Cruising Anchor Chain Length

[jmh2002]

Originally Posted by s/v Jedi

...It’s what you do when your boat is named Jedi ;-)

Fair play

[s/v Jedi]

Originally Posted by Dockhead

You and Jedi are both right. Of course, you're right, that it's not true, and is not intended seriously even, that there is no such thing as a too big anchor. Naturally there are downsides to handling giant anchors.


HOWEVER, Jedi is also right, and what he says is kind of a watchword amongst real anchoring experts. Couple reasons:


1. Larger anchors work better disproportionate to the increase in size. Some effect of soil mechanics I guess. In fact some people say that there is a threshhold at about 100 pounds where anchors start to work quite differently and much better. I have experienced this so I believe it, although I haven't seen any actual scientific research.



2. You can't size your anchor based on best-case seabed conditions. The difference in holding power between a weak bottom and a good one could be 10x. So while a much oversized anchor may be overkill in good bottoms, it may well not be overkill in a poor on, and make the difference between holding or not.


3. You don't always have the choice to use a lot of scope, and there are many cases where it is desirable to use short scope even if you are not forced to (crowded anchorage, foul bottom, no swinging room, etc.). A much bigger than specified anchor will work much better on short scope. Dashew has written that he anchors 90% of the time on 2:1 scope. He can do that because he has a 240 pound or whatever anchor.


Now I don't have a 240 pound anchor nor do I anchor on 2:1 scope, but if your anchor is inadequate to hold you at fairly short scope then in my book it's inadequate period.


All these are really, really good reasons to have a bigger anchor.


My Spade is two sizes bigger than the chart recommends, and I for sure wouldn't want anything smaller. It's 100 pounds so just into the "100 pound magic" range. I did have a 121 pound Rocna before but with the roll bar it was hard to handle and I went down a size when I replaced it with the Spade.


Note that weight on the bow is not, for most people, any kind of consideration. Why? Because it's small potatoes compared to the weight of your chain. I have 750 pounds of chain in my anchor locker; plus or minus 50 pounds in the anchor is meaningless.

I agree with Dockhead on anchoring, but to Wingsail, who I can’t seem to quote in iPad Safari: even though my comment on how to size your anchor was tongue in cheek, for most boat designs it is actually about the biggest anchor that fits their roller system.

I always get the BS about weight being bad for performance. This is why you leave your anchor and chain ashore during regattas, problem solved. When you’re leaving port to sail the world, you bring that big anchor that works everywhere, in as many seabed conditions as possible and you take an all-chain 400’ primary rode because that works everywhere. If you’re not ready to do it right then you better stay home. If you don’t (and many don’t) then it’s the rest who’s gonna have to help save you and your boat in the places where the compromise anchor setups don’t work. I remember one instance, anchored off Key Biscayne near Miami, where we were the only boat not dragging in a violent thunderstorm. A 50 footer with a 110 pound Bruce dragged.

[s/v Jedi]

Originally Posted by wolfgal

Ah ha! this is of interest!!!

i've seen folks carry long and heavy chain in the bilge in the main cabin and send it up through a hatch (a bit of hoisting for the both of them) and, since then, have been wondering WHEN i'd see someone make this modification. it makes so much sense to me.

if you have the time, id like to know more...

wolfgal

This is how Steve Dashew designed the Sundeer 64. It also allows the chain locker to be narrow and very tall. My chain locker is 6’ tall and fills to the top with 400’ of 3/8” chain.

BTW, 400’ of 3/8” chain is a full barrel, which is the most cost effective way to buy chain

[jmh2002]

Originally Posted by Dockhead

I think the real problem with this approach, and the reason you don't see it much, is simply the headaches it gives designers in laying out accommodation.

I tend to agree. At a minimum a chain locker back by the mast is using prime value space in the hull, whereas that that little nook in the very forward bow isn't useful for as many other things.

Plus, the chain needs to be run all the way back there to the mast too, and to do this nicely and acceptably for most people that means running it under the deck in some way.

Which gives the designers another headache that they would prefer not to have.

I'm not saying it can't be done - it can be of course.

Instead I'm agreeing with you that most designers (and to be fair, most owners too) just don't want to make the necessary compromises to enable this.

[jmh2002]

Originally Posted by s/v Jedi

This is how Steve Dashew designed the Sundeer 64. It also allows the chain locker to be narrow and very tall. My chain locker is 6’ tall and fills to the top with 400’ of 3/8” chain.

Yeah, for some strange reason Steve Dashew likes to design these important systems in the very best possible way, in a way that works, and in a way that is just so damn nice to use in every day cruising...

Why would someone do that? It's bizarre!
And it's no wonder some people don't like him or his boats!
(being sarcastic, in case this doesn't translate over the internet).

[model 10]

[QUOTE=Auspicious;2998923]You're going to have to provide footnotes here. I have yet to encounter or hear of scenario when a new-gen scoop anchor does not set better and hold better than a plow.


A good example is the anchorage in Isla Mujeres, MX. There are a few spots with no grass, but for the most part it's grass over thin mud. The last time I was there I dove on some boats near me after a wind event. My Rocna as usual was full of grass and mud up to the roll bar, just the tip was still stuck. Another 10 knots and it would have been a bowling ball. I couldn't see anything of the other 3 anchors. Two of the 3 had a CQR.

[Dockhead]

I've been there, and done that. That "bowling ball" thing is typical Rocna behavior and it comes from the roll bar, not the scoop shape. Spade doesn't do that at all. [QUOTE=Ecos;2999117]

Originally Posted by Auspicious

You're going to have to provide footnotes here. I have yet to encounter or hear of scenario when a new-gen scoop anchor does not set better and hold better than a plow.


A good example is the anchorage in Isla Mujeres, MX. There are a few spots with no grass, but for the most part it's grass over thin mud. The last time I was there I dove on some boats near me after a wind event. My Rocna as usual was full of grass and mud up to the roll bar, just the tip was still stuck. Another 10 knots and it would have been a bowling ball. I couldn't see anything of the other 3 anchors. Two of the 3 had a CQR.

[s/v Jedi]

What do y’all think of the Mantus M2 anchor? Didn’t hear or see anything about it yet. Seems perfect as a spare primary to keep disassembled in the bilge.

https://www.youtube.com/watch?v=pZhha6FAueY

[Dockhead]

Looks like an economy version of the Spade, without the fabricated shank.

But if it's as good as the original one, it should be a winner.

Originally Posted by s/v Jedi

What do y’all think of the Mantus M2 anchor? Didn’t hear or see anything about it yet. Seems perfect as a spare primary to keep disassembled in the bilge.

[wingssail]

Originally Posted by s/v Jedi

...I always get the BS about weight being bad for performance. This is why you leave your anchor and chain ashore during regattas, problem solved. When you’re leaving port to sail the world, you bring that big anchor that works everywhere, in as many seabed conditions as possible and you take an all-chain 400’ primary rode because that works everywhere. If you’re not ready to do it right then you better stay home...

Weight being bad for performance is not BS. Maybe on a 64' boat there is some latitude for bigger anchors. On many boats weight in the ends is a performance factor and affects pitching in seas.

Of course when leaving to sail the world we take everything, everything we own, actually (what else would we do with it?)

And what we own is what we need. It certainly includes several anchors and big anchors. What we carry in the bow however is not the biggest which will fit or all the chain. On the bow we carry what makes sense considering the holding power and our experience. We have confidence in the 44lb Bruce for every seabed type we have encountered. The other anchors, and the biggest, and all the chain, are below and aft of the bow. It's available if we need it (as we have, twice).

We have placed the windlass well aft of the bow (about 10'). The chain falls to the hull, about 6' down. We then drag it aft to a locker at cabin sole level next to the mast. If we need to deploy suddenly the windlass will pull the chain forward without our intervention (there are skid plates on the thresholds).

Few boats our size (43') can accommodate this, but we can and consider ourselves lucky to be able to do so.

Since the chain is located in the cabin it must be cleaned while recovering. A powerful wash down system gets most of it. If there is still mud or debris we scrub it with a brush where it crosses the deck to the windlass.

This approach has worked, worldwide. We've not yet needed to be rescued. Nor have we, since changing to the 20kg Bruce, had a problem with dragging or inability to set. I don't see how having the 30kg anchor up there, or 400' of chain, would have improved our outcomes any. I am very glad we didn't carry all that extra weight around up in the bow for the last 23 years to have only used it twice since when it was needed we got it out easily enough. I do think it would have caused pitching and a wetter boat, and certainly a slower one.

By the way, sailing ships traditionally kept their biggest cables in the hold, not the forepeak.

A side benefit is that the chain can dry out, even on rough passages. We have been able to continue to use the same 275' section of 5/16 HT since we bought it in 1993. It's been re-galvanized twice. It is not rusty.

[Canderes]

The 3:1 Giudline is wrong!
Most anchors break out if they are lifted by more than 8°.
If there is a strong wind, the chain tensions, therefore a 6-7-fold water depth is required. explore the breakaway angle of your anchor. ask the manufacturer if necessary and solve the problem geometrically!
After setting the anchor, steam it in with 3.000 upm on your machine for approx. 60 seconds to test it.
when anchoring, I prefer to sleep in the bow cabin. I can hear the anchor there.
if the place allows it, give a lot of chain. but this can lead to problems with ships arriving later, because the skippers don't expect the anchor on the overlong chain!
I NEVER set an anchor buoy, because the line of the buoy with the anchor can get stuck and break out the anchor when the ship swings. if you absolutely want to set a buoy, use the buoy with a suitably long line and attach a weight to the line. set the buoy with the weight NEAR to the place where you drop the anchor.
ps: my sailing experiences are much better than my english experiences :-)
regards sailing.czaak.at

[noelex 77]

Originally Posted by Canderes

The 3:1 Giudline is wrong!
Most anchors break out if they are lifted by more than 8°.
If there is a strong wind, the chain tensions, therefore a 6-7-fold water depth is required. explore the breakaway angle of your anchor. ask the manufacturer if necessary and solve the problem geometrically!

It is important to understand than the anchor shank is not lifted at the same angle as the chain.

Here is an Ultra. The chain angle is over 8°. As expected, the anchor shank angle relative to the seabed is much lower than the chain angle.

The anchor will have less ultimate holding power than would be the case if a much longer scope was used, but as you can see there is no “break out”.

[Montanan]

Originally Posted by jmh2002

I tend to agree. At a minimum a chain locker back by the mast is using prime value space in the hull, whereas that that little nook in the very forward bow isn't useful for as many other things.

Plus, the chain needs to be run all the way back there to the mast too, and to do this nicely and acceptably for most people that means running it under the deck in some way.

Which gives the designers another headache that they would prefer not to have.

I'm not saying it can't be done - it can be of course.

Instead I'm agreeing with you that most designers (and to be fair, most owners too) just don't want to make the necessary compromises to enable this.

Now I have never seen or heard this being done, but just imagine if one was able to rig a system wherein the barrel of chain was transported to a hollow in the keel of the boat so as to add weight for stabilization when sailing and to store it out of the bow while sailing. It would require some kind of a conduit or puller to gently get it to travel from the primary lifting windlass towards the inner keel storage space, a low powered drum with a few wraps of chain around it would seem to avail enough friction to draw chain from the bow to the keel in a metal tube. A barrel's weight of chain being used for righting the boat and providing for long length of rode for deep anchorages.

[Canderes]

Originally Posted by noelex 77

It is important to understand than the anchor shank is not lifted at the same angle as the chain.

Here is an Ultra. The chain angle is over 8°. As expected, the anchor shank angle relative to the seabed is much lower than the chain angle.

The anchor will have less ultimate holding power than would be the case if a much longer scope was used, but as you can see there is no “break out”.

i'm not talking about chain angle! I'm talking about anchor (shank) angle!
Handbreit

[Dockhead]

Originally Posted by Canderes

The 3:1 Giudline is wrong!
Most anchors break out if they are lifted by more than 8°.
If there is a strong wind, the chain tensions, therefore a 6-7-fold water depth is required. explore the breakaway angle of your anchor. ask the manufacturer if necessary and solve the problem geometrically!

Not true at all!


Only the very worst and undersized anchors will break away at 8 degrees.


Here is a graph of holding force vs. angulation from Alain's site:


Anchor


Even the worst anchor is getting 80% of its holding force at 8 degrees, and a good anchor (green line in the graph) will still have 50% at 20 degrees. 3:1 is 18 degrees without catenary, and if your anchor has 10 times the holding power you need, as it should, then 50% of that gives you a 500% safety margin.


If your anchor is properly sized and of good quality, 3:1 scope is plenty. I've been through storms on 2.5:1 and Steve Dashew typically anchors at 2:1.



More is better, of course, and I will put out 5:1 or 6:1 if I have room and enough chain (I carry 330 feet), but it's important not to make a fetish out of it. If you need to anchor with 3:1, you can, provided your anchor is decent and you set it properly.




To put some numbers to that:


According to Alain's formula, an average 45kg anchor should develop 4.5 tonnes of holding force in "good", not "excellent" seabed. A really good anchor (I have a Spade) might produce twice the holding power predicted by the formula, maybe 9 tonnes, beyond the breaking strength of my chain.


Yet, in 60 knots of wind, typical forces might be 1200kgf (ABYC 3.3 tonnes).



So do I need 6:1 scope in a strong gale with 40 knots of wind? 40 knots of wind amounts to ABYC 1500kgf, but typically 500kgf, on a 54 foot boat? Of course not. 50% of my anchor's holding power in a decent, not excellent bottom, is nominally 2.25 tonnes, probably 4.5 tonnes, so more than enough, possibly 9x more than necessary. I know not from formulas, but from experience, that it will hold fine on 3:1 in 40 knots of wind.

To put it another way, my anchor has more holding power at 3:1, than a Delta anchor of the same size has on 10:1, or than the same anchor, one size smaller, has on 10:1. Scope by itself doesn't tell you anything; it is simplistic and silly to make a fetish out of it. What anchor do you have? What size? Then we can talk about scope.

If you have an undersized CQR, of course, YMMV.