Using your new anchor with kinetic rope

[Dockhead]

Originally Posted by thinwater

. . . That does not mean smaller anchors hold better in all ways. I'm not making that argument. I'm saying only that at the same setting force it is obvious that a smaller anchor will go deeper. That is what it must do to hold the same force. There is no other way.

OK, thanks, that is useful and interesting.


But the key phrase is "for the same setting force", and it is manifestly not true, that small anchors can equal the holding power of larger anchors just by diving deeper at a given force.

[Izikalvo]

Originally Posted by thinwater

I suggest you try this in firm sand with, say a 2-pound Guardian and a 15-pound Guardian. At the same force, the large anchor will barely submerge the shank, while the small anchor may be 2-3 feet under ground and very difficult to recover. I've done just this in testing, many times. Didn't always enjoy it.



I parked the boat using a large (oversize) Fortress off the bow. I then pull smaller anchors to failure off the stern. The large Fortress stays on top, while some of the smaller anchors go quite deep.



That does not mean smaller anchors hold better in all ways. I'm not making that argument. I'm saying only that at the same setting force it is obvious that a smaller anchor will go deeper. That is what it must do to hold the same force. There is no other way.

Great explanation, therefore if your anchor has the right shank/fluke/ground/chain angle, and it is too small it will set than plaw under the surface Ie. break out.

If it is too big it will not completely penetrate the surface due to lack of power of the boat, maybe the wind or current will help, maybe not.

But the right size will gust go deeper when forced to do so.

So..... do not oversize new design anchors, no need.

[thinwater]

Originally Posted by Dockhead

...This boat will be subjected to 762daN of force at 40 knots (per ABYC formula), and 429daN at 30 knots....

No. That is NOT what the ABYC H40 Table 1 values mean. They are the recommended working load for the equipment, not the actual load. In fact, measured loads are 3-5 times lower than these. Which is good.



You can reach ABYC values if anchored on all chain, at short scope, with long fetch and in water shallow enough that the waves are beginning to get steep. For example, 4-6 feet of water at 5:1 scope with 15 miles of fetch in 15- to 20-knots. that is the basis of the standard. But with normal anchoring practices (in this example, anchor farther out in 15 feet of water) the actual load will be several times lower.

[thinwater]

Originally Posted by Izikalvo

Great explanation, therefore if your anchor has the right shank/fluke/ground/chain angle, and it is too small it will set than plaw under the surface Ie. break out.

If it is too big it will not completely penetrate the surface due to lack of power of the boat, maybe the wind or current will help, maybe not.

But the right size will gust go deeper when forced to do so.

So..... do not oversize new design anchors, no need.

That's not exactly what I said or meant. I said smaller anchors go deeper at equal load.


Areas with poor holding (very soft mud, for example) may require oversized anchors. Or rather oversized as rated for sand. They're not really "oversized" for the substrate.

[Lodesman]

Originally Posted by Dockhead

I was hoping that you would run the numbers and see for yourself. We discussed it in the old linked thread.


Playing with these numbers is very illustrative, and will show you that you objectively do not have a "reasonable chance of ensuring the chain never gets to that point". With 12mm chain, if you have 150 meters of it, and have all that chain out, then you can't pull the catenary out of it without breaking it. But let's take a more typical case -- a 36' boat using 60 meters of 1/4" chain, and displacing 8 tonnes.

I did run the numbers - if you say the average boat has 60m of 1/4" chain I believe you, but also believe that the average boat has inadequate anchor tackle. I have 300' of 3/8" and would add more if I was anchoring in more challenging locales.


What that means is (a) a good enough and big enough anchor that a certain amount of angulation can be tolerated; and (b) a snubber, to absorb shock when catenary is no longer doing that.

I'm curious about what you use as a snubber? And how you have it set up? At the load that catenary is "no longer doing" it, wouldn't the snubber also be stretched out to the point where it is no longer insulating the vessel from direct chain tension?

You don't size an anchor to be barely adequate in perfect conditions -- prudent sailors, notwithstanding what some on here have said, oversize the anchor as much as is reasonably practical. It should not be 2x bigger than needed to give the exact holding power needed to prevent dragging, it should be 10x bigger if possible, even 20x. Every "x" is your margin of error for (a) non-ideal seabed, which can reduce holding force by 5x or more; (b) non-ideal angle of pull on the anchor, which WILL happen, when conditions get up to where the catenary gets pulled out of the chain; (c) non-ideal set, which can happen for a lot of different reasons. Murphy's Law states that these factor will tend to occur simultaneously.

Don't assume I make do with "barely adequate." I have no idea what was original fit in my 1977-built boat, but the PO had upsized to a 37 lb CQR clone with 300' of chain, and I went up further with a 72 lb Rocna. I have an enormous Guardian (Fortress' less-blingy cousin) and was bequeathed a 45 lb genuine CQR (kept as a spare), which will be replaced with a Spade or Spade-like copy (M2 or Vulcan, see how they test/review).

Another reason for oversizing the anchor is a case which Dashew specifically writes about, and something I have, terrifyingly, experienced myself -- what if you are forced to anchor in short scope?


In Northeastern Greenland, the bottom slopes down incredibly, with depth of 1000 meters apparently sounded just a few cables from shore, in the back of Scorseby Sund. The bottom is rocky, the water is full of ice, and it is a hellish place to anchor. Your best bet is normally the DEEPEST place as far back in a cove as you can get, some place from which the bottom doesn't slope down anywhere, so that some silt accumulates to get your anchor into. This means anchoring in deep water, and close to the rocks. So the summer we were up there, we rarely anchored in less than 30 meters of water, and sometimes 40 or more, so we were often on as little as 2.5:1 of scope. We succeeded -- and weathered at anchor gales with gusts touching 50 -- only because the anchor was big enough to have enough excess holding power to still provide adequate holding power at that scope.

I'm not new to fjordland anchoring techniques. It's not uncommon in BC for boats to hang between a stern-tie to a stout tree ashore and their bower hanging at max scope downslope.


This can be seen from this table from Peter Smith's site:



Attachment 210261


Even with heavy, 12mm chain in deep water, you can clearly see the bar-tight shape of the catenary.

Anyone that only has 48m out in 50 kts of wind, needs to give their head a shake. You implied that it would be virtually impossible to achieve zero catenary with 150m of 12mm chain without snapping the chain - so I assume you agree that it is possible to equip in such a way that catenary will never disappear.


Yet another reason to use a larger anchor, and a snubber, is soil mechanics. This post explains it: https://www.cruisersforum.com/forums...ml#post2853735


You want OVERKILL with your anchor for this reason, also -- repeated cyclical stress on soil causes it to lose its strength and fail. If your anchor is sized to give you barely enough holding power in that storm, it may pop out after a couple of hours of cyclical loads. The more oversized the anchor is, the less stress on the soil, and the less the risk of this kind of failure. This tracks real life experience.

If soil fails by liquefaction to hold 2000sqcm of anchor, it will probably fail to hold 3000sqcm of anchor. Maybe the soil engineer can weigh in on this, but surely it makes more sense to spread the contact area over a much larger area - and more chain equals contact over a much larger area.

[Dockhead]

Originally Posted by thinwater

No. That is NOT what the ABYC H40 Table 1 values mean. They are the recommended working load for the equipment, not the actual load. In fact, measured loads are 3-5 times lower than these. Which is good.

You can reach ABYC values if anchored on all chain, at short scope, with long fetch and in water shallow enough that the waves are beginning to get steep. For example, 4-6 feet of water at 5:1 scope with 15 miles of fetch in 15- to 20-knots. that is the basis of the standard. But with normal anchoring practices (in this example, anchor farther out in 15 feet of water) the actual load will be several times lower.

Yes, I'm well aware of this, largely from your excellent work on this with load cells


But I think the design load is (by definition!) the right load to use in this thinking. Especially if you're going to be counting on catenary for shock absorption rather than a snubber.


I think the numbers show that you will need a snubber at far less than extreme conditions, on most boats, and everyone's experience backs that up I think.

[thinwater]

Originally Posted by Dockhead

Yes, I'm well aware of this, largely from your excellent work on this with load cells


But I think the design load is (by definition!) the right load to use in this thinking. Especially if you're going to be counting on catenary for shock absorption rather than a snubber.


I think the numbers show that you will need a snubber at far less than extreme conditions, on most boats, and everyone's experience backs that up I think.

Yup, good points.

[Dockhead]

Originally Posted by Lodesman

If soil fails by liquefaction to hold 2000sqcm of anchor, it will probably fail to hold 3000sqcm of anchor. Maybe the soil engineer can weigh in on this, but surely it makes more sense to spread the contact area over a much larger area - and more chain equals contact over a much larger area.

These geotech phenomena occur near the limit of the soil's shear strength. So if you are near the edge of that with 2000cm2 of anchor then you'll be a bunch further away from it with 3000mc2 so much less at risk.


The point is that it is dangerous to push up to the limits of an anchor's holding power; this is only just one more argument, on top of the main one, which is that you anchor in a variety of bottoms, some of which have 5x less or even less than that, the shear strength of a good bottom.


Concerning chain contact with the seabed adding holding power -- research shows that this effect is negligible. Thinwater can probably weigh in on this.

Originally Posted by Lodesman

I did run the numbers - if you say the average boat has 60m of 1/4" chain I believe you, but also believe that the average boat has inadequate anchor tackle. I have 300' of 3/8" and would add more if I was anchoring in more challenging locales.

90m of 9.5mm chain has critical tension of 1237daN -- enough to deal with the ABYC design loads for 40 knots. You do not use a snubber? You've never seen stronger conditions than that at anchor?

Originally Posted by Lodesman

I'm curious about what you use as a snubber? And how you have it set up? At the load that catenary is "no longer doing" it, wouldn't the snubber also be stretched out to the point where it is no longer insulating the vessel from direct chain tension?

I see you just don't have experience with snubbers. Good for you -- you're lucky if you've been able to do without all your cruising life.


I grew up cruising with my Dad, and he taught me to use a snubber religiously. We weren't anchored (i.e., no cocktails) until the snubber was rigged and the chain lock locked. But those were smaller boats with lighter chain. I learned only much later that a snubber is really not needed with heavy chain and a larger boat, until fairly strong conditions. I don't rig one unless conditions over 20 knots are expected.



But yes -- a properly designed snubber of course will take the force and give proper damping, in any conditions. You need to have several for different conditions. My usual one is 15 meters long, 25mm nylon octoplait. Breaking strength from memory is 12 tonnes, or 50% more than the chain, so it is well within its optimum stretching load when the chain is at WLL. You tune snubbers to give the right amount of stretch -- make it longer to get more, shorter for less, use a lighter one for the same stretch at less length.

Originally Posted by Lodesman

Don't assume I make do with "barely adequate." I have no idea what was original fit in my 1977-built boat, but the PO had upsized to a 37 lb CQR clone with 300' of chain, and I went up further with a 72 lb Rocna. I have an enormous Guardian (Fortress' less-blingy cousin) and was bequeathed a 45 lb genuine CQR (kept as a spare), which will be replaced with a Spade or Spade-like copy (M2 or Vulcan, see how they test/review).

Originally Posted by Lodesman

I don't assume anything, but there have been those in this thread saying that larger anchors are not required, so this is a continuation of that discussion. 78 pound Rocna on a 47' boat sounds entirely decent to me; you're probably more over-anchored than I am (100 pounds, 54' 20-odd tonnes).

Originally Posted by Lodesman

"You implied that it would be virtually impossible to achieve zero catenary with 150m of 12mm chain without snapping the chain - so I assume you agree that it is possible to equip in such a way that catenary will never disappear.

Yes -- the numbers show that with 150m of 12mm chain, there will be catenary even at breaking strength of the chain. But with 100m of 12mm chain, already not.


Also don't forget that you can't always put out 100m of chain -- there are many cases where swing room is limited.


You you cannot indeed assume that it is possible to be sure that your catenary will never disappear. On the contrary, it is really important to assume the contrary -- that your anchor is big enough to still be adequate with half of its holding power taken away due to angulation, and have a snubber to deal with shock loads.

[Lodesman]

Originally Posted by Dockhead

Concerning chain contact with the seabed adding holding power -- research shows that this effect is negligible. Thinwater can probably weigh in on this.

I'd love to see the research. I seriously doubt it is negligible, once the chain has buried itself a bit.

90m of 9.5mm chain has critical tension of 1237daN -- enough to deal with the ABYC design loads for 40 knots. You do not use a snubber? You've never seen stronger conditions than that at anchor?

I do use snubbers, and played around a bit with how they're rigged. There are plenty of opinions out there, but seems to be little in the way of 'scientific' advice as to how to get the best out of them - I've got upgrade plans and want to benefit from your experience.
We've frequently ridden out 20+ kts on the hook, but to my memory only anchored once with the winds 30G40, and have been attached to a mooring buoy in 40-45 kt winds, but for the most part have avoided crappy weather, or found suitable shelter. Even professionally I can't recall hanging on an anchor in anything over that, but we would generally scope for 60kts.

I grew up cruising with my Dad, and he taught me to use a snubber religiously. We weren't anchored (i.e., no cocktails) until the snubber was rigged and the chain lock locked. But those were smaller boats with lighter chain. I learned only much later that a snubber is really not needed with heavy chain and a larger boat, until fairly strong conditions. I don't rig one unless conditions over 20 knots are expected.

That makes sense. Rigged in the "traditional" way, I never found the snubbers to be of much benefit.

But yes -- a properly designed snubber of course will take the force and give proper damping, in any conditions. You need to have several for different conditions. My usual one is 15 meters long, 25mm nylon octoplait. Breaking strength from memory is 12 tonnes, or 50% more than the chain, so it is well within its optimum stretching load when the chain is at WLL. You tune snubbers to give the right amount of stretch -- make it longer to get more, shorter for less, use a lighter one for the same stretch at less length.

See this is what I'm getting at. But how is that rigged? Do you just cleat that off, or have you special fittings? What sort of attachment do you use on the chain and how much excess (loose) chain do you put out?

Also don't forget that you can't always put out 100m of chain -- there are many cases where swing room is limited.

You you cannot indeed assume that it is possible to be sure that your catenary will never disappear. On the contrary, it is really important to assume the contrary -- that your anchor is big enough to still be adequate with half of its holding power taken away due to angulation, and have a snubber to deal with shock loads.

True swinging room is sometimes limited. To that I say it is probably not prudent to anchor in a confined space when wind conditions will likely test the limits of your anchor's holding capacity. For the most part I've avoided anchoring with the herd, and when I haven't been able to avoid it, I've chosen to anchor further from the beach, and kept an eye on the weather. I still thinks it's odd to have a huge anchor for its massive holding power, only to use it in a way that would halve that hold.

[a64pilot]

Originally Posted by Izikalvo

So..... do not oversize new design anchors, no need.

If we always anchored in sand of infinite depth, I’d agree, but sometimes there is a foot or less of sand over hard bottom, then bigger is better, sometimes we anchor in mud, and there bigger is better.
But really what tips the scale is that I don’t think anyone can come up with situation of where a bigger anchor won’t hold as well as a smaller one.
So I believe that within reason going as large as your boat can handle has no downside, except higher cost of course. But amortized over a cruising lifetime, that is even a small amount.

[Dockhead]

Originally Posted by Lodesman

True swinging room is sometimes limited. To that I say it is probably not prudent to anchor in a confined space when wind conditions will likely test the limits of your anchor's holding capacity. For the most part I've avoided anchoring with the herd, and when I haven't been able to avoid it, I've chosen to anchor further from the beach, and kept an eye on the weather. I still thinks it's odd to have a huge anchor for its massive holding power, only to use it in a way that would halve that hold.

There are no herds, ever, anywhere I anchor. I haven't even been below 50N in a few years. Limited swinging room can follow from all kinds of circumstances. In a really bad blow, you want SHELTER, and that often imposes limits on room. 100 meters of chain out means a swinging circle one cable in diameter - can you always find such a space, with good shelter, when the weather turns bad?

I'm afraid I can't always; hence I am very grateful to have ground tackle which works excellently on 3:1 scope when required. That requires the anchor to be big enough, that 50% of it's theoretical holding power, and not in an ideal bottom, either - is up to the job.

[Dockhead]

Originally Posted by Lodesman

See this is what I'm getting at. But how is that rigged? Do you just cleat that off, or have you special fittings? What sort of attachment do you use on the chain and how much excess (loose) chain do you put out?.

I think I do it like everyone. I splice loops in the ends of my snubbers and just hook them on a bow cleat, and run them over the second unused bow rollers. Attached to the chain with a rolling hitch. Any amount of loose chain which is more than the amount of stretch you will get is enough. It's not really rocket science, but then again, I've been doing it since I was a teenager.


Chafe is an issue with snubbers, and I break them from time to time. A Dyneema leader would be a good antidote to this.

[j.g.evans]

Another reason for all chain is it hangs vertically when there is not much wind and current. For years I cruised a 30' monohull with 10 m of chain and 9/16 nylon line. Many mornings after wind and current swinging the boat I would wake up with the line wrapped around the keel, rudder and even caught in the prop. On a 40' monohull I had all chain and never had this happen. For many years I had no windlass and manually hauled in 5/16 chain and a 40 lb anchor. OK and fast.

[Nicholson58]

Originally Posted by a64pilot

No.
I have no idea what kinetic rope is, but a combo chain / three strand nylon rode is very stretchy, but is not as desirable as all chain, often due to the chafing issue. If your never near coral and rock, then I see no problem with it, but I am sometimes in rock.
I try to avoid coral if at all possible.

Never near coral or rock or weed or grass. That is, if you are assured of always anchoring in sand. Plan to always dive on it.

We have 121# ROCNA and heavy all chain rode. The massive anchor penetrates hard sand and dense grass. The best insurance you can buy.

[Beau.Vrolyk]

Originally Posted by Izikalvo

We are playing with a new idea since anchors becoming lighter, would you consider using a new-gen light anchor with 10-meter chain and the rest of the rode be a kinetic Nylon rope that can be stretched?

We estimate that this kind of setup will dismiss the usage of a windlass with boats up to 40ft.

what do you think?

Obviously, the length of the chain you need depends upon the sort of bottom you're anchoring upon. But, everything else you say is correct in our experience.

We use 150' of chain followed by 300' of nylon. Our procedure is to only have chain contacting the bottom and have as much nylon as possible.

Numerous tests have proven that an all-chain rode will fail much more quickly than a chain + Nylon rode, as the myth of a catenary absorbing shocks is quickly proven in high winds and large waves.

As to picking a size boat that could dispense with a windlass, I think you're mistaken to even try. First, it depends upon the strength of the crew, young and strong vs old and weak. Second, it depends upon the depth of the water. To keep the nylon off the bottom you'll need a lot of chain in deep water (We often anchor in 150' of water.) Finally, the ability to haul up the anchor by hand is entirely dependent upon the wind speed and current. None of this has anything to do with the size of the boat.