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Old 26-07-2020, 12:25   #31
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Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?

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Originally Posted by MicHughV View Post
to me the issue is kinda moot.

in any anchorage you are likely to get a dozen or more boats...different lengths, different hulls, different skippers, etc, ad infinitum.

no two boats are likely to have the same anchorage system, be it rope, chain or any combo of the above, and anchor types can run from one extreme to another and each skipper is likely to deploy what has worked best for him, be he a pro or a newbie, using one anchor or two, etc, etc. On the far end of the scale, bottom holding is a topic all of it's own.

some will use 10:1 scope others 5:1, etc, etc.

some boats swing to an anchor and some are rock steady.

there is simply not a one size fits all here...

I know what works best for me and it's the same system I've used on different boats over 40 years and no amount of discussion, modeling, formula's, theories, or otherwise is likely to have me change anything.

I don't think I'm alone in this view.

Right. This thread was not about your boat type or cruising style.
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Old 26-07-2020, 12:29   #32
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Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?

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Originally Posted by Thumbs Up View Post
I am not knocking the splice itself, I have redone mine a few times due to a rusty looking end link although some chain rope combinations are very hard to splice (big line vs. short links) The problem is handling the rope portion. On my windlass you have to get all of the rope stuffed into the hole, along with the splice before you can get the chain onto the gypsy. It would be easy to lose a finger in the process. With all chain, a windlass, and a cockpit switch you pretty much have remote control of the anchor, an enviable feature (but has it's own set of problems too)
Yes, the splice should be re-made every 3-5 years, clipping a few links. Maintenance.

If the splice is jamming or giving trouble, you are using the wrong splice. An irony splice will fly down the hole without pausing the windlass. That is what I use with a windlass. It is still full strength (I've pull tested them, so did Brian).

All credit goes to the late Brian Toss.




Sail Delmarva: The Best Rope-to Chain Splice
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Old 26-07-2020, 12:42   #33
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Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?

Quote:
Originally Posted by MicHughV View Post
to me the issue is kinda moot.

in any anchorage you are likely to get a dozen or more boats...different lengths, different hulls, different skippers, etc, ad infinitum.

no two boats are likely to have the same anchorage system, be it rope, chain or any combo of the above, and anchor types can run from one extreme to another and each skipper is likely to deploy what has worked best for him, be he a pro or a newbie, using one anchor or two, etc, etc. On the far end of the scale, bottom holding is a topic all of it's own.

some will use 10:1 scope others 5:1, etc, etc.

some boats swing to an anchor and some are rock steady.

there is simply not a one size fits all here...

I know what works best for me and it's the same system I've used on different boats over 40 years and no amount of discussion, modeling, formula's, theories, or otherwise is likely to have me change anything.

I don't think I'm alone in this view.
Virtually all long distance cruising boats, worldwide use all chain for normal scopes. Exceptions are not common. I photographed all boat anchors within snorkeling distance for well over a year and only remember one boat that did not have all chain as their primary rode.

I agree the scopes selected by other skippers does vary considerably, and is sometimes not appropriate.

Having good oversized anchoring gear is a significant help managing this problem. If a neighbour uses as abnormally short scope you can match this if necessary knowing they will drag first. If they use an abnormally long scope your oversized anchoring gear allows the safe use of of shorter scopes if necessary to stay out of their large swing circle.
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Old 26-07-2020, 12:47   #34
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Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?

Never seen that splice. Mine is not a rope/chain gypsy. Mine is chain only. Can a rope/chain gypsy damage nylon line?
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Old 31-07-2020, 08:47   #35
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Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?

My five (two? one? not sure about the use of that idiom) cents on the matter. Five meters of chain (about 15 feet) and 50 meters (150 feet) of rope/line (ankarolina, flat anchoring ribbon), is what we usually use here in the Baltic, is plenty enough for almost any situation. I have a Vega, she's about 2.5 tons loaded, and I use a 7.5kg Bruce. I'll upgrade to 10kg just in case when I install a bow roller. I also have 40 meters of actual polyester anchor rope, with the first 15 meters being weighted with lead, but I have yet to use it.
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Old 31-07-2020, 10:56   #36
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Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?

I'm struggling with this.. new owner of a Sabre 28. It came with a danforth anchor weighs about 15-20lb and 6ft of chain connected to a lot of rope. No Windlass
for weekend Bay sailing what is my best solution?
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Old 31-07-2020, 16:25   #37
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Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?

Our 43' express cruiser uses a 44 lb Bruce, a swivel, then 25' of BBB 5/16 and 200' of 9/16 nylon. The Bruce lacks holding in soft mud and once had difficulty penetrating hard sand. Diving down the 15' revealed a bottom consistency not unlike a sidewalk. The next time there, I had used an angle grinder to sharpen the edges of the Bruce (not shaving sharp, more like a butter knife) which allowed it to penetrate in about 1-2 anchor lengths. As to the chain, since it's a powerboat with a mid 20s cruise speed, it's sensitive to weight so having 200 - 250' of chain isn't practical. Our 25' of chain, which some would say is inadequate, has been sufficient to prevent dragging in several storms. After one nasty unexpected 2 am storm, the anchor was discovered the next morning to have buried itself with the top of it over a foot below the bottom surface of gravely sand. Dragging? Maybe another anchor length or two while burying itself. It was difficult to retrieve but it held, with only 25' of chain.
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Old 01-08-2020, 19:21   #38
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Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?

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Originally Posted by MathiasW View Post
We have had a very long thread on anchoring ...where my mathematical / physical model of anchor chain and snubber/bridle was most thoroughly discussed.

.....Have a look at the curve attached. It is the elasticity of the chain - defined as derivative of the chain's potential energy with regards to wind force, and plotted as a function of scope, i.e. chain length L divided by anchor depth Y. ....
Comments are most welcome!
Mathias, I am still having a very hard time wrapping my head around the graph attached to your post, and to previous posts. The ordinate is the % "stretch" of the chain, and the abscissa is proportional to the square root of the horizontal force at the anchor due to wind (or whatever) plus a constant Y, the depth. If the equation is to be dimensionally consistent, Y must be dimensionless as it is added to a, a dimensionless force. How is Y non-dimensionalized?

Thanks for your patience, Richard
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Old 02-08-2020, 07:28   #39
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Re: How Much Chain, Really... In Non-Rock and Non-Coral Areas?

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Mathias, I am still having a very hard time wrapping my head around the graph attached to your post, and to previous posts. The ordinate is the % "stretch" of the chain, and the abscissa is proportional to the square root of the horizontal force at the anchor due to wind (or whatever) plus a constant Y, the depth. If the equation is to be dimensionally consistent, Y must be dimensionless as it is added to a, a dimensionless force. How is Y non-dimensionalized?

Thanks for your patience, Richard
Hi Richard, no problem at all. The information I had shared was quite condensed. Perhaps too much so. The abscissa of that graph is not what you say, but rather the ratio of chain length L to anchor depth Y, so scope, and thus is dimensionless. Other abscissa parameters such as a/Y are possible as well here. When I choose a/Y, then this again is dimensionless, since the parameter a of the catenary has units of length. Remember that the catenary equation I am using is y = a (cosh(x/a) - 1).

As to the ordinate, here I used the trick to normalise the graph by dividing the curve by its maximum, and then expressing the result as percentage of this maximum, so I multiplied it by a factor 100. Consequently, at the peak of the graph, it will touch 100%, by definition. And because of this division, the result is also dimensionless. But it is still the elasticity of the the chain, just as a percentage of its maximally possible elasticity at this given anchor depth Y.

The main motivation for expressing it as a percentage of the maximum was to show as clearly as possible where the chain works well, and where it does not.

Now, the proportionality of the elasticity with the anchor depth Y is not obvious in this graph, I am afraid. For this one has to go back to the original equation. This would be equation 21 in my long German paper, version 22, where you can see that the elasticity, i.e., derivative of the chain's potential energy with respect to the wind force F, is a product of the anchor depth Y times a complicated function which, however, only depends on the scope L/Y.

This overall proportionality with Y gets obviously 'cut out' when I normalise the graph to its maximum value, and so I had to mention it as a side note.

Hope this explanation helps.

The long German version as well as other material can be found at

https://trimaran-san.de/die-kettenku...atiker-ankert/


Best

Mathias
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