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Old 07-17-2015, 11:58 AM   #81
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Originally Posted by Britannia View Post
That's not what I was saying. I happen to agree with you about the dynamic forces. I was talking about how wind/current forces scale up with size of vessel.

I'm certainly not disagreeing with any anchor test results.

Never mind...

Richard
Your premise before included using length for a vessel anchored at the bow...

I have no idea how the various shapes of large vessels compare to little ones and how forces affect them. But my guess is many large ships may actually have a smaller proportional head on profile (drag) than the average cruiser including sailboats that have a lot of drag from the rigging. Any available data or is someone gonna run dimensional calculations?

What is the relationship between dynamic and static forces?

Sorry to question your "math" but as I posted...what good is it if others don't believe the premise?
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Old 07-17-2015, 01:19 PM   #82
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There is a thread about photos of anchoring, in various anchorages with various anchors from different boats in the Med, on CF,Photos of Anchors Setting - Cruisers & Sailing Forums. The thread was started as a result of the many My Anchor is Better Than Your anchor "conversations."

The photos are mostly from one couple but others are adding photos. The photos are taken by people diving in the anchorage to see the how the anchors have set. Often captains technique used to when anchoring has been seen and mentioned along with the photo(s) in question.

Some lessons I have taken from that thread:
  • Many people do not properly set their anchor.
  • A chain rode and an unset anchor will hold a boat in conditions that I would not have expected.
  • A chain rode on the bottom helps hold the boat in place.
  • Some anchors are much better anchors than others.
  • Bad anchoring technique and/or inadequate anchor and anchor rode is not noticed until conditions pass a given point and this point is not seen by many boaters. They think their anchor and anchor rode is great simply because it is never really tested.
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Old 07-17-2015, 01:54 PM   #83
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Regarding the anchoring of ships, Rick Boggs just sent me this link to a document which defines how anchor and chain size is to be determined based on the formula characteristics of the ship, how the anchor is to be set (note that they say the pull of the chain or cable on the anchor should be horizontal), and a whole bunch of other definitions and requirements.

http://www.iacs.org.uk/document/publ...R_A_pdf148.PDF
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Old 07-17-2015, 02:14 PM   #84
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Re post #77, fourth paragraph,


"It may even, to a small degree help pull the anchor out. I say that because the very considerable weight of the chain straight or nearly so adds to the pull on the anchor (and the boat). Just like if you tied a line between two solid objects, measured the tension on both ends, then hung a blob of chain in the middle the tension at the ends would go up. So it must be w anchor rodes"

The notion that the weight of chain on a rode would increase tension on the anchor and help dislodge it is not right. I figured it out on my way to Starbucks. The added weight would pull the boat up a bit and equalize the tension that would be porportional to the drag of the wind or/and current. So I was out of my tree on that one.
Also unless there was enough wind to straighten out the line and chain the catenary would exist in stronger winds ... depending on how much chain weight was in the rode and where it was in the rode. But unless the anchor was on the verge of breaking out the extra catenary wouldn't do any good.

But my idea about chain weight degrading anchor performance was wrong.
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Old 07-17-2015, 02:19 PM   #85
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RickB,

Please come back...
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Old 07-17-2015, 02:27 PM   #86
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Dannc wrote;

"A chain rode on the bottom helps hold the boat in place"

I don't think so. You're thinking that the tension on the rode will be felt along the chain and the links will act like miniature anchors and help hold the boat. It won't. The chain will to some small degree relieve the anchor of the same amount of load but it's the anchor holding the boat .. not the chain. Only if the anchor was draging or on the brink of dragging would that be true.
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Old 07-17-2015, 03:21 PM   #87
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Dare I Say Another Anchor Article

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RickB,

Please come back...

The most sensible post in this thread!
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Old 07-17-2015, 03:25 PM   #88
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Quote:
Originally Posted by manyboats View Post
Dannc wrote;

"A chain rode on the bottom helps hold the boat in place"

I don't think so. You're thinking that the tension on the rode will be felt along the chain and the links will act like miniature anchors and help hold the boat. It won't. The chain will to some small degree relieve the anchor of the same amount of load but it's the anchor holding the boat .. not the chain. Only if the anchor was draging or on the brink of dragging would that be true.

Eric I find it funny you're stating these things like facts. The even funnier part is that you have about 5' of chain in your rode. So you know all about chain rodes.
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Old 07-17-2015, 04:42 PM   #89
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Quote:
Dannc wrote;

"A chain rode on the bottom helps hold the boat in place"
Quote:
Eric wrote; I don't think so.
I think it's pretty obvious that the chain lying on the bottom keeps the boat in place until such time as the pressure applied to the boat by wind and/or current lifts the chain off the bottom.

Weight is weight. It doesn't matter if it's a length of chain or an anchor or a big rock. Until that weight is moved, it will hold whatever is attached to it in place.

The photo below was taken on a day when we happened to use our trip line and float. The length of the float line was adjusted to account for the tide range, but otherwise it had no other slack in it. So it floated more or less directly above the anchor.

We always use a scope of 5:1 to 7:1. And we deploy our anchor by lowering it as we are drifting back, thus paying out the chain, and then we set the anchor using the boat. Once we've stopped backing against the rode the boat moves forward as the chain sags back onto the bottom.

The place the photo was taken is a small bay in which the current changes almost continuously. So the boat never just sits in one place unless there's enough wind to make it do that. The end result is the boat is always moving around, sometimes describing a complete circle over time.

And guess what the boat was circling on this day. Not the anchor; the boat never got anywhere near the trip line float. It circled the spot on the bottom where the chain touched down from the pulpit.

Granted, the force applied to the boat was not great. So the weight of the chain was sufficient to keep the boat in the same place more or less. The anchor, in this particular instance and all the other instances like it, played no role whatsoever in keeping the boat in place because the "strain" on the rode never overcame the weight of the chain lying on the bottom so a good portion of the chain never moved and thus never transmitted the pull of the boat to the anchor.

If the wind had come up, absolutely the anchor would have begun to play a role. The chain would have been pulled on and picked up and if the wind was strong enough eventually the pull of the boat would have been transmitted all the way down to the anchor.

But to say the weight of the chain doesn't keep the boat in place is to contradict some fairly proven principles, like gravity.
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Old 07-17-2015, 05:02 PM   #90
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Dare I Say Another Anchor Article

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I think it's pretty obvious that the chain lying on the bottom keeps the boat in place until such time as the pressure on the boat lifts the chain off the bottom.

Weight is weight. It doesn't matter if it's a length of chain or an anchor or a big rock. Until that weight is moved, it will hold whatever is attached to it in place.

The photo below was taken on a day when we happened to use our trip line and float. The length of the float line was adjusted to account for the tide range, but otherwise it had no other slack in it. So it floated more or less directly above the anchor.

We always use a scope of 5:1 to 7:1. And we deploy our anchor by lowering it as we are drifting back, thus paying out the chain, and then we set the anchor using the boat. Once we've stopped backing against the rode the boat moves forward as the chain sags back onto the bottom.

The place the photo was taken is a small bay in which the current changes almost continuously. So the boat never just sits in one place unless there's enough wind to make it do that. The end result is the boat is always moving around, sometimes describing a complete circle over time.

And guess what the boat was circling on this day. Not the anchor; the boat never got anywhere near the trip line float. It circled the spot on the bottom where the chain touched down from the pulpit.

Granted, the force applied to the boat was not great. So the weight of the chain was sufficient to keep the boat in the same place more or less. The anchor, in this particular instance and all the other instances like it, played no role whatsoever in keeping the boat in place because the "strain" on the rode never overcame the weight of the chain lying on the bottom so a good portion of the chain never moved and thus never transmitted the pull of the boat to the anchor.

If the wind had come up, absolutely the anchor would have begun to play a role. The chain would have been pulled on and picked up and if the wind was strong enough eventually the pull of the boat would be transmitted all the way down to the anchor.

But to say the weight of the chain doesn't keep the boat in place is to contradict some fairly proven principles, like gravity.

We do the same thing. Try to reverse with enough power to set the anchor and pull all the catenary out of the chain.
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Old 07-17-2015, 05:15 PM   #91
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Originally Posted by Marin View Post
Regarding the anchoring of ships, Rick Boggs just sent me this link to a document which defines how anchor and chain size is to be determined based on the formula characteristics of the ship, how the anchor is to be set (note that they say the pull of the chain or cable on the anchor should be horizontal), and a whole bunch of other definitions and requirements.

http://www.iacs.org.uk/document/publ...R_A_pdf148.PDF
Very interesting document.

One comment relative to the requirements and general certification for yachts as well. While these aren't gospel and beyond approach, they are independent. There are two levels of certification beyond standard approval. They are HHP and SHHP (High Holding Power and Super High Holding Power). It is my understanding the many Rocna anchors are SHHP. It's my understanding that many Sarca are HHP. This information is from each of their websites.

A HHP must hold twice that of a standard stockless anchor of the same mass. A SHHP must hold four times that of a standard stockless anchor of the same mass.

Now the fact some anchors are certified doesn't mean it applies to all anchors from a company. Also, the manufacturing facility must be and Rocna was once criticized for representing certification (as they were) but then their Chinese facility production not yet being certified at that time.
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Old 07-17-2015, 05:47 PM   #92
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At the risk of this being the wrong thread...

The boat I have (1983 43' Ocean Alexander) came with two anchors, a 80KGS?? and a rather large fortress. Both have 300' foot of 7/16 chain, and untold length of rope as well.

Based on the comments of the Rocna I wouldnt mind dumping the 2 anchors for 1 rocna and maybe 200' chain. It might go a long way to leveling the waterline back out (Theres a ton of concrete block in the aft trying to keep it level).

Anyone think this is a bad idea? My experience with anchors are with trailer boats and never been anchored in storms that would test one.
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Old 07-17-2015, 06:04 PM   #93
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Speaking from experience you can't go wrong with a Rocna. However you might want to think about how much rode. Depending on where you plan on anchoring and the nature of the bottom you may not need that much or you might need more.

We have 200' of chain on our boat but we really should have a least 250.' Three hundred would be even better and we'll probably do this once we start making longer cruises north.

But if where you will be anchoring is not all that deep then 200' may be just fine. You may be able to get away with less, although the chain you don't have is like the runway behind you; it doesn't do you any good when you need more.

A combination rode can work well and will certainly reduce the weight in the bow. But if your boat can carry it without compromising its trim I think an all-chain rode is the better way to go. The folks at Rocna in New Zealand emphasised the use of all-chain rode when I talked to them back in 2007 or 6 about their anchor, and the instructions that came with the Rocna we subsequently purchased also emphasized the benefits of using all chain rode with the anchor and scopes of 5:1 to 7:1.

Probably a good way to go is to talk to boaters in your area who anchor out a lot in the places you would like to go and find out what they are using for rode and how long.

If you believe that you may find yourself experiencing storms while at anchor, remember that the more rode you can let out the better because it lowers the angle of pull on the anchor which helps it stay in the bottom.
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Old 07-17-2015, 06:17 PM   #94
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I will be glad to help you ballast the boat by taking the Fortress off your hands. Send me a pm if you decide to get rid of it. However, if I was you, I would keep it, even if I had a Rocna. Good, light anchor, perfectly suited to your area. Dang, I just shot myself in the foot!
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Old 07-17-2015, 06:24 PM   #95
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Nobody mentions Mantus anchors. I see their tests beat Rocna
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Old 07-17-2015, 08:32 PM   #96
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Capthead,
I did but I'm outa here.

Talking to you guys is like beating my head against the wall.
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Old 07-17-2015, 09:43 PM   #97
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Capthead,
I did but I'm outa here.

Talking to you guys is like beating my head against the wall.
That's probably less damaging and painful than letting a big heavy anchor of any make slip out of your hands and drop on your foot... when you could have had a big but lightweight and very efficient Fortress anchor to easily kept a solid grip!
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Old 07-17-2015, 09:53 PM   #98
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"There may be trouble ahead, but while there`s moonlight and music, and love and romance, let`s face the music and dance..."
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Old 07-17-2015, 10:07 PM   #99
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I have a bet that this was going to be a hundred post thread. Come on guys. You can do it.
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Old 07-17-2015, 10:08 PM   #100
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100!


There you go Parks!
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