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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #1  
Old 08-01-2007
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Anchor rode question

I know that when anchoring it is good practice to let out 7:1 to 10:1 rode length. I just picked up a new anchor for my 25' boat with 15 feet of chain and 200 feet of nylon line. Now when I let out my 7:1 do I count the 15' of chain in that or is it 7:1 from the nylon line?

Ex. 7:1 in 5 feet of water - Do I let out the 15' of chain and then 20' of line for a total of 35' of rode?

or

Do I let out the 15' of chain and then 35' feet of the nylon line?

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Old 08-01-2007
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Umm... the 15' of chain count as part of the scope of rode let out... but don't forget to include the maximum depth of water based on high tide and also add the distance from the waterline to the bow roller.

For instance, say you're anchored in 10' of water, but it is low tide, and high tide is 18' of water. If you anchor out with a scope of 7:1 for the 10' and let out 70' of rode, 55' of rope and 15' of chain, at high tide you'll be at 3.88:1 scope... and if you've got three feet of freeboard between your bow roller and the water, then the scope of 70' only is at 5.38:1 at low tide and 3.33:1 at high tide... hmm... not exactly what you'd want.

You'd need to let out 147' of rode to get a true 7:1 scope.

In your example of anchoring in five feet of water—assuming you have three feet of freeboard, as in my previous example—you'd actually have to let out 56' of rode—15' of chain and 41' of rope, to account for the actual depth plus height to bowroller. This also assumes that there is either no tide or that five feet is the high-tide water depth.
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Last edited by sailingdog; 08-01-2007 at 10:43 PM.
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Old 08-01-2007
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What Sailingdog said, plus... 7:1 and 10:1 are pretty big scopes. With a mostly rope rode like you have, I'd probably set 5:1 most times and 7:1 for an overnight. If there are other boats around you when you anchor, and you see mostly chain off their bow or windlass, expect anywhere from 3:1 (lunch) or 5:1 (overnight). I'll do 7:1 or higher for excessively high winds (25+) or storms. If you put out too much scope and are in an anchorage with others, there's a possibility you'll swing into them as you come around during wind shifts.
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Old 08-02-2007
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What they said ^

If you want to risk getting confused with more info, check out this article:
www.rocna.com/boat-anchors/catenary.php

Our User's Guide has general stuff in it too that may be of interest. Find it under "printable info" on our website.
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Old 08-02-2007
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BTW, some anchors require more scope than others... I've found that 5:1 is generally plenty, with 30' of 5/16" G4 High-test chain and 5/8" nylon three strand as the main rode. Of course, I do have the advantage of being able to anchor in waters that many could not, having a shallower draft than most.
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Old 08-02-2007
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When in doubt........
Let it out.

Just make sure your not going to ride into or over sombody else.
If you have plenty of room and no other boats in the vicinity, you can't go wrong with letting more out.
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Old 08-02-2007
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Also, please remember that the first person in an anchorage has their pick, and if you arrive later, you have to accommodate the choices they made, since they were there first. If you arrive first, don't let out 10:1 scope unless you really are expecting a big blow to come along shortly... since you'll screw up much of the anchorage for people who arrive later.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
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—Cpt. Mal Reynolds, Serenity (edited)

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thanks for all the responses...anchoring is just one of those things that always makes me nervous when staying overnight and when it gets rough out. I like to have the peace of mind to know I set the anchor correctly and let out the proper amount of rode with all of the factors taken into consideration
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Old 08-02-2007
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Keep worrying about it, the nervousness is good for keeping you from sleeping too heavily. ;-) I like to wake up once or twice in the middle of the night and check on things when at anchor. At the very least pop my head out of the hatch and make sure the last visual marker I recall is still in roughly the same spot.
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If you're not waking up every couple hours when on the hook, you're probably taking something for granted... and that will generally come back to bite you where the sun don't shine one time or another.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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