let's run some numbers.

Here's a short article on anchor chain on the Triple E class freighter from Maersk

Anchor chain for the world’s largest ship is so big it makes humans look like mini figurines | 22 Words

It says that the links on the anchor chain weigh over 500 lbs each. Now the links on my anchor chain weigh 0.25 lbs each (8 links to the foot, 2lbs per foot). That makes the chain on the container ship 2000 times heavier than my boat.

The Triple E class container ship runs 55,000 tonnes displacement empty (https://en.wikipedia.org/wiki/Maersk_Triple_E_class) My boat is 31 tonnes dry, making the Triple E about 1800 times heavier than my boat.

It seems to me that the anchor chain, at least, appears to be roughly in scale to the size of the boat/ship.

I haven't found the weight of the anchors for these behemoths yet.

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Old 07-16-2015, 12:10 AM   #30
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Funny how he omiits the SARCA from even being discussed or tested
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Old 07-16-2015, 12:15 AM   #31
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Peter---- Yes, but...... Compared to the size and weight of the vessel a chain made up of one-ton links is still light and tiny. And look at the windage of the thing. Sure, its tremendous weight gives it an inertia that takes time for the wind to overcome. But it will eventually overcome it and move the ship around.

Now I'm absolute rubbish at math, so correct me if I did this wrong. A 44 pound anchor is .0014 percent of 30,000 pounds, which is the weight of our boat. A tanker that weighs 400 million pounds (200,000 tons which seems to be the average size for a typical large tanker--- but not an ultra large one) would also need an anchor that weighs .0014 percent of its weight, which would be 560,000 pounds, or 280 tons. Now maybe the anchor of a ship this size weighs that much, I don't know. They don't look it, though....
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Old 07-16-2015, 12:21 AM   #32
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You have 450' of cable? Damn. That sounds like a lot.
Not exactly. I have 120' of chain and (from memory) 320' of cable. But I could be mis-remembering. 😀
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Old 07-16-2015, 12:26 AM   #33
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BandB,
How could it be "independant" when it says "Peter Smith" at the top of the page in the web page window. Can't imagine anybody more biased about the Rocna anchor that Peter Smith.
It obviously isn't. I didn't know the history. And the Independent is just the link as it posts. But actually the tests themselves may or may not be independent. One would have to decide that. I'm sure given the situation, he didn't include tests that reflect badly on Rocna.
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Old 07-16-2015, 01:27 AM   #34
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Funny how he omiits the SARCA from even being discussed or tested
Unsurprising. It could complicate things.
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Old 07-16-2015, 01:48 AM   #35
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Unsurprising. It could complicate things.
Yea, it's no fun at all to compare your anchor in a "unbiased" test with another anchor that is in the same category.

Omit the competition to make yourself look better???

Funny because the side by side tests I saw that The SARCA inventor put on at least had the Rocna anchor in them, even though they showed the Rocna to be a pretty good anchor itself!
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Old 07-16-2015, 02:05 AM   #36
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Yea, it's no fun at all to compare your anchor in a "unbiased" test with another anchor that is in the same category.

Omit the competition to make yourself look better???

Funny because the side by side tests I saw that The SARCA inventor put on at least had the Rocna anchor in them, even though they showed the Rocna to be a pretty good anchor itself!
Yes, but, shockingly, the Sarca tests show the Sarca topping the Rocna. lol.
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Old 07-16-2015, 02:05 AM   #37
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Sarca doesn't go beyond 320 lbs do they? So no classed boats beyond 100' or so? I know Rocna builds up to 606 lbs and even beyond if required.
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Old 07-16-2015, 02:28 AM   #38
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But is that actually true? Let's run some numbers.

Here's a short article on anchor chain on the Triple E class freighter from Maersk

Anchor chain for the world’s largest ship is so big it makes humans look like mini figurines | 22 Words

It says that the links on the anchor chain weigh over 500 lbs each. Now the links on my anchor chain weigh 0.25 lbs each (8 links to the foot, 2lbs per foot). That makes the chain on the container ship 2000 times heavier than my boat.

The Triple E class container ship runs 55,000 tonnes displacement empty (https://en.wikipedia.org/wiki/Maersk_Triple_E_class) My boat is 31 tonnes dry, making the Triple E about 1800 times heavier than my boat.

It seems to me that the anchor chain, at least, appears to be roughly in scale to the size of the boat/ship.

I haven't found the weight of the anchors for these behemoths yet.

Richard
Emma Maersk (similar size E series ship) has a 130 tonne anchor. My anchor is 50 Kg. Emma's anchor is 2600 times heavier than mine. Still seems like we're in roughly the right ballpark for size.

Richard
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Old 07-16-2015, 03:26 AM   #39
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Sarca doesn't go beyond 320 lbs do they? So no classed boats beyond 100' or so? I know Rocna builds up to 606 lbs and even beyond if required.
Clicking "Anchor Right Products" on the Anchor Right Australia website, brings up a group of pics of boats with anchors. One pic appears to be of a fair sized ship, in dry dock, but I could not get it to load and enlarge.
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Old 07-16-2015, 04:25 AM   #40
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Here is a link to a document setting out a few anchor parameters.

https://www.amsa.gov.au/forms-and-pu.../NRIP00092.pdf
Chapter 3 is the interesting part.

For Marin and others who wonder about ship anchor sizes, the standard defines 'Equipment number" and gives an equation with a number of variables. Basically Equipment number is a function of displacement, frontal area and profile area.

In addition, a document from a Wollongong, NSW workshop held in 2014 that considered the impacts of anchoring off coal ports whilst waiting to be loaded contains some items of interest. The document"Anchors aweigh: workshop summary" included the statement below as part of their overview of anchoring.

Anchor designs are numerous, however, the weight of the cable, or anchor chain alone ultimately hold the ship in position. A ratio, relating to the length of anchor chain to the water depth varies depending on the size of the vessel, from 3-5:1. Each link ~200kg contributes to an anchors holding capacity. Depending on ocean currents and wind, ships may swing around the point at which the cable rises from the seabed.
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