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Old 05-01-2021, 11:03   #76
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Re: Anchoring with 4:1 Scope?

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Originally Posted by Kelkara View Post
This got me thinking ... In that situation, my first thought would be to shackle my second anchor rode onto the primary to increase scope. I'm sure your boat has a second anchor, so if that option was a sensible choice you would have thought of it ... could you explain your reasoning for selecting short scope instead? was it because there was no room to swing, or because joining the rodes was impractical in storm conditions, or because you'd rather the risk of dragging than the risk of losing both anchor rodes if you have to cut loose, or because you had plenty of experience with that anchor at 2.3:1 in "pretty bad storms" and totally trust it, or is your ground tackle so oversized that it would hold a battleship on any scope, or do the "rules" change at depths of 40+m?
Some would disagree. I have read a cruising guide to Labrador where similar conditions exist. There the perceived wisdom is to set two anchors; one down slope inshore and one ip slope off shore and have them meet in a heavy ring. The ring then has some rode to connect it to the boat, long enough to account for the high tides.

This is to hold you relatively in one place and guard against grounding if the wind shifts 180°.

I have never done it and it sounds like a pain, especially short handed.

The idea is you have limited swing room, you cant just let out more scope. And there are frequent wind shifts, which can float you up toward the beach and leave you grounded when the tide rolls out. But if you anchor our far enough to safe guard against that, well then you are in some seriously deep water.
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Old 05-01-2021, 11:56   #77
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Re: Anchoring with 4:1 Scope?

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Some would disagree. I have read a cruising guide to Labrador where similar conditions exist. There the perceived wisdom is to set two anchors; one down slope inshore and one ip slope off shore and have them meet in a heavy ring. The ring then has some rode to connect it to the boat, long enough to account for the high tides.

This is to hold you relatively in one place and guard against grounding if the wind shifts 180°.

I have never done it and it sounds like a pain, especially short handed.

The idea is you have limited swing room, you cant just let out more scope. And there are frequent wind shifts, which can float you up toward the beach and leave you grounded when the tide rolls out. But if you anchor our far enough to safe guard against that, well then you are in some seriously deep water.
Sounds like a Bahamian mooring, or you can just set bow and stern anchors. I am confused about the part about
"There the perceived wisdom is to set two anchors; one down slope inshore and one ip slope off shore and have them meet in a heavy ring."

Could it be you have that backwards? Inshore would be up slope, no?
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Old 05-01-2021, 12:15   #78
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Re: Anchoring with 4:1 Scope?

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Originally Posted by Don C L View Post
Sounds like a Bahamian mooring, or you can just set bow and stern anchors. I am confused about the part about
"There the perceived wisdom is to set two anchors; one down slope inshore and one ip slope off shore and have them meet in a heavy ring."

Could it be you have that backwards? Inshore would be up slope, no?
The up slope anchor is facing down slope and visa versa. The up slope anchor is nearer the shore and keeps you from being blown off the shore. The down slope anchor is in deeper water and protects from being blow ashore.

The problem with a single anchor, as noted in the Greenland tale is the anchorage is too small for adequate scope. And the tidal range is on the order if 15’ to 20’. So anchor in 20’ at low tide and you need 200’ of scope for 5:1 for high tide, nearly 400’ of swing at low.
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Old 05-01-2021, 12:26   #79
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Re: Anchoring with 4:1 Scope?

3:1 has always worked for me (44lb Spade on a 49' Hylas, world cruising for 3.5 years). I have stuck with that ratio on my current 70,000lb 72' MY which has an 85lb Forfjord. Early days with this boat/anchor but no problems yet.

I only ever once dragged after set. I never broke free after set. The one time I dragged I re-set with greater scope and still dragged. Everyone was dragging in soft mud.

Your mileage may differ.

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Old 05-01-2021, 14:33   #80
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Re: Anchoring with 4:1 Scope?

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Originally Posted by Kelkara View Post
This got me thinking ... In that situation, my first thought would be to shackle my second anchor rode onto the primary to increase scope. I'm sure your boat has a second anchor, so if that option was a sensible choice you would have thought of it ... could you explain your reasoning for selecting short scope instead? was it because there was no room to swing, . . .
Yes, no room to swing. The slope of the bottom was so extreme, that to even get on soundings you had to get within a couple hundred meters of the rocky shore. I had 100m of heavy chain out and could not have put out more even if I had had it.

And if that doesn't sound bad enough, the sea was full of icebergs and bergy bits. If one of those drifts over your anchor, you are toast. You desperately want shallower water, because the shallower the water, the fewer bergs can reach you. But with the slope of the bottom, you're lucky to have 30=40m, and small bergs can make it into those depths.

I slept with radar running and guard zones set, which not only guards against wandering bergs, but is a dandy anchor alarm too.

It was somewhat "challenging".

At least we didn't have to deal with darkness -- at 71N, 300 miles above the Arctic Circle, in summer time, the sun never even gets very close to the horizon.
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Old 08-01-2021, 07:04   #81
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Re: Anchoring with 4:1 Scope?

Here is my approach so chain length: I don`t think that the anchor is caring at all how much chain is going up to the boat. The anchor cares only about the horizontal force that pulls on him. If I feel happy with having 20 m/60 ft of chain on the ground plus 5 m of rounding to the vertical part - always, no matter what depth - I need only to add the water depth + the hight of my hull. It will show that more depth doesn`t require sooo much more chain.
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Old 08-01-2021, 07:06   #82
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Re: Anchoring with 4:1 Scope?

I'm a learning noob at anchoring. We just recently started anchoring out more this last summer and I've been taught 7:1 and 5:1. We have a 35lb Mantis on a 10,000lb 34' boat. To learn more I've been diving down on our anchor every time.

Not very exciting videos, but you might be interested to see how the anchor has set.

Anchor is burried
https://youtu.be/93K0IEePOG8

Anchor barely caught a rock
https://youtu.be/IJN5Goak9Dg

I'm thinking the amount of scope we've let out is way overkill, however there was nobody around so we had lots of room to swing. My opinion is as long as the rode doesn't completely lift off the sea bed you are good. (again, remember this is the opinion of someone that has only anchored 20 times)
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Old 08-01-2021, 07:31   #83
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Re: Anchoring with 4:1 Scope?

Frankly, there is no ‘official’ scope. There are just a lot of variables. Quality of the seabed, type of anchor, weight of chain, windage on the boat, wind speed, tide and current flow to name the main ones. In some situations 3:1 is plenty, in others 7:1 is not enough. I am happy if stopping for lunch say, 3:1 is ample when someone is keeping an eye on it. If one is leaving the boat for any length of time then lots need to be paid out.

I always set the anchor by backing up the boat quite firmly and then keep an eye on transits. I try to identify lit objects as transits too. Quite easy to use when my bladder alarm goes off at night.

GPS anchor watch devices or the chart plotter generally help. But from experience do not, the first time you use it, just set it and hit the bunk. One I used bleeped briefly once it hit the limit and thought that it’s job was done as we trundled through the anchorage. Another I used (IPhone) bleeped seemed to lose position and bleeped unnecessarily. Finally, make sure your crew are aware of the anchor watch device. One of my crew was woken by a bleeping alarm, hopped out of bed and switched it off, fortunately not harm done.

Finally don’t forget that the simple echo sounder can be set to monitor changes in depth when tidal range is small. Also AIS has a movement alert which can send a text message to one phone.

At the end of the day, if you are in a difficult anchorage you can always set an anchor watch so someone is awake and keeping an eye on your position.
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Old 08-01-2021, 07:38   #84
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Re: Anchoring with 4:1 Scope?

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There is no magic number here. More is always better. Panope's tests say nothing about this. His tests are intended to be extreme anchoring situations, not arguments for a new normal.

In general, the newer anchors set better and have greater ultimate holding power than most of the older designs (Danforth-style still wins, but in a narrow band of substrate). This is why we can get away with shorter scopes most of the time. But that doesn't mean one should deploy less.

It's all about trigonometry and force vectors. The longer the hypotenuse of the anchoring triangle the smaller the ultimate pull angle on the anchor, and the greater the horizontal force vector. All anchors work by digging in, and the greater the horizontal vector, the better they do this.

I believe it was Noelex (another great contributor to anchoring know how) cites research showing that rode ratios beyond 10:1 really make no measurable difference. I have laid to 4:1 or even 3:1 on very rare occassions, but unless I'm constrained by geography or other boats, I never willingly lay out less than 5:1. And if there's space, I happily put out more.
5:1 is our rule of thumb and I see no reason in most cases to shorten up on that. We have a 30 kg. SPADE on 10 mm chain as the main anchor, which we lay out in a) breezy or anticipated to be breezy weather, and/or b) overnights and up to 7:1 scope. I have to say that the SPADE's "flaw" is a good one: it tends to sink so well that we bring up a considerable amount of the bottom in muddy conditions and we are going to install a washdown pump to shorten this process. I will point out at this stage that our boat is 12 metres long and is a pilothouse cutter in steel. Sixteen tons, in other words, of fun with plenty of windage. We worry not about being hit, but about hitting others, and therefore "too much is probably just enough". Your mileage may vary.

In conditions of calm to 10-12 kts for a "stop and drop" or "lunch/nap" situation, we will use our Fortress FX-37 at 5:1. This anchor has a five metre 3/8" chain leader and about 50 metres of 5/8" nylon three-strand spliced to it. I can hoist it by hand if I choose when we are at 1:1 over it.

We were in a situation last September, however, when Hurricane Teddy gave a glancing blow to Cape Breton while we were self-isolating at dock in Port Hawkesbury. On the advice of locals, including a local tugboat skipper pal, who had seen the docks torn up the previous year, we tied off AROUND the slip as the cleats were judged too weak for 60 knots on the beam. We also dropped anchor out in the otherwise empty mooring field, tied off ALL our rope rode (about 300 feet) with fisherman's bends to the bitter end of the chain (about 165 feet) and backed into the slip. We then evacuted to the second storey of the clubhouse for about 30 hours and got to watch the boats dance in their slips. A combination of mostly favourable wind shifts, top gusts of just under 60 knots by my estimates and partial protection from land and the worst of the fetch saw us come through with only a few scratches and some shredded fenders.

However, we did notice that, despite being "docked and locked", there had been some force on the anchor, when was itself a Hail Mary move should the docks have come apart (something I saw in Antigua in Hurricane Gonzalo in 2014 and wish not to see again, thanks). The SPADE was so deeply buried that it took a few attempts at 1:1 scope the day after to break out the anchor and about 45 minutes of swearing-filled effort to get the heavy mud hooked on it to return to the bottom. We had an anchor float and I assume "back pulling" on this helped to draw out the anchor to a point, but it was heavy going to get it back aboard.

That's a good problem to have in some respects, but "decaying hurricanes" aren't the usual problem to solve.
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Old 08-01-2021, 07:40   #85
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Re: Anchoring with 4:1 Scope?

For those of us who regularly anchor in a fairly well protected bay with stern tie options, I've rarely gone beyond 3:1. Sometimes, if the bottom is like a "bowl" with shallow sides and a steep slope, 2:1 is fine with a stern tie.

Anchoring out in a bay with no stern tie, I believe we've never gone beyond 5:1, but then again, we are most often not going to be out in a storm, if we can avoid it.

We currently use a 33lb Lewmar (Bruce style) claw, 50' of chain and rope rode. Before this, we used a smaller spade anchor, with 300' of chain, for our 35' 14000lb boat.

When we replaced our chain with a heavier chain, new windlass and new anchor, the logic was that we don't need the weight of 300' of chain on board when we rarely use more than 120' of it, so we opted for 50' of chain and 250' of rope rode.

I must admit, I don't like having to gingerly pulse the windlass when the rope-to-chain splice goes around the gypsy, or it can jam. (Maxwell RC series windlass/gypsy). Never a concern with all chain.

I've watched all the videos Steve has made with great interest and while we have a few different cnchors onboard, we use the claw because the only time it has dragged is when we put it down in a specific spot (not a good spot to anchor), on solid rock, at 2:1 for a video shoot we were doing. I doubt any anchor would do well on a relatively smooth rock surface, but the weight of it kept us stationary enough until the job was done (on a calm day).
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Old 08-01-2021, 07:43   #86
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Re: Anchoring with 4:1 Scope?

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It's rare that I let out as much as 5:1; usually 3:1 has been enough with my Manson Supreme. I like a heavier anchor with less scope rather than lighter anchor with more.
I've never heard anyone advocate 7:1 scope before--that just sounds ridiculous.


I take it you don't have an ASA sailing qualification where it clearly states 7:1 scope. Not that anyone follows that in real life but it's right there in the books and exam.
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Old 08-01-2021, 08:11   #87
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Re: Anchoring with 4:1 Scope?

Conventional wisdom (per CG exams) has been 7:1 with an all line rode - practically a 3:1-5:1 scope works for all chain, depending on many variables.

I've used 5:1 on a CQR with all chain with success for years. From my experience, an older CQR where the hinge and pin are worn will significantly underperform a new CQR. I also let the wind, not the engine, set the anchor. It appears many of the tests I have seen simulate backing down on an engine, not the gentle motion of the wind digging the anchor in.
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Old 08-01-2021, 08:16   #88
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Re: Anchoring with 4:1 Scope?

I've been very interested in this topic for all of the reasons that have been discussed. But I'm surprised that no one has really talked about the mathematics of the problem.

I found a good explanation at NauticEd and have used the "2 times depth + 50 feet" method ever since.

https://www.nauticed.org/sailing-blo...hain-and-rope/
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Old 08-01-2021, 08:33   #89
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Re: Anchoring with 4:1 Scope?

Here is what could happen or worse with not enough scope.

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Old 08-01-2021, 09:11   #90
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Re: Anchoring with 4:1 Scope?

I have the Excel and love it. It holds very well on a variety of substrates. I, however, still use 5:1 to 7:1 because of the 10+ foot tides in the Pacific Northwest. I have used it as a lunch hook at 3:1 and 4:1 in sand with some good current and wind with no issues. But its at your discretion. In this case more is better if you have room.

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