How Much Chain Rode

Nomad Willy said:

Octupus Is. should'nt have any fetch so why the snubber? Are you sailing and thus jerking on the line?

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When we anchor for several days in one location, I usually use the snubber line for a couple of reasons. The first, we don't get the chain noise from the pulpit rollers. The second, the snubber changes the angle of incidence? I think that's what it's called, maybe you guys know the correct term.

My pulpit rollers are 8ft above the water and when we get a stiff wind without the snubber, the chain on the rollers gets noisy when sailing back and forth. Can't say for sure, but sailing seems to be reduced with the snubber. I made the snubber line with a finished length of both sides right at 24 feet. By running through the forward Hawspipe and securing to the Samson post, it hangs down about 8 feet below the water with no strain. Our next test in wind we will try routing the snubber to one side or the other to the next Hawspipe back. Several people have recommended this to reduce sailing even more.

Nomad Willy said:

Bill wrote;
"Once the chain come bar tight there is no more centenary effect."

There's been lots of talk about that over the years but I don't put much stock in it.
First of all the catenary would be closer to the anchor and not visible. The catenary is not a linear arc. The chain droops like a hawky stick. It would take a lot more than wind to straighten out a chain rode. IMO. But I'm not supporting all chain. IMO catenary is mostly beneficial setting the anchor. A level pull on the anchor is important then.

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I made this point earlier and agree, that no way do you pull an all chain rode "bar tight", on a small boat anyway. Probably not even on a battleship.

Crusty Chief said:

Full moon tomorrow, .

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Check your lunar tables there Crusty!

makobuilders said:

There was a previous thread which discussed rope/chain versus all/chain. Perhaps seῆor NomadWilly can comment on this, but my question is, setting aside the issue of chafe of the nylon line:

Wouldn't it be more advantageous to just have a short length of extremely heavy stud link chain (eg. 6 feet of 1" stud link) attached to the anchor, followed directly by the nylon rode?

Basically dispensing completely with the typical 1/2 boat length of "normal" size chain. It seems that wind/surge load would have to be rather high for the 60 lbs of stud link and then the anchor to be raised above horizontal.

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Nice to be remembered .. thanks.

Several years back someone dug up some research and found that catenary on a rode is not linear at all. One would think (re a straight line) the droop or catenary would be at the mid point along the rode. Not so and I'm quite sure it varies w different scope and lengths of chain. Shorter scope would have the catenary closer to the anchor and longer scope closer to the mid point but not to the mid point until the rode is horizontal. Te research said the maximum cat was about 20% of the way up the rode .. probably w all chain. With all line being much much lighter the catenary would probably max further up the rode but still lower than mid point.

But exactly under what circumstances the cat become ineffective? .. I don't know. But having not used more than 15' of chain ever cat obviously had little to do w the fact that my boats have never dragged. Pacific is "peace" and little wind is the norm at night in the Pacific Northwest so that also was a factor. My boating goes (went) in spurts so that also helped. But I have anchored in 50 knot gales twice and 30 to 40 knot winds many (30?) times. My experience indicates cat (catenary) is a minor player in anchor performance. And my opinion is that ground tackle weight is most wisely spent at the anchor. In the "186lb" example above putting 50lbs into the anchor would be far better than 186lbs into the rode. And if one is bent on using the remainder of the "186lbs" but it in line available .. in the locker.

But if I had a 45' boat I definitely would have a rode much or considerably different than the one I have now. If the boat was stern heavy I'd have lots of chain. But not all chain. Not all because I could have a very long rode in a combination rode and that may keep me off the beach (sand or rocks) some day. But I would have more than "a few feet of chain". If the boat was bow down (heavy) I'd have a combination rode w considerably less chain than line. And I'd work hard to get the boat in trim.

So Mako I would say probably more and lighter chain would be better. Up to about 30 - 35% of rode. But keep in mind that most combination rodes rarely let out line at all .. or just a small amount. So perhaps 20% chain would be best for cat performance. Lots of variables to consider.

78puget-trawler said:

I made this point earlier and agree, that no way do you pull an all chain rode "bar tight", on a small boat anyway. Probably not even on a battleship.

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PT,
I agree but Peter Smith (Rocna) says so. I don't take much stock in what he says and I'm not going to spend a lot of time proving it. But I'm quite sure normal anchoring won't pull out the catenary. But how much pull on the rode will reduce the cat to be ineffective? It's a degree thing and how valuable is it in the first place? Don't know but I (like you) believe we won't get a chain bar tight w all chain out. I believe the anchor to be far more effective on anchoring performance than chain. Steve on Panope showed rodes at quit an angle w lots of tension on and the shanks w their shackle end (of the shank) down in the bottom. Many were surprised to see that. That alone shows cat is'nt as important as we thought. But lots of people think it is.

Crusty Chief,
OK good. I never have the chain noise so rarely think of that.
I'm keen on bridals though as we sail a lot and really dislike it.

If you are truly setting the anchor by powering back on it, you are by definition eliminating the catenary of the chain. I've seen all-chain rodes pulled completely tight on a variety of boats, typically at around 25 knots depending on boat design.
A snubber doesn't change the angle of incidence or pull one bit; it essentially creates a combination rode.

Chain accomplishes a number of things that casual or occasional boaters may not have particular need of. Beside dampening the motion of the boat in fair weather conditions, it eliminates chafe on the bottom in those conditions, such as when only mild current shifts or breeze directions cause the boat to move about. I've recounted here the time when I saw our anchor (or the end of the shank, I should say when I got up one morning, off our port quarter with the half-buried chain running parallel to the boat all the way on up past the bow... we were lying to the chain due to a breeze shift during the night. Likewise, we have brought in several yards of mud packed chain when weighing anchor.

And it reduces the exposure of the rode to chafe at the boat as well, though of course care with snubbers/bridles requires chafe protection too... it's just that they are more eminently and quickly easy to replace should they be compromised by chafe.

I never thought about it before, but as the anchor gets heavier on larger boats, is there a point where all-chain is required to ensure engagement with the windless gypsy? Would a combo chain/rope rode engage securely with a 175lb anchor and maybe 50-75 lbs of chain? Are combo gypsies even available above 3/8" chain size? I only remember seeing chain gypsies available for my Maxwell 3500.

Caltex,
Chain on the end of the anchor shank actually inhibits anchor penetration because it slices into the bottom w dificulty. Anchor penetration is better w a short length of cable (2 or 3') because the end of the shank goes into the bottom better.

But you can't see the catenary near the anchor. The chain near the bow pulpit may look straight but lower down and especially near the anchor it may (probably) is drooping w considerable catenary. I can offer no proof but belive it to be true. Re chafe good point.

Twistedtree,
I'm quite sure you're right. At some point in size it will ceast to be available. Then all chain or cable is a given.

With a reel winch all rode types and combinations are available. Studded chain, shackle, heavy chain, shackle, standard chain for the boat, shackle, nylon line or whatever.
But w/o the reel winch all chain of one size it the only option and long rodes are way too heavy.

So much speculation...hard to add anything....other than just practice with what you have....go from there.

Chain on the end of the anchor shank actually inhibits anchor penetration because it slices into the bottom w dificulty. Anchor penetration is better w a short length of cable (2 or 3') because the end of the shank goes into the bottom bette

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And you know this how? So I take the shackle also inhibits "penetration"? Have you ever actually observed how chain interacts with mud and sand? Do you have any concept of the forces at work when you set an anchor and the effect on the rode? Or at least considered why no one does this?

Good questions George,
Go back to Steve's (Panope) anchor vids and see the rode pulling up at maybe 45 degrees and the end of the shank obviously being pushed down onto/into the seabed. The shank not at 45 deg like the rode at all. People don't guard against this because they don't know the shank does this. Most people think (as I did) that the shank is well above the sea floor (more in line w the rode) before I saw Steve's vids.

Re the shackle see the thread "Shackle bolt in shank or chain" post #1. The pic is upside down but you can see the small and narrow shackle that I bought through XYZ anchors. Minimal size/profile so will penetrate the bottom better allowing the shank to run deeper .. probably allowing the anchor to dig/penetrate deeper. There is some speculation I admit but see the evidence and draw your own conclusions. In the pic you can see a recent rode of mine that employed the short cable.

Having dove down on plenty of anchor rodes and watching the videos...if the shank and chain do not penetrate...the substrate is hard enough that peneration at that point is not necessary, necessary holding power is achieved. If the bottom Is softer, needing more penetration...it will..... even with large shackles and chain....

Anchors are designed to dig, even with shackles and chain to whatever depth they need to....to acheive the necessary holding.....yes at some point they dont....but that isn't because of the rode...it is because of the anchor design and or scope or bottom material.

Capt.Bill11 said:

Once the chain come bar tight there is no more centenary effect.

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As I recall, and if I had time I would confirm before posting but I don't so for now my possibly flawed memory will have to do, the physics of the situation dictates that the force required to lift the first 5' of chain off the bottom of a level sea floor 60' deep, with 420' of chain rode (or any other 7-1 scope of any appreciable length), is greater than the breaking strength of any typical anchor chain.

MYTraveler said:

As I recall, and if I had time I would confirm before posting but I don't so for now my possibly flawed memory will have to do, the physics of the situation dictates that the force required to lift the first 5' of chain off the bottom of a level sea floor 60' deep, with 420' of chain rode (or any other 7-1 scope of any appreciable length), is greater than the breaking strength of any typical anchor chain.

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I once had a conversation with an architect/ engineer friend of mine about catenary. He was designing a screened bird enclosure that was constructed with poles and steel cable covered with netting. It was big and the cables all had catenary. I asked him why he didn't just pull them tight. He said they would break before you could pull the catenary out of them. He could do the math which is way beyond me.

Chain and shackles won't burry in a hard bottom of course.
My reference was to Steve's anchor setting vids and the bottom was quite soft. And soft bottoms benefit most from penetration.

Yes Travler and HopCar,
There are many posts about chain rodes pulled "bar straight" and I thought it was about time that myth got exposed. Of course this is in favor of chain rodes and I usually don't beat the drum for chain but the more myths we can bust or truths we can uncover the better.

MYTraveler said:

As I recall, and if I had time I would confirm before posting but I don't so for now my possibly flawed memory will have to do, the physics of the situation dictates that the force required to lift the first 5' of chain off the bottom of a level sea floor 60' deep, with 420' of chain rode (or any other 7-1 scope of any appreciable length), is greater than the breaking strength of any typical anchor chain.

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I have given this a little more thought, and stand behind my conclusion, above, that the pull on an anchor at the end of a 7-1 scope all-chain rode will always be horizontal (if the bottom is). But, there is an exception and it has to do with scaling. If the boat (and its anchor/chain/rode) were a scale model, the chain could be strong enough to lift off the bottom. But, scaling up to real trawler size prevents (fortunately) that same result. Even Divinci got in trouble with scaling -- his helicopter would work if small enough but could never get the lift necessary to overcome gravity at any practical size. A tangent to another thread concerned seaworthiness as a function of size. I don't remember who argued what, but I think someone forgot about the consequences of scaling.

MYTraveler said:

As I recall, and if I had time I would confirm before posting but I don't so for now my possibly flawed memory will have to do, the physics of the situation dictates that the force required to lift the first 5' of chain off the bottom of a level sea floor 60' deep, with 420' of chain rode (or any other 7-1 scope of any appreciable length), is greater than the breaking strength of any typical anchor chain.

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Ok, so the more important question, with proper anchor and chain size, at what scope do you start lifting the first five feet of chain off the bottom when anchoring in 60' of water?

Ted

Ted
To answer your question the catenary has to be calculated. In our discussions beginning this year I designated this load as the "ultimate catenary load" to distinguish from the "ultimate load with stiff rode".
Data needed to calculate the catenary are
-) height / water depth (60')
-) specific chain weight per length
-) length of the chain
Results of the calc would be the tensile force whose horizontal component gives the holding force keeping our vessel in place.

To be more precise: as long as the chain length exceeds those 60' water depth the scope at which the chain starts to lift at the ground (ultimate catenary) depends on the horizontal force acting at the chain ...

best regards / med venlig hilsen
wadden

Chain and shackles will bury in a hard bottom....they will saw into coral too.

Usually they dont bury in a hard bottom, not because they cant, it's because they usually don't have to.

If a big old fat anchor can bury, why can't a shackle and chain ?

O C Diver said:

Ok, so the more important question, with proper anchor and chain size, at what scope do you start lifting the first five feet of chain off the bottom when anchoring in 60' of water?



Ted

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Ted
Some figures, all for 60' depth, specific chain weight 1.55 lb/ft, zero slope angle at ground.
-) slope 3:1 (180' chain): holding force 371 lbf / chain load (tensile force) 464 lbf
-) 5:1 (300 ft): holding 1114 lbf / load 1207 lbf
-) 7:1 (420 ft): 2228 lbf / 2321 lbf
-) 9:1 (540 ft): 3713 lbf / 3806 lbf, increasing suddenly to 7519 lbf if chain becomes stiff
-) ...
Figures will differ if specific chain weight changes.
The more chain is out, the higher is the horizontal force (holding force) needed to lift the last feet of chain. But the resulting tensile load might exceed the chain strength if a sudden gust pushes us back and the chain becomes stiff ...


best regards / med venlig hilsen
wadden

101TUG said:

chain + line is really American way you never saw that in Europe

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Most sailing boats here in the old world are doing it the "American way", 10-50 feet of chain followed by a nylon rope. While the majority of full displacement power boaters here in Europe don't care of the chain weight at the bow, most of them have an all chain rode and will apply a snubber for shock absorbance.



best regards / med venlig hilsen
wadden

Makobuilders,
I'm going to change my response to your question a bit. If you put your hunk of studded chain about 10' up from the anchor it would probably be close to ideal.
I wonder why you asked this question though because almost nobody here has a ground tackle settup that would retrieve such a rig. One would need a reel type winch.

An easy way to experiment would be to arrange a rope/line, chain ect on a slope approximately the same angle as your typical scope between two fixed points w a little droop in the line. Then attach a weight along the line or whatever and measure the angle of the line at the lower end .. to horizontal. Find the weight position that produces the flattest line at the lower end ... more horizontal.

You don't seem to get it Scott.
Of course chain and shackles are pulled below the surface in/on a soft bottom. It's a matter of degrees. More is better so rode that slices more easily down in the bottom substrate has an advantage. Better is better. That's all. Like dual exhaust is better than one. Just a little better but better.

waddenkruiser said:

Most sailing boats here in the old world are doing it the "American way", 10-50 feet of chain followed by a nylon rope. While the majority of full displacement power boaters here in Europe don't care of the chain weight at the bow, most of them have an all chain rode and will apply a snubber for shock absorbance.



best regards / med venlig hilsen
wadden

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So .... Just like us Yanks. That's flattering .. thanks.

Just seems to be a matter of those that care about weight and those that don't. In addition to that trawlers are concieved as heavy .. heavy duty .. skookum .. robust .. strong. All percieved as good and there will be a high percentage of those that think weight is good in a group of trawler skippers. And it even emulates the boats we were named after .. North Sea Trawlers.

MYTraveler said:

I have given this a little more thought, and stand behind my conclusion, above, that the pull on an anchor at the end of a 7-1 scope all-chain rode will always be horizontal (if the bottom is). But, there is an exception and it has to do with scaling. If the boat (and its anchor/chain/rode) were a scale model, the chain could be strong enough to lift off the bottom. But, scaling up to real trawler size prevents (fortunately) that same result. Even Divinci got in trouble with scaling -- his helicopter would work if small enough but could never get the lift necessary to overcome gravity at any practical size. A tangent to another thread concerned seaworthiness as a function of size. I don't remember who argued what, but I think someone forgot about the consequences of scaling.

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Even if it were true that the last few feet never lift off the bottom or move to the semi-vertical position, which I don't believe to be so, the snatch load would still be transmitted to the anchor, no?

Having scanned this thread I did not notice any mention of windlass sizing. If you are intending to up-size the windlass for larger chain, you should also consider the overall weight of the new anchor plus the longest length of 3/8 BBB chain (vertical lift from deepest anchoring location), and make sure you get a windlass with capacity to spare. Having once had to pull up 200ft of chain by hand (using the windlass come along) because of a failed solenoid switch, I definitely do not recommend this approach!!

Capt.Bill11 said:

Even if it were true that the last few feet never lift off the bottom or move to the semi-vertical position, which I don't believe to be so, the snatch load would still be transmitted to the anchor, no?

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Yes, there will always be jerk load on the anchor (though the catenary acts as a damper), but never in excess of the load the weakest link in the chain can handle. Isn't the real question, though, how to best maintain horizontal pull on the anchor? As for whether the force on the anchor chain can ever be enough to lift the chain off the sea floor, you may be right, but physics suggests otherwise.

I think a level pull on the anchor and chain induced catenary is a good thing. But I think it's over sold and over rated. Looking at Steve's vids consistantly showing the anchor shank pointing down on the bottom instead of pointing up the rode speaks volumes about the need or lack of need for catenary. Even though the rode is ramped up at 20 to 30 degrees. Catenary is a good thing but much less necessary than we thought before.

psneeld said:

Chain and shackles will bury in a hard bottom....they will saw into coral too.

Usually they dont bury in a hard bottom, not because they cant, it's because they usually don't have to.

If a big old fat anchor can bury, why can't a shackle and chain ?

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My thoughts also...

Nomad Willy said:

I think a level pull on the anchor and chain induced catenary is a good thing. But I think it's over sold and over rated. Looking at Steve's vids consistantly showing the anchor shank pointing down on the bottom instead of pointing up the rode speaks volumes about the need or lack of need for catenary. Even though the rode is ramped up at 20 to 30 degrees. Catenary is a good thing but much less necessary than we thought before.

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Eric, I think you are only partly right there. Sure, even at quite short scopes, the shanks in Steve's videos did appear to stay down on the bottom, I suspect that was because of the downward force on the shank imposed by the mechanics of the fluke digging down into the bottom. However, once the anchor is set, if the forces on the rode were sufficiently great that the catenary is overcome and the rode does pull directly on the shank in an upwards direction, the subsequent levering action would begin to raise the shank, and therefore also the fluke tip, and a break-out could well follow. So, overall...the catenary IS a really important factor in staying put I would say.