Mantus rode

[Delfin]

Originally Posted by ramblinrod

Yes "RUDE!"



It is when some get rude, when they feel they cannot adequately support their stated position, that it breaks down into offensive name calling, personal attacks, etc. that are so disruptive.

As you so amply demonstrate yourself on a regular basis.

[ramblinrod]

Originally Posted by Delfin

As you so amply demonstrate yourself on a regular basis.

I disagree.

I do not initiate disrespectful personal attacks.

If someone disagrees with me in a respectful manner, they will receive no grief from me. I will defend my position if I still believe in it, else I will rescind / correct my prior statement(s).

I always do my best to post in a gentlemanly manner.

When anyone treats me disrespectfully, I will call them out on it, respectfully, at least initially.

On occasion, after relentless disrespectful bombardment with personal attacks and name calling and such, I may lose my cool and respond in kind. I have tough skin but I am human.

As was the case here, in my opinion, for the reasons stated.

[evm1024]

Originally Posted by TommmD

So, I have a 35 lb Mantus on a rode 5/8" x 200' 8-strand spliced to 3/8"x15' d4 chain. This was built for my present 36 Hunter, 12,000 lbs + crew + gear.
Trading up to a 40' , 18,000 lbs + crew + gear.

This anchor felt oversized for the 36, so I'd like to think its more appropriate for the new boat. Plan on replacing the present 15'of chain with a longer length, somewhere between 50 & 100', but this is guesswork.

I'm in New England, if I anchor in 40' thats a lot, and 200 nylon+100 chain is over 7:1. That sounds like quite a bit. 100' of chain is 140 lbs + 35 lbs, all on the nose. 50 ft of chain cuts thats down to 105 lbs, but I'm thinking I should split the difference.

Is my thought process prioritizing the wrong thing here? How out of whack is all this? I just spoke to a friend with a 42' 24,000 lb boat (+ +) & he's carrying 300' of chain!

Thx for the thoughts,

Hi TommmD, Let's see if I can answer your questions more directly.

The 35# Mantus set up for your Hunter looks just about right. Someone knows what they are doing or if you speced it yourself you did great.

Moving up to a 40'er and 18,000 to 20,000 lbs will require an upgrade in your anchor size.

You will note that Mantus sizes anchors for 3 conditions - Lunch Hook, Cruising and Storm.

A lunch hook is just that, You stop for lunch and someone is always on lookout while you eat (etc). This size is just for a quick stop where you do not want to drop the main bower for some odd reason.

The "cruising" size is a good all round size for general anchoring in a more or less controlled environment. Pretty typical for the cruiser who goes out for a week or two and has a refuge in need near by.

The "storm" anchor is one size up from the cruising anchor and is the recommended size to those who go out into more uncontrolled situations where a "real" storm could come up without nearby refuge. Long therm cruisers, and such typically choose this size anchor.

You will note that Mantus gives 2 numbers for sizing their anchors. They specify boat length as a range and displacement max.

The numbers are not hard and fast but are a good indication.

If your boat has higher then normal windage you would select an anchor size based on length. If your boat has normal to lower windage you would select on displacement.

For a 40' 18,000# boat with typical or lower windage a Mantus 45# is recommended for a "Cruising" anchor. If the boat has High windage then select on length and a Mantus 55# fits the bill (39' to 43'). This assumes that you do not need an anchor for uncontrolled weather risks (go one size higher if you do).

On to your rode. Your 200' of 5/8" is fine. As for chain one rule of thumb is to have a boat length of chain, so 50' of chain would be fine. With a mixed rode of chain and rope you do not need a snubber so long as you have 20' or so of rope out to act as a snubber. Going to 100' of chain may require a snubber, Your choice.

All chain is required where there are coral heads. These bommies can come up to near the surface and can cut through rope in no time. No Coral, no need to 300' of chain (I have 275' of chain on my boat but that is me). Also, it is customary to have an all chain rode attached to a hardpoint in the boat with some line. The idea is that if you need to get away you will be able to let out all of your chain, Attach a float of some type and cut the line to free your boat. No need for that with a rope rode. You still need the bitter end attached to a hardpoint.

Scope - 10:1 scope is often specified for storm conditions. From the tables you will see that 10:1 retains most of the theoretical holding power of any given anchor. Basically you want the biggest anchor on the most scope you can get in a Named Storm.

The reality is that if you anchor in "normal" conditions and let out any more scope than the other boats have out in the anchorage you will not we very welcome as you crash into them.

Typically boats with all chain rode will let out somewhere between 3:1 and 5:1 while boats with a rope rode will let out 5:1 and 7:1. The more experienced they are the less scope they use generally speaking.

If your substrate is more mud than sand then an anchor with a larger fluke area will generally hold better.

OK, Hope that helps.

[Dockhead]

Originally Posted by Hesti

RYA course rules from the 90's: (not sure if they are still used):

Chain only: 4 x (depth plus height of freeboard)
Chain and rope: 2 x (depth plus height of freeboard) as chain plus 4 x (depth plus height of freeboard) as rope.

Having said that, there was the recommendation to let out more when the weather gets really nasty. Also, the recommendation was for Nylon as rope as it absorbs shocks nicely and thus reduces peak loads on the anchor and the boat.

I am still going by these rules, they are simple and easy to remember. So - by these rules, if you want to be able to anchor in 50 ft of (depth plus freeboard) and want to keep the boat light, that would be 100 ft of chain plus 200 ft of rope plus something to let out in really bad weather. With the 100 ft of chain, you could also anchor chain only in 25 ft of (depth plus freeboard).

4:1 scope was taught, at least in the UK, for decades, and you still find a lot of people here using that much.


I think we now know that 4:1 is a little light except in very deep water.




This is what Peter Smith says about it:


A 3:1 ratio of rode-length to water-depth should be considered minimal ("1" being the vertical distance from the seabed to the bow roller, not the waterline, at high tide). Generally speaking about 5:1 is appropriate. Typically you should set the anchor at the same scope it will be left at, in order to be sure the anchor can re-set itself again should it pull out. However, it may be necessary to set it at a higher scope and then pull in some of the rode.
In bad conditions, the ratio can be increased up to around 8:1. There is little benefit in going beyond this point, and boaters using scopes of 10:1 and higher are gaining almost nothing from their efforts and huge swinging circles. At 8:1, the maximum angle of pull on the anchor is already capped at just over 7°, and of course the scope must be doubled in order to halve the angle (i.e, even very large increases in the scope result in angle reductions of only several degrees). Considering the desire to lower the angle against the practical problem of longer rodes and increased swinging circles, 8:1 is roughly the 'sweet spot'.



Scope vs catenary (Rocna Knowledge Base)




This explains the geometry of it, and particularly, the diminishing returns as scope increases. I think 8:1 is the most which should be used, and that only in shallow water.


But 4:1 is little and should be used only in special circumstances -- tight anchorage, calm conditions, good bottom, etc. Except in deep water.




Scope has a different effect in deeper water -- which is the effect of the greater mass of chain and catenary. 4:1 in 100 feet of water is equal to 6:1 in 20 feet for 8mm chain in 40 knots of wind (see Peter's chart in the previously linked article). Therefore it is wrong to use a simple rule of thumb like x times the deepest water you ever anchor in. I have been through three days of gales in 30 meters of water, on 100 meters of chain, without issues, and consider 3.3:1 to be quite ok for 30 meters for my case -- which involves nearly half a ton of 1/2" chain.

[Dockhead]

Originally Posted by ramblinrod

. . . I recommend having a standard anchor, a storm anchor (50 - 100% bigger) . . . .

Most people these days recommend sizing the bower anchor as a storm anchor.



If your bower anchor is so small, that you could even practically store and deploy an anchor which is 50% to 100% bigger, then your bower is too small!


The bower should be the largest anchor than you can reasonably handle, which excludes having a much bigger one stored away some place.

Originally Posted by ramblinrod

Rule 5: The opposite end of the rode. The bitter end should be secured to the boat, such that if the boat dragged backwards at hull speed, with the anchor firmly set, and suddenly came up short at the end of the rode, the rode will remain secure to the boat, with no damage. (I have performed anchoring training for newbies on their boat, to find the rode bitter end, not even connected to the boat.) For all chain rode, you will also need a chain stopper, to ensure the load on the rode, is not transferred to the windlass.

Whenever not actually in the process of being hauled in or out, the chain should be made fast to the boat in some manner which is as strong as the chain, or as strong as the attachment to the boat can be made, whichever is less. But this should not be at the bitter end. Some people use a snubber for this, but that is very bad practice -- the snubber by design is weaker and vulnerable to chafe. The chain lock or belaying strop should be considered a fundamental part of the ground tackle and should not be the weakest link.


The bitter end should NOT be secured like that. Once you've lost control of the chain and it runs all the way out, you want it gone. The correct approach to this is to secure the bitter end with a light lashing to an eye bolt -- just strong enough to prevent the chain from being lost if you accidentally power it all the way out (don't ask me how I know this can happen ). Hang a ceramic or stainless steel knife next to it so that you can get rid of the chain quickly in an emergency.

Originally Posted by ramblinrod

Rule 6: Total rode length. For the standard rode, this needs to be at least 10 times the maximum depth + bow height, you ever expect to anchor in.. . Some who use all chain rode, may claim less is acceptable. I disagree. Once one reaches a circuit [certain?] wind velocity vs vessel windage (could be as low as 20 knots, especially if the boat your are considering is a deck salon with solar arch, dinghy on davits, and full enclosure) that removes the effective catenary in the chain, it acts pretty much identical to a nylon rode, and does not reduce the importance of total length vs depth any significant amount.. . .

This is true, but that "certain" wind velocity is different, depending on how much chain is out. Therefore, you need less and less scope, in deeper and deeper water. It is wrong to say "x times whatever maximum depth", whatever that is, and certainly not 10x, which is overkill even in shallow water. See: Scope vs catenary (Rocna Knowledge Base). No one carries 500' of chain -- most ships don't even have that much. I regularly anchor in 100' of water -- 100 meters or 330 feet of heavy chain is absolutely fine.

[Dockhead]

Originally Posted by Pete7

. . . Rule 3. "At least one boat length This has been a long standing rule"
Of what, rode? Who has decided this is a long standing rule? So one boat length is suitable for 30 knots of wind? really?

Rod is talking about how much chain, in a mixed chain-rope rode. I think you misunderstood him. One boat length is indeed the old rule of thumb, but I don't know any objective basis for it. Sounds OK to me, but I don't use mixed rodes and don't have experience with them.


If you're sailing a performance cat or smaller mono, then you might be forced to use a mixed rode, but I really prefer all chain, personally, because of chafe issues.

Originally Posted by Pete7

Rule 4. "One cannot secure the boat to the ground tackle by chain alone"
Oh I think you can.
"or it could rip the boat apart in a blow""
Okay, does this happen often in your neck of the woods?

Well, he means you need a snubber. It's true that uncontrolled snatch loads through the ground tackle really could rip your boat apart.




I'll tell you a funny story about snubbers -- in some discussion on here years ago, I had an argument with someone who insisted that above a certain boat size and chain size, snubbers are not needed. I didn't believe him. But he gave as evidence -- ships don't use snubbers. So I thought about this and started experimenting, and lo and behold, I discovered that I really don't need a snubber except in extreme conditions. I don't think I've rigged my snubber in two or three years. There's certain an explanation in physics for this -- once there's a certain weight of chain out, it becomes almost impossible to snatch up against it.



Moral of the story is to always listen to people who disagree with you

[Dockhead]

Further reading about anchoring on shorter scope, in deeper water:


https://www.distantshores.ca/boatblo...ater-scope.php


From Steve Dashew, who uses as little as 2:1 in very deep water:


SetSail FPB » Blog Archive » More on Anchors and Sizing


Dashew, a great boat designer and great yachtsman, and the author of the Cruiser's Encylopedia, has this to say about scope and how much chain to carry:


"Now let’s consider scope. Old time anchors require five-to-one scope to attain good holding. But the modern types can get by with less. The Manson, Rocna and Fortress showed little difference between three and five-to-one scope. The Manson hit the max test load of 5000 pounds at both three and five-to-one.

. . .


"[T]he last question is…how much chain do we carry? Remember the free lunch, or lack thereof? Here is where it comes into play. Let’s start by looking at anchoring risk factors. Poor holding, hurricane or stronger gusts, a bit of sea sweeping in, we’ve got this covered with the BFA. So we don’t worry about dragging. And besides, we can always offset extreme anchoring load scenarios coupled with poor holding with a judicious application of power. What we do worry about is fouling something on the bottom and not being able to recover our main anchor.
"Now a bit of exotic math. The area of a circle, or more aptly stated the area of the bottom swept by a given length of chain, is 3.14 times the square of the radius. So a little extra chain on the bottom geometrically increases the swept area and thereby the risk of fouling the anchor. Hence our theorem: (BFA+heavier chain) X (reduced scope)² = a lot less swept bottom and significantly reduced bottom fouling risk.

"How does this exotic math work out in the real world? On Wind Horse and Cochise, with the Rocna on the former and Manson the latter, we have dragged a single time in close to 100,000 nautical miles of cruising. We typically carry about 240′ of chain, although Cochise has a little more at roughly 275′. In shallow anchorages our norm is to set the anchor on three-to-one scope, including the height of the bow roller in the scope equation, and then once set bring the chain back to where we have a two-to-one scope. As the water gets deeper this approach begins to bring catenary into play. We have seen situations where we got reasonable holding in 180’+ of water using 300′ of chain."

So much for 10 times the depth.



Dashew with his great experience can afford to be somewhat less conservative. I don't ever use less than 3:1, but find that is plenty in 100 feet of water. I like 6:1 in shallow water, if I have room, but in benign conditions I don't mind shortening up from there.


Note well what Dashew says about the DISADVANTAGE of greater scope -- namely geometrically increasing risk of fouling the chain on the bottom. Just putting out more chain is not a free lunch.



As Dashew says, the amount of scope you need depends not only on the depth of the water, but also on what type of anchor and how big it is. A large, good anchor needs less scope than a small, poor one.




BFA in Dashew-speak = "Big Freaking Anchor" -- that is, the largest anchor you can practically handle.






Here is a good video showing the actual behavior of an anchor at only 50 feet, on 3:1 scope:

https://www.youtube.com/watch?v=w4qO_dIegaM

[ramblinrod]

Originally Posted by Dockhead

Here is a good video showing the actual behavior of an anchor at only 50 feet, on 3:1 scope:

Interestingly, the linked video seemed to support my prior post.

See: Scope vs catenary (Rocna Knowledge Base).

http://kb.rocna.com/kb/Scope_vs_catenary

Interestingly, the Rocna Knowledge Base article seems to also support my original post, with the exception they recommend:

A) A heavier anchor over more chain (not surprising as they make money off of heavier anchors and not off of more chain).

B) A 10:1 vs 8:1 max scope. Meh. Maybe due to the heavier anchor recommendation that they suggest.

[Dockhead]

Originally Posted by ramblinrod

Interestingly, the linked video seemed to support my prior post.

In what way does that video support something you wrote?


Maybe I misread it, but I thought you recommended carrying 10 times as much chain as the deepest water you would anchor in.


I disagree with that advice, because (a) 10:1 is overkill in any case; and (b) the amount of scope you need is not subject to such a simple rule of thumb -- you need more with a lighter anchor, a worse design anchor, and shallower water, and you need less with a bigger anchor, a better design anchor, and/or deeper water.


The video show very good results in deepish water (only 50 feet) at 3:1 scope. In really deep water, like 100', you get more or less ultimate holding power at 3:1 on chain, especially heavy chain.



Your "rule" would mean I would need 1000 feet of chain, since I regularly anchor in 100' of water, which is quite absurd. 1000 feet of 1/2" chain would weigh one metric tonne or 2200 pounds. Not even ships carry that kind of length of chain.



You don't choose chain length that way. You choose it generally by how much your boat can comfortably carry, but stopping at whatever value is the maximum you could ever possibly need, which is probably 300 feet or so even for hard core high latitude voyagers. Nobody carries more chain than that. Note what Steve Dashew, one of the world's most experienced and knowledgeable long-distance cruisers, who goes to all kinds of crazy places including Greenland and Antarctica, writes about it in the linked article -- he carries 265 feet of chain on his latest boat.



300 feet, or say 100 meters (330 feet) is a bit of a magic number for rode length, at least for heavier chain, because it will give you something beyond ultimate holding power at 50' of depth (about 6:1), but also something near ultimate holding power at 100' because of the decreasing requirement of scope with water depth.



There is really not any need for more chain than that, which is why no one carries more than that. Large ships, which anchor in much deeper water than we do, typically carry five shots of chain, which is 75 fathoms or about 135 meters (maybe 10 or 12 shots for really large vessels). According to your "rule", 5 shots is not even enough for 40' of water. And they don't use snubbers.

[Dockhead]

Originally Posted by ramblinrod

. . . Interestingly, the Rocna Knowledge Base article seems to also support my original post, with the exception they recommend:

A) A heavier anchor over more chain (not surprising as they make money off of heavier anchors and not off of more chain).

B) A 10:1 vs 8:1 max scope. Meh. Maybe due to the heavier anchor recommendation that they suggest.

You missed the part, further down, where Peter discusses the effect of depth on required scope.


As I said before, it is nonsense to prescribe a one-size-fits-all scope as x:1 for whatever depth, anchor type, and anchor size. 8:1 is very good for a bad storm, anchored in 20' of water, with a good and large anchor. It's not needed in 50' of water (4:1 or 5:1 is plenty), much less in 100' of water (3:1 is plenty).



No one needs 1000' of chain, to anchor in 100' of water, nor do you need even 500' of chain.


I spent most of last summer anchored in 100' of water, by the way, so this is not a merely theoretical discussion for me.

[Pete7]

Originally Posted by Dockhead

Well, he means you need a snubber. It's true that uncontrolled snatch loads through the ground tackle really could rip your boat apart.

In a smaller yacht we certainly wouldn't plan on anchoring in those conditions or even just boisterous. Been there, gave up and moved. The motion on board is just too uncomfortable for a yacht weighing 5000 kgs, particularly if the waves are frequent. It's one of the downsides of a smaller yacht.

Actually we have used a snubber in calm conditions, but mainly to avoid the chain moving on the foredeck when wind causes us to sail around the anchor. I really don't like a piece of chain grinding my GRP deck even if its only moving a couple of inches. Its also annoying trying to sleep in the v berth.

Strangely I agree with Rod and prefer the working anchor on the bow. The Rocna is small enough to deploy with one hand and therefore quick and easy to use. So we do often, even just stopping for lunch or a swim. We are just in that goldilocks zone, another few feet and we would need the next size up, have to use the windlass full time and the anchor wouldn't fit in the bow locker.

The big Fortress is stored below, but available just in case.

[Dockhead]

Originally Posted by Pete7

. . . Strangely I agree with Rod and prefer the working anchor on the bow. . .

Ha, ha. Is there a controversy even about that?

[Pete7]

Originally Posted by Dockhead

Ha, ha. Is there a controversy even about that?

People have been excommunicated for less

I am just not saying (I claim the 5th Amendment even though I am English) whether that is agreeing with Rod, or using a working anchor, the reader is welcome to make any assumptions they like

[Dockhead]

Originally Posted by Pete7

People have been excommunicated for less

I am just not saying (I claim the 5th Amendment even though I am English) whether that is agreeing with Rod, or using a working anchor, the reader is welcome to make any assumptions they like

Well, as opposed to deploying it at the stern? (Seriously advocated by some on here!). Or as opposed to using the biggest anchor possible as the bower?


I'm actually a big proponent of the advice of making your storm anchor your working anchor -- which is what you will hear from Morgan's Cloud, Steve Dashew, Peter Smith, and just about every serious expert. If you have access to the Morgan's Cloud site, you will find a very good discussion about why effectiveness of anchors goes up out of proportion to size, and there's seemingly a great leap in effectiveness when anchors get over 100 pounds. This is why everyone recommends even sacrificing chain weight or length if necessary to get to a bigger anchor. In my experience, accumulated over 30 years in boats of different sizes and with anchors of all different sizes, this is really good advice and correct anchoring theory.



To get an anchor to set in difficult conditions, you want as much weight as possible -- weight in absolute terms, not as a proportion to your boat size -- pressing down on the sharpest and best balanced fluke you can get. And this same combination will keep the anchor set in difficult conditions, and especially, help it reset in a wind shift.


So the advice from all of them is to use the biggest anchor you can reasonably handle on an everyday basis, and that is already your storm anchor. If your everyday working anchor is smaller than what you can reasonably handle, it's too small! I agree with this.




The only point on which I might disagree slightly with the experts is on chain weight. Dashew is a well-known proponent of using light G70 chain in order to be able to have more weight in the anchor. The theory being that in ultimate conditions, the chain will go bar tight anyway and you lose the value of catenary.


I don't think that's exactly right, at least not when anchor chains get to a certain size and length. The catenary effect becomes massive and never really stops working, with enough of big enough chain (and evidence of that is ships not needing snubbers). This could be explained mathematically I guess. I sometimes get sick of carrying 330kg of chain in my bows but every time I have to sit out a blow at anchor, I cast such thoughts aside as I feel all that chain working to dampen snatch loads and keep me safely attached to the seabed. In my opinion, you need BOTH a BFA AND a BFC, for ultimate anchoring power. To reduce the negative effect on trim and polar moment of inertia, of carrying a large fraction of a tonne of chain, one can design a boat (like the Sundeer is designed) with the chain locker midships and down near the keel. This is actually not rocket science, and my next boat will be like that.

[Delfin]

The tests Evan Starzinger did on a Manson Ray, Rocna and one other modem design I can't remember, but which were all over 100#, illustrates the point that heavy anchors behave much differently than the same model in a lighter weight. The winner of this yest was the Ray, which on lighter weights isn't going to beat a more modern design, but at 100# was the best by a fair bit as I recall.

Point is, length of rode questions change depending on what anchor is at the end of the rode, and what the seabed is. I've anchored in sand/shell for fishing for hours in 25 knot winds at 1:1.5 scope without dragging an inch. The anchor weighs 176#.