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-   -   Reduction in anchor scope with chain use (http://www.sailnet.com/forums/general-discussion-sailing-related/93168-reduction-anchor-scope-chain-use.html)

sailak 10-17-2012 01:36 AM

Reduction in anchor scope with chain use
 
Tonight in our Coast Guard Boating Safety course the instructor gave a "rule of thumb" that 1 foot of chain equals 10 feet of line.

His example was anchoring in 50' with a scope of 7 to 1 you would need 350' of line. But if you had 25' of chain (equal to 250' of line according to his rule of thumb) you would only need 50' of line -- 75' total rode.

I'm new to boating but have never heard this rule of thumb. I agree that chain can reduce the amount of rode needed to safely anchor but have to wonder if the advantage is as great as he is saying.

Anyone heard of this?

Stumble 10-17-2012 01:57 AM

Re: Reduction in anchor scope with chain use
 
That may be the stupidest thing I have ever heard.

Chain can reduce the amount of rhode needed in mild weather, but you still need at least 3:1, preferably 5:1. For storm conditions 10:1 is recommended in both chain and line.

bristol299bob 10-17-2012 02:01 AM

Re: Reduction in anchor scope with chain use
 
no, of course that is not right. by that logic, anchoring 5:1 in 50' of water requires only 25 ft of chain. Chain gives you lots of benefits but warping space time is not one of them :-)

I measure chain and line the same, and sleep well at night.

Geoff54 10-17-2012 02:10 AM

Re: Reduction in anchor scope with chain use
 
The rule of thumb that I remember is that chain is about 10 times the weight of nylon but that example makes no sense.

My rule of thumb is all chain, minimum 5:1, extra long nylon snubber, sleep well.

blt2ski 10-17-2012 02:21 AM

Re: Reduction in anchor scope with chain use
 
So this guy is saying 1.5-1 ratio?!?!?! The "ONLY" time I have seen this ratio is for a permanent anchor point. And one is using usually all chain, plus and anchor/wad of wt at the bottom that is multitudes more than one would use normally. IE 350-500 lbs of anchor vs 25-50 lbs. So the scope, while important, not as important as it would be in normal anchoring situations.

I personally want at least 2 if not 3-1 minimum.

Marty

delite 10-17-2012 03:01 AM

Re: Reduction in anchor scope with chain use
 
Call the instructor out on that one. I cant imagine anyone anchoring in 50ft of water with only 75 ft of chain out. Likewise unless there is a storm most people dont have 7:1 scope, especially in a crowded bay.

chef2sail 10-17-2012 03:18 AM

Re: Reduction in anchor scope with chain use
 
Make him show you where he got this information or guidence when the minimum I have alwasy seen is 5:1

Mike Banks 10-17-2012 03:19 AM

Re: Reduction in anchor scope with chain use
 
There is only the rule of common sense. The weight of chain rather than length is important--but in deep water you have to use nylon or you will simply not be able to recover all the chain if it is heavy short link chain--which is the best to buy.

If you have such chain, you need to put out as much as you can in the circumstances. I know that is stating the obvious, but after reading the first post the obvious seems to have been overlooked. The comparison in weight of chain and nylon is completely irrelevant. The weight of chain is relevant--because you need to ensure you put out no more than your winch can handle in a vertical lift plus the force necessary to pull the pick out of the mud plus the weight of said pick and an angel of you use one. If you put out more than that you will be unable to get it back. If you regularly set anchors in deep water fifty feet of heavy short link chain with an angel of about twenty pounds set in the chain about ten feet from the rode end, then a five-to one scope to the end of the chain with the angel fitted is a minimum and ten is better. What pulls out the anchor is the weight of the boat and the speed it builds up as it surges backwards between waves in a storm, because when the chain pulls taut this is transferred to the ground tackle. An angel plus chain softens this and the elasticity of a 20mm nylon rode softens it still further. Even so--such an anchor can still drag--sometimes anchors land on sea beds where they will not grip. In such a situation, if the water is shallow, say twenty feet or so--the more chain you can let out the better.

My boat weight five tons, and with stores and fuel more than six when cruising. My anchor is sixty pounds and I use at least thirty metres of 13mm short link chain, to which is lock-spliced one hundred metres of 20mm hard woven nylon rode. Even so, I would hate to have to ride out a storm at anchor. I am just experienced and pessimistic enough to realise that if I am wearing cast-iron pants, fate does not often try to kick my arse.

Maine Sail 10-17-2012 07:12 AM

Re: Reduction in anchor scope with chain use
 
Quote:

Originally Posted by sailak (Post 934672)
Tonight in our Coast Guard Boating Safety course the instructor gave a "rule of thumb" that 1 foot of chain equals 10 feet of line.

His example was anchoring in 50' with a scope of 7 to 1 you would need 350' of line. But if you had 25' of chain (equal to 250' of line according to his rule of thumb) you would only need 50' of line -- 75' total rode.

I'm new to boating but have never heard this rule of thumb. I agree that chain can reduce the amount of rode needed to safely anchor but have to wonder if the advantage is as great as he is saying.

Anyone heard of this?

Sounds like this guy should be TAKING not teaching this class.....:eek:

chucklesR 10-17-2012 08:49 AM

Re: Reduction in anchor scope with chain use
 
So in ten feet of water I can toss out 10 feet of chain and call it the same as 100 foot of rode.

Stupid. The rule of thumb is chain weighs 1 pound per foot (3/8) and rope (5/8) weighs 1 pound per ten foot. That has nothing to do with anchor rode or scope.

Seems he has his thumb in the wrong place.

Scope is about angle of pull on the anchor, the less the better. Heck to pull a anchor up you shorten scope!

I wouldn't even use his ratio for a mooring ball, lunch hook, or to prevent drift while fishing.


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