Anchor chain and rode

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Brian D

Brian D

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Feb 17, 2006
5,274
Lancer 27PS MCB Camp Pendleton KF6BL
So, do you measure the scope from the tip of the anchor or from the splice of the chain and rode? I will be marking my rode in a few weeks and I thought about measuring the marks from the splice. Guess it dose not make a difference. If measured from the splice, one will just have more scope.

How do you measure your scope?
 
B

BarryL, 1986 O'day 35

scope

Hello,

You measure scope from the ANCHOR, not the rode, to the ANCHOR ROLLER on deck. Some people have 5' of chain, others have 50' of chain, others have ALL CHAIN.

If you are anchored in an area with significant tides, and you will be there for at least one tide cycle, be sure to use the high tide depth for your scope calculation. For example, if I anchor in 10' of water at low tide, and I want 5:1 scope, and my anchor roller is 3' off the water, I need to have (10 + 3) X 5 = 65' of rode out. If I will be there at high tide, and the tidal range is 5', I really need (10 + 3 + 5) X 5 = about 90' of rode.

Barry
 
R

Ross

Brian D, It is all rode.

Just be generous with your measuring stick.
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,759
Canadian Sailcraft 36T Casco Bay, ME
Some people start measuring...

Scope at the rope/chain intersection. This way if you let out 7:1 and forget to add bow height that extra 30 feet of chain you did not count will still likely give you a 7:1.

I think it's just much simpler to take your max water depth (max tide depth) and add 3 or 4 feet of bow height and measure from the anchor..

I count my rodes scope from the anchor including the chain..
 
R

Ross

Brian D, For me I just try to err on the side of more is better

The concept of scope has to do with the angle of pull on the anchor. If you just drop the anchor until it touches bottom the scope is 1:1 and all pull is going to tend to raise the hook. At 7:1 the numbers become 1/7=.14 which means that 86 per cent of the pull on the rode will be horizontal and 14 percent vertical. Thus as the anchor tries to dig in because of its shape the rode also tries to pull it up. At 10:1 scope 90 percent of the pull on the rode is horizontal and only 10 per cent is vertical. In the other direction at 3:1 scope 33 per cent is vertical and only 66 percent is horizontal.
 
J

Joe

ross.....

can your simple formula be affected by adding more chain to the rode, or deploying a kellet?
 
S

sailortonyb Allied Mistress 39

Joe

I'm not much for adding links on here but this one should answer your question.
You still need a certain amount of scope because you still need as close to a horizontal angle as possible. The additional chain and a kellet help quite a bit. I now use a lot of chain, but I still use a 7 or 8 to one scope under normal conditions. If water is shallow, I use around 10 to one only because it's not much rope/chain.
I never used a kellet, but I should.

Tony B
 
R

Ross

The numbers I used were for a bar taut rode

adding chain or using heavier chain will reduce the angles and increase the effective holding. I have read that twenty pounds more chain is better than twenty pounds of kellet. I use a 3/8 chain for the weight. 5/16 would be strong enough.
 
W

Warren Milberg

Scope

I have always thought of scope simply as the ratio of the distance from your bow directly to the bottom times whatever factor you think necessary for proper holding power of your anchor. If, for example, you are in water that is 7 feet deep and it's 3 feet from your bow to the water and you want a scope of 7:1, you let out 70 feet of anchor, chain, nylon or whatever your ground tackle is composed of.... Whether you measure from one end of the anchor or the other is insignificant.
 
B

Brian D

It probably is insignificant

But my thoughts are simply if one has 30' of chain and 70' or line, then one has 100' of everything and in 10' water that meets the 10:1 scope. However, if one measures only the line, then one is using 7:1 scope. I guess that would be true if the chain was embedded in the ocean floor.

OK... I do understand the scope theory and the water depth + bow height concept. I was just curious to know where does everyone start their measurements. Anchor tip or rope/chain splice. Not that it matters, just a discussion.
 
J

jviss

Huh?

I don't get the question - why do you ask "Anchor tip or rope/chain splice" when the obvious answer is neither? The obvious answer is the rode is the line and chain connected to the anchor. The length would be the length of the chain plus the length of the rope. What does the "tip of the anchor" have to do with this? Why make is so obtuse?

Scope is defined variously, most commonly rode to depth of water, or rode to depth plus height of roller/anchor rode attachment point.
 
C

Cap't Ron

Catenary

Brian, it sounds like you need to learn the meaning of this word, look it up.

Anchoring is hard to learn from a book, you need to drag a few times soooo bee shore ya got swinging room 360 and measure the maximum of your scope from shackle on your anchor to snubber near the roller, and do NOT anchor in a depth that you do not have enough scope for proper catenary.

Best to have ALL CHAIN always, always and always...will keep ya in shape too lol
 
S

sailortonyb Allied Mistress 39

Warren and Brian

Warren, you are correct. Your rode is measured from the anchor atachment point to the bow roller or whatever. Rode includes both chain and rope. It is the total combined length.
Scope is the ratio of the rode to the depth of water plus the height of the point at which the rode contacts the boat, which is usually a bow roller. but not always.

Brian: I hope that anseres your question.

Tony B
 
J

Joe

Tony B..............

Thanks for that link... I'm hoping that everyone takes the time to read that article. Submitting authoritive information on something as important as anchoring is much appreciated.
 
C

Craig Smith / Rocna Anchors

Try these

for more reading:

http://www.petersmith.net.nz/boat-anchors/catenary.php

http://www.petersmith.net.nz/boat-anchors/kellets.php
 
C

Craig Smith / Rocna Anchors

And, re kellets:

http://www.petersmith.net..nz/boat-anchors/kellets.php
 
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