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Old 29-01-2012, 06:53   #1
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Anchor Chain Length Versus Weight

I am looking at replacing the ground tackle on my recently acquired Com-Pac 35 and am considering going from 3/8" chain to 5/16". At present, only about 100' of 3/8" fits comfortably on its side of the chain locker. I don't feel 100' of chain is enough if i am lucky enough to get to the Virgin Islands and beyond. 3/8" weighs about 1.7 lb/ft and 5/16" G4 weighs about 1.0 lb/ft. First question is, how much chain should I carry and the second is would the lesser weight of 5/16" chain be at all a disadvantage?
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Old 29-01-2012, 06:59   #2
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Re: Anchor Chain Length Versus Weight

I had 150' of 5/16" G4 backed by 175' of 5.8" three strand nylon rode, and sometimes used all 150 feet of it, but never had to run out any of the nylon during our two years cruising the West Indies. Our boat weight about 12.5 tons. I don't think you'd find that the difference in the weight of the chain will make any difference whatsoever if you go with 150' or more of the 5/16".
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Old 29-01-2012, 07:00   #3
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pirate Re: Anchor Chain Length Versus Weight

Personally.... the deepest I'm prepared to anchor + 7xlength of boat minimum...
But others Will disagree....
As to chain size... will the smaller fit your windlass okay..??
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Old 29-01-2012, 07:06   #4
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Re: Anchor Chain Length Versus Weight

5/16" g40 is more than enough strength for a 35 foot boat. It is 1.1 lb per foot.

If I were you I'd go with about 100 ft of that backed with 200 ft of 5/8 nylon brait. Brait falls much more compact into the locker and that should give you enough chain out to handle bottom abrasion and keep your nylon off the bottom.

(edited chain size)
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Old 29-01-2012, 07:12   #5
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Re: Anchor Chain Length Versus Weight

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Originally Posted by boatman61 View Post
Personally.... the deepest I'm prepared to anchor + 7xlength of boat minimum...
But others Will disagree....
As to chain size... will the smaller fit your windlass okay..??
What does boat length have to do with the depth you would choose to anchor? I don't understand the reasoning.
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Old 29-01-2012, 07:15   #6
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Re: Anchor Chain Length Versus Weight

I think all of the above is good advice.

Weight of a chain rode is 90% a minus, according to what most people think today. It is a plus only when it makes shock-absorbing catenary in less than difficult conditions. Otherwise it doesn't help you, and hurts the trim of your boat.

Substituting a larger size and weaker grade of chain with a smaller size and stronger grade of chain is usually considered a good move.

I especially like Hud's suggestion of 150' of chain with a bunch of rope behind it "just in case". I don't know what your draft is, but 150' of rode in a boat that size in waters which don't have huge tides ought to be enough for 90% of all the conditions you will encounter.

By contrast, I have 330' of 1/2" chain, and put it all out fairly often. BUT -- I have nearly 8' of draft, and in my sailing area there are places with nearly 50' tides. In your case, I would go with something like Hud's setup.

Good luck and please be sure to let us know what you end up doing, and how it works out for you.
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Old 29-01-2012, 07:20   #7
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Re: Anchor Chain Length Versus Weight

50' tides - WOW! Really, where?
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Old 29-01-2012, 07:22   #8
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Re: Anchor Chain Length Versus Weight

Quote:
Originally Posted by Don Lucas View Post
50' tides - WOW! Really, where?
Bay of Saint Malo -- highest tides in the world except in one spot in Newfoundland.

It is pretty wild sailing there. 10 knots currents in some places.
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Old 29-01-2012, 07:44   #9
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Re: Anchor Chain Length Versus Weight

150 feet of either will do the job in the Eastern Caribbean.

For equal lengths of chain, the heavier chain will improve holding and reduce swinging in all conditions, in spite of what your intuition and the opinions on the Internet tell you. I have yet to see a solid analysis posted -- everyone that tries makes too many simplifying assumptions -- an accurate analysis is complex, and it probably wouldn't persuade too many people anyway. To grasp this, you have to be able to visualize resolving the vector analysis of the chain tension into horizontal and vertical components as you move from one end of the chain to the other. You can't just analyze what happens at the bow of the boat and get an understanding of what happens at the anchor.

Empirically, most folks that we run into who have tried heavier chain won't go back to the lighter stuff, assuming their boats can handle the weight in the bow, which is a problem for light displacement boats.

Strength of the chain is rarely an issue, given equal quality, between 3/8" and 5/16".
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Old 29-01-2012, 07:47   #10
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pirate Re: Anchor Chain Length Versus Weight

Quote:
Originally Posted by SailFastTri View Post
What does boat length have to do with the depth you would choose to anchor? I don't understand the reasoning.
What Dockhead said.... if your in a tidal region you also have to allow for depth at H & Lwater................ 100ft on the deck at L=50ft at high in some places....
UK, France etc...
On the rope I disagree... on my secondary yes..
But my main is all chain...
Horse's for course's...
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Old 29-01-2012, 07:51   #11
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Re: Anchor Chain Length Versus Weight

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Originally Posted by boatman61 View Post
What Dockhead said.... if your in a tidal region you also have to allow for depth at H & Lwater................ 100ft on the deck at L=50ft at high in some places....
UK, France etc...
On the rope I disagree... on my secondary yes..
But my main is all chain...
Horse's for course's...
What you wrote has nothing to do with boat length.
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Old 29-01-2012, 07:51   #12
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Re: Anchor Chain Length Versus Weight

Quote:
Originally Posted by Play Actor View Post
150 feet of either will do the job in the Eastern Caribbean.

For equal lengths of chain, the heavier chain will improve holding and reduce swinging in all conditions, in spite of what your intuition and the opinions on the Internet tell you. I have yet to see a solid analysis posted -- everyone that tries makes too many simplifying assumptions -- an accurate analysis is complex, and it probably wouldn't persuade too many people anyway. To grasp this, you have to be able to visualize resolving the vector analysis of the chain tension into horizontal and vertical components as you move from one end of the chain to the other. You can't just analyze what happens at the bow of the boat and get an understanding of what happens at the anchor.

Empirically, most folks that we run into who have tried heavier chain won't go back to the lighter stuff, assuming their boats can handle the weight in the bow, which is a problem for light displacement boats.

Strength of the chain is rarely an issue, given equal quality, between 3/8" and 5/16".
Well, I think everyone would agree that heavier chain will give you more comfort at anchor. The catenary dampens the motion of the boat.

But I don't think that any complex calculations are required to demonstrate that heavy chain can't significantly improve the ultimate holding of your anchor. Once the catenary is pulled out of it, it behaves just like any other anchor rode which hasn't broken yet. Catenary ceases to change the angle of pull relative to the seabed, once the chain is pulled out straight.

So I think it is pretty hard to argue with the proposition that for ultimate holding, at least, you are better off putting the extra weight into the anchor, and taking it out of the chain.
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Old 29-01-2012, 08:00   #13
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Re: Anchor Chain Length Versus Weight

I would agree that 150 feet of the 5/16 should be fine. In the western Caribbean it is pretty rare to anchor in more than 20-30 feet of water, but there are places where you'll be in 40-50 feet and there will be coral around, so more chain can be useful. Obviously none of us deliberately anchor on live coral, but many anchorages in the western Caribbean have lots of chunks of dead coral strewn about the bottom making longer lengths of chain desirable. Also, there are places in the San Blas where the swinging room is limited, the water is deep, and therefore you need to be on short scope and/or two or more anchors just to keep your boat in the deep water.
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Old 29-01-2012, 08:01   #14
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Re: Anchor Chain Length Versus Weight

Quote:
Originally Posted by SailFastTri View Post
What does boat length have to do with the depth you would choose to anchor? I don't understand the reasoning.
I don't think 7 x boat length is much of a restriction as 7 times 35 foot boat is 245 feet of depth. Few folks anchor in 245 feet of water or more.

Maybe he meant to say chain/rode length can be calculated at 7 times boat length. So 240 ft of chain on a 35 footer would about the maximum.

But anyway, as others have stated 3/8" chain is rather extreme overkill on a 35 ft boat. I would suggest 5/16" is "heavy" and 1/4" is okay but "light".

Maximum rode/chain length is a variable based on your normal anchoring areas. If you only cruise and anchor in shallow/shoal water areas, a 100 feet would be fine. But if you do deep anchorage like the Caribbean where average anchorages are 40 ft (+/- 20 feet) then 200 feet of chain would be better.

But for a small light boat a combination of chain/nylon rode would be best as suggested by Hud3. Plenty of chain for deep and sharp coral areas and extra length available with the nylon for high wind situations.
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Old 29-01-2012, 08:14   #15
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Re: Anchor Chain Length Versus Weight

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Originally Posted by Dockhead View Post
So I think it is pretty hard to argue with the proposition that for ultimate holding, at least, you are better off putting the extra weight into the anchor, and taking it out of the chain.

+1
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