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Old 08-02-2013, 11:45 AM   #61
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But still the weight of the chain reduces anchor performance by preloading the anchor. And 95% of the extra pull on the anchor would not be there w nylon rode.
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Old 08-02-2013, 11:45 AM   #62
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But still the weight of the chain reduces anchor performance by preloading the anchor. And 95% of the extra pull on the anchor would not be there w nylon rode.

Where is that dead horse thing when you need one?
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Old 08-02-2013, 11:49 AM   #63
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Where is that dead horse thing when you need one?
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Old 08-02-2013, 11:50 AM   #64
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Rick B wrote;

"Finally ... what is still missing is the fact that with adequate scope there is some amount of chain lying on the bottom. Assuminmg the bottom is flat, the catenary ends at the point the chain touches the bottom. As long as some length of chain lies on the bottom, there is no strain on the anchor."

Under what conditions? A 40' boat w 3/8ths chain in a 20 mph breeze? You bring up a very important point that is at the opposite end of the "bar tight" theory. With that 40' boat anchored at 5-1 in 40' of water and 3/8ths chain what amount of wind would just lift the chain off the bottom? But a better question would be is all the chain off the bottom in a 50 knot gale? That's where anchor performance becomes really important.

Tom yes I've done a lot of that 3-1 and occasionally 2-1 stuff and w little chain. But I always go 4 or 5-1 in a blow. All on the NW coast.
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Old 08-02-2013, 11:55 AM   #65
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Walt if you set those horses right side up you may have a horse race.

Except for AusCan this is a little like talk'in to the wall. Has anyone got anything to say that will prove or disprove my theory. And if you don't have a grip on the theory at this point you may as well get off the train.

OK enough for today. I'm waiting for somebody to start thinking and shoot down my theory. Thousands of years of boating says it must be wrong but I can't figure out why.
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Old 08-02-2013, 12:35 PM   #66
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Eric

At 3 to 1 scope using nylon in a 20 knot blow how much of that rode is off the ground, placing tension onto the anchor.

Compared to all chain in a 20 knot blow at a 3 to 1 scope ?

Change this to 4 to 1 or 5 to 1 the nylon rode will always be engaging the anchor much sooner than chain.

I might even be tempted to use a kellet on nylon rode to help give the anchor a better attack angle on the bottom at 3 to 1.

Sure at 7 to 1 a kellet is not going to add much but at 3 to 1 it will.

I know my bad but you have this backwards. Just take a look at the difference in how the rode is coming off the bow on any boat in a breeze at anchor. Chain will hold uprite off the bow when nylon will angle off.

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Old 08-02-2013, 12:56 PM   #67
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Under what conditions?
If is that critical, get one of these and start keeping records:
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Old 08-02-2013, 12:58 PM   #68
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Eric, you and I both use line/chain combo for anchoring.

Why do we put a half boat length of chain between the anchor and the line?

Chafe protection is only one reason.
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Old 08-02-2013, 01:32 PM   #69
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Thank God I'm on Manyboats "ignore list" ... phew...for a minute I thought I was loosing it.

Posted several times and referenced more ...is a study that used MATH...not guessing (well I guess all science starts with a guess), not backyard engineering thinking of cars and anchoring situtations that just don't exist...so maybe there was a "thinker" that was a missed opportunity...

Ohhhh I guess if it disagrees with you...no wonder it's on a ignore list.....but wait!

That study suggests that all chain is BAD!!!! So why would it be ignored???? I don't know..I just know the final conclusion was the same flippin' conclusion that most of us already know...that whether nylon or chain...it takes a combination of both to survive storm conditions without ridiculous amounts of scope or chain that would sink the boat.

The real thinkers know the truth is somewhere's in between ....and it depends on how you set up your ground tackle and actually use it that matters the most.

And most "trawler cruisers" usually aren't going toe to toe with storm conditions (yes there are some that see storm conditions regularly) on a regular basis so they gear up for comfortable cruising and get "extra" prepared if they have to wait out a hurricane someplace.
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Old 08-02-2013, 01:52 PM   #70
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Rick I was just ask'in.

Craig I thought the main reason chain was used on a mostly line rode was to make the line droop and lessen the angle of pull on the anchor. Like a Kellet.

psneeld You're not on my ignore list if that's what you want to know nor is anyone else. If it gets too bad here I'll just leave.
Don't recall your study. When your'e in your unhappy mode I tend to not read your posts so may have missed it that way. Sounds good though.
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Old 08-02-2013, 01:55 PM   #71
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Perhaps many haven't read the question or (more likely) don't understand it.


Here is my first attempt to explain my thinking.

"Nsail,
No there isn't. I have thought about this in the past but not to any great depth. But earlier today talking about catenary I thought about it a bit more and yes as far as I can see now it may mean that lots of chain may be reducing anchoring performance.

Consider a chain fastened to two cars. How much tension will it take to pull that chain up off the ground and make it reasonably straight? If the chain is what trawler skippers usually use anchoring at 5-1 scope as they say they do and the water was 43' deep it would require about 250' of rode. If that rode was 5/16" chain and the chain was fairly straight How much tension do you suppose it would be exerting on the 2 cars? I'm thinking hundreds of pounds but it could even be more.

Now lets imagine a trawler at anchor w the wind blowing hard. There is a lot of tension on the rode. The boat is pulling on the rode because of the wind and current (if there is any). The pull is transmitted to the anchor. But also the weight of the chain (200lbs?) is pulling on the boat and the anchor. Perhaps hundreds of pounds. So the anchor needs to resist the tension resulting from the weight of the chain AND the pull of the boat in the wind.

Nylon anchor line weighs nothing compared to chain so it would seem to me that chain on the anchor rode may have 100 or perhaps several hundred pounds of pull being exerted on the anchor that would not be there if the rode were nylon.

This pull from chain weight is probably more negative than the catenary is positive. Especially in extreme conditions. So as long as you can get an anchor to set it looks like chain would help dislodge it and the more tension on the rode the greater the force that is trying to break out the anchor.

I remember Marin swore by his "all chain rode" and thought his Bruce anchor was the reason he dragged. Perhaps he wouldn't have dragged had he had nylon?


Here is my second attempt to explain what was going over like a missed shot.


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OK nix on the cars.
Lets say you're down in the harbor and it's low tide. It's in Alaska so it's an 18' tide. You've found a pair of docks supported by pilings and they are 200' apart. You attach a chain to a piling on the north side and the south side and use a come-along to pull the chain up to the point where it's fairly straight. Perhaps 6" of catinary. Or Droop in the chain. Now there's hundreds of pounds of tension on the chain exerted to each link and to the two pilings the ends are attached to.

Now lets say the tide comes in. Is there any difference in the physics that was present at low tide? I'd say yes but not much. I think there is a small difference in the weight of the chain because water is much more dense than air. One could hang an anchor above the water and then let down until it's submerged and experience the difference. Very very little though so the tension on the ends of the chain are about the same.

The only difference between my example on the beach w the pilings and a boat at anchor is the substitution of a good solid anchor at one end of the chain and a boat at the other end w a wind blowing to bring about the necessary pull on the boat end of the chain to pull the chain up so there's 6" of catinary.

The forces are all the same and it hardly made any difference at all when the tide came in.

Now the question is whether or not there is a lot of difference in tension w the chain or w equivalent nylon line. I'd confidentially say the chain creates far far more tension.

At anchor the pull on each end of the rode from the weight of the rode is real. Part of it is from the drag of the wind or/and current and the other part is from the weight of the rode like the chain between the pilings. Lets say the pull from the weight of the chain is several hundred pounds. The pull on the anchor w nylon rode is very little compared to the chain so by using nylon instead of chain there is (I'm resisting the temptation to use the word "obviously") much less pull on the rode. So the boat using nylon under the same dynamic conditions has considerably less pull on the rode from the weight of the rode itself so can experience more drag from wind on the boat to reach the point where the anchor will break out. Clearly anchoring w a line rode is more effective.
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Old 08-02-2013, 02:07 PM   #72
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Read this....makes it all perfectly clear..

Phil posted it way back on page one and I referred to it several times...

Synthesis

I'm not saying it's all correct as it has to make assumptions too...but it correlates with every other bit of "yacht" anchoring I have experience or read so their bottom line is really close to mine...

The final point is many cruisers choose all chain for convenience....NOT necessarily anything else....but it does the job and that's all they care about.
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Old 08-02-2013, 02:23 PM   #73
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Craig I thought the main reason chain was used on a mostly line rode was to make the line droop and lessen the angle of pull on the anchor. Like a Kellet.
It is but think what I'm mainly getting at is if a half a boat length of chain induces droop or centenary like a kellet, would it not be reasonable to assume an all chain rode would do the same. Right or wrong I look at the chain in my rode as a shock absorber, if all chain was practical on my boat I'd do it. If for nothing else the shock absorbing qualities alone.

Have observed while anchored in a reasonable current my rode is tight and doubt very much of my chain is in contact with the bottom. The line stretches to absorb shock loads along with the little bit of slack undoubtedly left in the chain but I would expect far more centenary to be left in an all chain rode under similar circumstances. My unscientific 2 cents based solely on my observations.


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When your'e in your unhappy mode I tend to not read your posts so may have missed it that way.
An old adage about attracting bees with either honey or vinegar comes to mind.
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Old 08-02-2013, 02:25 PM   #74
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Eric, the big flaw in your chain theory above is the chain is attached to 2 fixed points. That does not occur in anchoring as the only fixed point is the anchor, the boat is free floating.

Edit: the link in psneeld's post above seems to vet out in my mind most of the observed observations I've made on the subject so far with great illustrations.
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Old 08-02-2013, 02:33 PM   #75
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Eric, the big flaw in your chain theory above is the chain is attached to 2 fixed points. That does not occur in anchoring as the only fixed point is the anchor, the boat is free floating.

Edit: the link in psneeld's post above seems to vet out in my mind most of the observed observations I've made on the subject so far with great illustrations.
I always use honey where I think it will do some good...
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Old 08-02-2013, 03:04 PM   #76
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I always use honey where I think it will do some good...
It only works when it's used.

Seriously though having read Eric's combo rode posts for a long while now and find him to be a reasonably intelligent man with above average savvy. In my little pea brain at least I wonder if much of this debate boils down to a big boat/small boat sorta thing? All chain is not very practical on boats 30' and under, it starts coming into its own after 32 feet in my mind. Below that the boats can really feel the weight difference on the bow. Above say 40' the line diameters increase to the point that I really wouldn't wish to mess with rope of the diameter required for the job personally.

I've read many war stories at other sites of combo rodes parting off in anchorages in places like Mexico. Owing in big part to the chafe and rocks or coral I'm sure.
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Old 08-02-2013, 03:10 PM   #77
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The distance between the two points of attachment (boat and anchor) is not an element of my "preload theory". It's the tension on the line or chain.

Given a fixed load (wind) on a boat w nylon line the boat exerts X amount of force against the rode and almost the same amount of force on the anchor.

Given the same wind (load) on a boat w chain the force against the boat is the same as is the force against the rode. But w the chain the weight of the chain causes pull on the boat AND pull on the anchor. So the load the anchor sees is the load from wind on the boat AND the pull of the chain. The pull of the chain from it's weight on the boat and anchor functions independently as if they were attached to pilings. So the pull on the anchor resulting from the chain weight is felt on the chain rode and not the line rode.

The weight of the chain pulls on both boat and anchor so one would think they cancel out and I'm sure they do but the pull from the weight of the chain is present only w the chain rode. But it is also present on the bow.


Craig wrote;

"Eric, the big flaw in your chain theory above is the chain is attached to 2 fixed points. That does not occur in anchoring as the only fixed point is the anchor, the boat is free floating."

I think you're barking up the right tree Craig. The attached point on one end is obviously the anchor and the attach point on the other end is the anchor cleat on the bow deck. The force against the boat MUST match the force (pull) on the anchor. That's a given I'd say. It seems to me now that the force would be the same nylon or chain rode. But they will differ re what AusCan says. But the load on the boat dosn't end at the bow cleat. It's passed on to the hull. I'm thinking now that the forces on the chain from the weight of the chain are felt only along the active length of the chain.

Unless someone else comes up w something better I'm going to accept that. So when at anchor in a wind the forces on the bow and anchor w a chain rode and a line rode are equal. But the forces of tension are much more along the chain itself just due to the weight of the chain.

So if two boats were anchored w one chain and the other line and both line and chain were equal in strength the chain rode would break first. Just because of the added weight of the chain.

So my theory was flawed or w/o merit. As I said before I knew it must be but just couldn't figure it out. The extra forces are contained within the active part of the chain.
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Old 08-02-2013, 04:05 PM   #78
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Why do we put a half boat length of chain between the anchor and the line?
I also anchor this way but not for the reasons one might think.

1) I don't anchor much at all.

2) since I don't, I don't like packing all that "all chain" weight around.

3) About 100% of my anchoring is for a lunch hook or an hour or two of fishing.

4) Why spend all that money on chain that's just going to rust in the chain locker due to my infrequent use.

5) My bow recovers faster when I come off a wave due to the reduced weight (I had all chain) in the chain Locker.

This same line of reasoning applies to me owning a single engine, a 32 foot boat, only 200 gals of fuel available, and a 35 foot slip. Add to that, no generator, a single state room, small refrigerator and a 3000 watt inverter.

All this supports the real mission of my boat. (Not a mission I fantasize about but never do.)
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Old 08-02-2013, 05:29 PM   #79
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Walt,

My sentiments exactly . . . . well said!

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Old 08-02-2013, 06:55 PM   #80
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Even a lot of coastal cruisers that anchor out 365 days a year (or nearly so) don't really need storm tackle aboard....

I shoot for less than 15 knots max if I'm going to anchor out (not including thunderstors or other short term events)...so I really hope to never test my gear.

Much of the reason to anchor out will involve the dingy. When above 15 knots, it gets pretty miserable and anchor out only if I'm forced to or need to save some cash...

I anchor for pleasure and boat in conditions usually where even an emergency situation will NEVER really test my ground tackle. In those situations...if I just let her run and if it piles up into a big chain ball and anchor..99% of the time it will hold me based on what I have as gear and in the condtions I usually boat in.
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