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Old 06-10-2019, 08:34   #16
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Re: Cruising Anchor Chain Length

We started in The Philippines(+10yrs), spent time all around Asia, then 3+years in the Medd, and now in the Caribb. We carry 100m of chain. And while we've seldom used more than 70m (usually 30m-40m, give or take), and have only slipped a couple of times. I would not carry less than 100m unless I was only sailing locally and knew the depth/bottom. And even though we use a 25kgm Rocna (a little oversized) we always use a 5:1 scope, or more if the wx requires it. FWIW
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Old 06-10-2019, 08:39   #17
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Re: Cruising Anchor Chain Length

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3 to 1 is crazy except for a lunch hook in a tight anchorage type of thing, although in a perfect substrate with a large enough anchor it will work fine, but how do you know your set perfectly and the anchor hasn’t found hard bottom just under the sand?
Read some of the material from Steve Dashew it may make you change your perspective in what you consider is short scope. He is much more game than I am when accepting small amounts of chain. He uses a very large 110kg Rocna, which helps especially on a narrow beamed and relatively low windage 64 foot power boat, but does not give the anchor an easy time:

SetSail FPB » Blog Archive » More on Anchors and Sizing:

“We are surrounded by a lot of 40- to 50-foot (12- to 15-meter) yachts. The water is 55 feet (17m) deep at half tide. We set our big ROCNA anchor on 2.5-1 scope, and then, with a firm bite established, shortened the chain rode to 100 feet (30m). A scope of 1.6-1. If you calculate the angle off the bottom, combine the chain length with Wind Horse’s length, we need about 150 feet (45m) of swinging room.
Compare this to a 40-foot (12m) yacht anchored with a normal sized anchor. They will need at least 4-1 and probably 5-1 scope. Take their length and add it to 240 feet (74m) of chain, allow for angles, and you have a swinging radius of 220 feet (67m) at a minimum. The smaller boat with its normal (undersized by our standards) anchor takes a lot more room than the bigger boat with an oversized anchor. Is there a lesson here?
Not only does this work in crowded anchorages, but it benefits you in secluded spots which might otherwise be too tight with a normal anchor.
The anchor, regardless of design, will set faster, being bigger. This means it drags less before it digs in. That reduces the risk of it fouling debris. And since you take less swinging room, the chain sweeps a much smaller area of the bottom as the boat changes position, again reducing the risk of fouling.”
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Old 06-10-2019, 08:52   #18
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Re: Cruising Anchor Chain Length

Where we are, Caribbean windwards and Leewards, there is often very good holding in pretty shallow water. 54 kilo Rocna, all 10 mm chain, 40 ton boat, 57 feet. We rattle off 3:1 and back down. It sets most times so hard chain is ripped off overpowering the clutch.
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Old 06-10-2019, 09:00   #19
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Re: Cruising Anchor Chain Length

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Originally Posted by noelex 77 View Post
Read some of the material from Steve Dashew it may make you change your perspective in what you consider is short scope. He is much more game than I am when accepting small amounts of chain. He uses a very large 110kg Rocna, which helps especially on a narrow beamed and relatively low windage 64 foot power boat, but does not give the anchor an easy time:

SetSail FPB » Blog Archive » More on Anchors and Sizing:

“We are surrounded by a lot of 40- to 50-foot (12- to 15-meter) yachts. The water is 55 feet (17m) deep at half tide. We set our big ROCNA anchor on 2.5-1 scope, and then, with a firm bite established, shortened the chain rode to 100 feet (30m). A scope of 1.6-1. If you calculate the angle off the bottom, combine the chain length with Wind Horse’s length, we need about 150 feet (45m) of swinging room.
Compare this to a 40-foot (12m) yacht anchored with a normal sized anchor. They will need at least 4-1 and probably 5-1 scope. Take their length and add it to 240 feet (74m) of chain, allow for angles, and you have a swinging radius of 220 feet (67m) at a minimum. The smaller boat with its normal (undersized by our standards) anchor takes a lot more room than the bigger boat with an oversized anchor. Is there a lesson here?
Not only does this work in crowded anchorages, but it benefits you in secluded spots which might otherwise be too tight with a normal anchor.
The anchor, regardless of design, will set faster, being bigger. This means it drags less before it digs in. That reduces the risk of it fouling debris. And since you take less swinging room, the chain sweeps a much smaller area of the bottom as the boat changes position, again reducing the risk of fouling.”
Dashew raises a good point. Indeed the size and holding power of the anchor is key, whereas angle of pull is a secondary factor that with lowered angle can assist in keeping the anchor's full holding capacity.

But there is a significant issue with Dashew's approach in a crowded anchorage if one is the only boat using a short rode length and thus having a smaller rotational radius than the other boats that are close by because you set your self up to become a problem boat when the wind or tide shifts and all the boat swing around their anchor pivot point. Experience has taught me that one does not want to be an outlier as to the amount of rode deployed in crowded anchorage conditions; one does not want to be too short or too long relative to the other boats.

I love the post about using consensus and anchoring in the same sentence.

The added weight of chain and its catenary effect is modest which is why the use of kelts is also of limited benefit; there is a degree of helpfulness in moderate winds and tides to the additional weight of iron on rode but the better use of added weight [and sizing] would be in utilizing a moderately larger anchor versus using a heavier grade of chain of comparable strength.
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Old 06-10-2019, 09:13   #20
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Re: Cruising Anchor Chain Length

Dont forget to factor in your windless abilities, or your own should it fail.
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Old 06-10-2019, 09:17   #21
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Re: Cruising Anchor Chain Length

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Here is a photo of a boat with a Rocna and an all chain rode in about 25 knots of wind (higher in the gusts). You can see the chain is essentially straight in the gusts with no beneficial catenary:

I can’t find the data for depth, scope and wind speed in the gusts when the chain was pulled taut. I never felt like my 60’ of chain (attached to 40’ of line) was pulled completely off the bottom in 25 knots of wind. That was at a scope of 5-1. https://youtu.be/w4qO_dIegaM
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Old 06-10-2019, 10:16   #22
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Re: Cruising Anchor Chain Length

Like almost everything else in boating, one size does not fit all conditions. If you change your cruising grounds, could you simply not be prepared to modify your gear? I did when I moved from No. California to BC. It's deeper here with larger tidal ranges!
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Old 06-10-2019, 10:23   #23
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Re: Cruising Anchor Chain Length

We carried 70m/230' of 3/8" high test chain on a 20,000# boat with a 45# CQR in French Polynesia and only used the full length once. That was a forecast tropical depression with 50 mph plus winds. We were in 30' feet of water and let out the entire length just because we could. Always used a 30' 5/8" three strand nylon snubber.

The problem with rope rode is abrasion where it passes through chocks on the boat. Stretch under a heavy load will pull the line past the chafing gear leaving the line unprotected. From experience it is no fun trying to add chafing gear to a line where it passes through a chock in 40k winds. If you chose to slowly pay out rode to vary the chafe point be very careful. In high winds the force on the line is tremendous and it can get away from you.
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Old 06-10-2019, 11:09   #24
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Re: Cruising Anchor Chain Length

When I upgrade our ground tackle I went BIG. Ditched the 16kg Delta that came with the boat, which I felt was undersized, and the 50m of ungraded 8mm I swapped out to a 33kg Rocna Vulcan teamed with 60m of 8m G70 spliced to 40m of 16mm Octoplait.

Thinking is why bugger about in a gale/storm trying to set a secondary anchor when you can have your primary anchor rated to hold and set just one. Yes I do have a secondary anchor but no I've never had to dig it out the cockpit locker (yet!).

60m of chain at 4:1 is 13.5m of water (add the bow roller height to your calculations on scope, the pivot point isn't water line) or 5:1 in 10m of water, which is fairly common in the Adriatic and Ionian where we cruise. The size and design of the Vulcan means we can anchor safely at 3:1 and have done so in up to 25kt winds. It also means we don't have to drop as much chain in harbour meaning less chance of snagging other chains.

The 40m of 16mm Octoplait is there for the rare occasions we anchor in deeper water or for extending scope out to 7 or even 10:1 for serious blows. That said we did end up dropping 85m to reverse into harbour the other day just because the wind was off the beam and we slightly misjudged the distance to the wall

There's no ideal set up but going one (or 2) sizes up on the anchor and taking as much chain as you can will serve you better in the long run. If you are worried about weight up front you can always move weight back aft to compensate. If it helps 8mm G70 is stronger than 10mm G30 and weighs significantly less per m.

Hope that helps
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Old 06-10-2019, 16:42   #25
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Re: Cruising Anchor Chain Length

If more chain becomes a weight issue in the chain-locker, give up a few cases of beer and purchase Stainless Steel 316 Chain which weighs considerably less than Hot Dipped Galvanised Chain and another Plus is that SS 316 chain is far superior in breaking strength. Cost is the only real issue, but as I already pointed out, give up a few cases of beer for the security of SS 316 CHAIN.

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Old 06-10-2019, 17:49   #26
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Re: Cruising Anchor Chain Length

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If more chain becomes a weight issue in the chain-locker, give up a few cases of beer and purchase Stainless Steel 316 Chain which weighs considerably less than Hot Dipped Galvanised Chain and another Plus is that SS 316 chain is far superior in breaking strength. Cost is the only real issue, but as I already pointed out, give up a few cases of beer for the security of SS 316 CHAIN.

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Sorry, but both of your premises are incorrect: The density of 316 s/s and the typical carbon steel of galvo chain are virtually identical, and 316 has considerably less tensile strength than the carbon steel.

And the real issue is neither weight nor strength of the 316 chain, but the unpredictable behavior of 316 under water and with cycling loads.

There are some vendors of 2205 duplex stainless chain I believe, and that would meet your criteria of greater strength and reduce the odds for crevice corrosion failure. Price and availability are an issue...

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Old 06-10-2019, 17:54   #27
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Re: Cruising Anchor Chain Length

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Dont forget to factor in your windless abilities, or your own should it fail.
Only an issue at a 1:1 scope when the windlass needs to lift the anchor and chain. For me that would be anchored in over 100'.
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Old 06-10-2019, 18:00   #28
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Re: Cruising Anchor Chain Length

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Only an issue at a 1:1 scope when the windlass needs to lift the anchor and chain. For me that would be anchored in over 100'.
Yep, when anchoring deep it is the last section that is tough to lift. Night before last we had to anchor in 90 feet behind a reef. Surprisingly the bottom was a sand/mud/shell mix that stuck to the anchor. So the poor windlass had to deal with 90ft chain, a 75lb anchor plus the weight of the congealed mud on the anchor.
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Old 06-10-2019, 19:37   #29
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Re: Cruising Anchor Chain Length

Everybody talks about chain. Well, it is heavy. If I am on the southeast coast of US where there is sand and mud, do I really need chain?
Thanks!
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Old 06-10-2019, 19:50   #30
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Re: Cruising Anchor Chain Length

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]]

30m of chain will lift off the seabed and form essentially a straight line at around 20-25 knots of wind, so the advantage relative to rope is lost. More chain helps this,
Show me a picture. I don't think this is even remotely accurate.
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