Anchoring in Mud

[MarcW]

We use a Manson Supreme with not issue in mud, rock, sand but weed can be a issue.

Has been used, Geraldton WA to Tasmania over the last 8 months.

Very happy with our 15 kilo Manson Supreme , 67m of 8mm chain and 6 tonne yacht.

[svstrider]

(Apologies - a bit long)
I had not ever come across the term "soak time" I must remember it for future breeze shooting events with other cruisers.

We have a 22 kgs Rocna on our 8tonne cat which has LOTS of windage (think block of flats). I have sailed Sydney to Lizard Island in North Qld 5 times without mud problems apart from Airlie Beach.

For a lot of reasons, the Admiral refers to it as Airlie Bitch. Might have something to do with the toxic mud, crowded exposed anchorage in northerlies and all the young back packers that get my attention and, oh yeah, the pubs full of the former.

When anchoring in mud, I try and use the windage of the boat and all the wind that has been very evident in Oz the last year, rather than hard backing down to set my Rocna in soft mud. The only time Pelican has dragged this season was up in the Duke Islands when I foolishly anchored off an area of the beach where you could see a hard sandstone shelf going out into the water rather than further up where the beach was sandy.

At the usual bewitching hour of 0300 hrs I was awoken by added movement of the boat (another plus for insomnia) and found we were dragging quite quickly offshore in 30 metres of water with another island and reef on our lee.

It was "a dark and stormy night" (also no moon) and was forced to reanchor using the chart plotter. This time down the beach but parallel to my marked anchoring point. IMO it is always a good idea to mark where you drop the pick even if you delete it the next day. You can keep it for future trips if it turns out good holding.

This is the third time that having a chart plotter has saved my bacon, since I bought it a year ago. If I had to depend on the old hand held GPS that I had used for the previous five years, I would have had to head out to sea, dodging lots of reefs in the pitch black, and wait for the sunrise.

I think the only anchot that would have held in shallow sand over a flat compressed sediment bottom would have been an old style Admiralty anchor.

[Mark Johnson]

Our 35# Delta has held us through thousands of nights on the hook and hundreds of gale force winds.

The trick in really soft mud, assuming there is denser mud or sand underneath, is to work it in slowly. The Chesapeake is bad about soft mud! Using 7/1 scope... We back down a bit to get a feel for the holding. If is seems to slip more than a foot or two, bring it back up and clean it off. Then deploy it again and let her sit in reverse, just above idle, for about 20 minuses. (Just chill and have a beer). Then up the RPMs slowly to about 1/3rd, and again let it run for 10 minutes or so. Eventually you should be able to really throttle up, once you have wiggled it below the soft mud! It just takes patience Grasshopper!

Our 34' Tri has a folding prop and 18 HP engine, so we shoot for FULL RPM in reverse, before I can sleep soundly. For us, this equates to > 60 knots of wind!

Everyone should learn how much reverse RPM = how much wind. (more or less), and anchor for a gale every night. Unless the soft mud is a layer on top of hardpan, or a really loose gravelly bottom, it is almost always possible.

Mark

[callmecrazy]

Originally Posted by Mark Johnson

Our 34' Tri has a folding prop and 18 HP engine, so we shoot for FULL RPM in reverse, before I can sleep soundly. For us, this equates to > 60 knots of wind!

Everyone should learn how much reverse RPM = how much wind. (more or less), and anchor for a gale every night. Unless the soft mud is a layer on top of hardpan, or a really loose gravelly bottom, it is almost always possible.

Mark

I was taught the same thing, but was simply told what rpm to use... so, how do you actually calculate it?

[Ram]

Originally Posted by Mark Johnson

Our 35# Delta has held us through thousands of nights on the hook and hundreds of gale force winds.

The trick in really soft mud, assuming there is denser mud or sand underneath, is to work it in slowly. The Chesapeake is bad about soft mud! Using 7/1 scope... We back down a bit to get a feel for the holding. If is seems to slip more than a foot or two, bring it back up and clean it off. Then deploy it again and let her sit in reverse, just above idle, for about 20 minuses. (Just chill and have a beer). Then up the RPMs slowly to about 1/3rd, and again let it run for 10 minutes or so. Eventually you should be able to really throttle up, once you have wiggled it below the soft mud! It just takes patience Grasshopper!

Our 34' Tri has a folding prop and 18 HP engine, so we shoot for FULL RPM in reverse, before I can sleep soundly. For us, this equates to > 60 knots of wind!

Everyone should learn how much reverse RPM = how much wind. (more or less), and anchor for a gale every night. Unless the soft mud is a layer on top of hardpan, or a really loose gravelly bottom, it is almost always possible.

Mark

How do I figure this out?

[Cavalier]

Originally Posted by callmecrazy

I was taught the same thing, but was simply told what rpm to use... so, how do you actually calculate it?

When considering hull form, prop geometry, chain weight and topside windage amongst other variables in such a calculation it would not be straight forward applying some form of generic formula to this problem.

One method, and I'm sure there are going to be many other simpler suggestions, is to borrow/rent a fish-weight (250lb+ scale newton spring) or load-cell (tension type) for a while. Firstly, run your anchor chain through your anchor roller to the dock or fixed mooring with the load cell or fish weight connected into the chain via a shortened bridal between two links - so that under tension all load goes through the scale/cell but if the unit fails then the 'slack' section of chain going around the scale/cell will become taught again. Then run at 1250 rpm in reverse and note the load on the scale/cell. Do the same at 2500rpm noting the scale/load. As 0rpm should equal zero load, you'll now have enough points to assemble a simple curve on a piece of graph paper (or excel etc). You'll now have bollard-pull characteristics specifically for your vessel (albeit in reverse!)

To establish the true effect on the anchor holding ability of windage on your hull and topsides and current on your hull, keel, rudder. You'll need to put together a similar arrangement on your chain just outboard of the roller after you've set anchor an are expecting a windy evening (not due to gastric issues). At varying wind speeds the load on the scale/cell can be monitored to form another graph, which can be compared against the bollard-pull data.

You'll then have a direct translation between RPM in reverse (when setting anchor) and the at which windspeed you know you're most probably safe until. For example, setting at 2500rpm gives me holding up to 45knots...

[Mark Johnson]

In my case it is much more experience, with a bit of guess work, than science. I know that with our relatively low windage, and the fact that the bridle keeps the bows pointing dead into the wind, with no sawing around, gives us a lower pull value on the anchor than many classic books generalize about.

As an example, If I sit on the bow deck and really plant my feet on the bow rail legs, using my entire torso, I can pull the boat forward a foot (and hold it), in 35 knots of wind. The most that I can imagine pulling this way is about 300#s, so this is a starting point.

On a calm day, I have my wife throttle up in reverse, until I can't even come close to holding it in the above fashion. I know that this much pull (or RPM) is equal to over 40 knots of wind.

I take into account the % of RPM left, = about how much more reverse thrust is available, figure in the fact that the wind induced drag on the boat is the cube of the wind velocity, and shake it up well...

No really... Mostly, above the RPM # that I know = 40 knots of wind, which I got with experimentation, I just go by experience. In thousands of nights on the hook, I have never dragged an inch if I previously backed down at 3,400 RPM. At this RPM, the pull on my chain is such that the chain is straight, and I can walk out on it a bit. (Holding onto the bow rail)

I haven't kept count, but I believe that the number of short intense 60 knot + thunderstorms I have ridden out safely this way, is well over 100 times. Then there was the dozen or so hurricanes, in which I really have no idea what wind speed the anchor encountered, because I spread out the load, and sought good shelter.

For you monohull guys with big engines and big fixed props, it may be that HALF throttle for you is = 60 knots. Doing some math, the above experiments, and lots of experience, should get you in the ball park. FOR SURE, your chain should be BAR tight and mostly straight!

One thing I have observed for decades, all over the Gulf of Mexico, Keys, US East Coast, Chesapeake, and both sides of the Caribbean, is this: 90 something % of the cruisers I've seen, use too short a scope, and don't back down NEARLY enough to know if they are good for even a 30 knot blow in the middle of the night. They back down just enough to straighten out the chain from snaking on the bottom, and if it stops the boat, with NO further throttling up at all, they shut it down. This is not comforting, especially if they are in front of me. As to you other 10% THANK YOU!

Hope this is of use... Mark

[Teeto]

Many thanks to all the fantastic replies. I think the "settling time", or lack of was our issue. We are up in Morton Bay where conditions are very murky at the moment. We do have a CQR as a second anchor with chain and a Danforth as a third, so if we have problems in the future we'll swap over from the Supreme, or anchor in tandem. Love this forum!

[boatman61]

AHhhhhhh..... "Brucie Baby....."

[markpierce]

After a many pinched finger and hauling up lots of mud, I avoid danforth types. I Bruce-type works handily in mud and avoids such irritations.

[noelex 77]

Originally Posted by Mark Johnson

Our 34' Tri has a folding prop and 18 HP engine, so we shoot for FULL RPM in reverse, before I can sleep soundly. For us, this equates to > 60 knots of wind!

I think this might be a bit optimistic. Conventional wisdom is that a sailboats engine is unlikely to apply more force than around 25K of wind.
I always back down hard on my anchor (with a Maxprop that has good thrust in reverse), but I have noticed on numerous occasions the anchor will bury more than I can achieve with the motor alone once the wind gets above 30-35K.
This implies to me that my setting is only the equal of this sort of wind speed.

[womensetsail]

We use a danforth here in the soft sand in SW Florida as well. Sometimes I think the sand is worse than mud.

[Mark Johnson]

Noelex,
This may be true for your boat if your boat's size, windage, OR "monohull sawing around" is high, relative to the engine's available reverse thrust. Only you could know the answer to this... My statement about OTHER than my own boat, was based on this:

I have been told by many monohull sailors that their reverse thrust, at full RPM, is more than their working anchor could EVER hold, even in great holding, then we would get 60 knots that night, and they would hold just fine! Only these observations lead me to believe that what works for them might work for most, but perhaps not all. BTW... I have never met or seen a > 35' monohull cruiser, with a powerful engine and good reverse thrust prop, that backs down at even 3/4 of max RPM., much less FULL reverse throttle! I may be wrong about this, but most of my cruising friends are monohull sailors, many have been around the world or the equivalent, and they have all told me the above answer, when I asked: "When there are storms around, why don't you set the hook at FULL reverse RPM"? It is definitely not "etched in stone", however.

Not intending to get into the pros & cons of one type of boat VS another, but...

As I said in a previous post, my case is different. The various "anchoring bibles" put the stress on my rode, in 40 knots of wind, at SEVERAL TIMES what they really are. I am sure of this...

A similar size monohull to mine, (34'), raises the bow in the chop much higher and being heavier, has much more inertia, than my boat. Most importantly, monohulls saw around from side to side, and when in the "sailing sideways" phase of sawing around, they present more windage, and experience multiples of the straight on load. In really high winds, the anchor is also being worked from side to side, loosening its grip on the bottom.

Where as my anchor rode load stays constant, if the wind and waves do, the boat sawing around has its load vary several hundred %, even with a steady wind!

Since I use a 30' long bridle that is 21' wide, and it attaches to the chain with a rolling hitch, 30' in front of the boat, it points straight into the wind, and doesn't saw around. NOT even a foot! This makes the load on my rode during a gale, in the neighborhood of 1/3rd that of a similar sized monohull.

As I said in my earlier post, I can pull my boat forward a foot or two, in 35 to 40 knots of wind! When I do this, the bridle goes slack, and my trimaran DOES want to "SAW". As soon as it gets just 5 degrees from its normal STRAIGHT ON orientation, it takes the rode right out of my hands!

This "low windage trimaran" advantage doesn't necessarily apply to large multihulls with HUGE cabins, like topheavy luxury catamarans. Their bridles work the same, but the huge amount of windage, compaired to a monohull, becomes more of a disadvantage, than the bridle is an advantage.

My point was simply to suggest that we all figure out how much reverse RPM = say... the 60 knots of wind that is common in a summer thunderstorm, and always set the hook for that possibility. If ones engine / prop combination can't achieve that much thrust, then using good scope, selecting the best bottom you can, and eventually work up to giving her all she's got, is the best you can do.

ALSO... In clear, <35' water, like the Bahamas, I always free dive on the hook, (unless its dark)
I have used my "viewing bucket" and seen that the anchor was sitting pretty, only to find after diving, that the hook was sitting in only 8 or 9" of sand, on top of a solid sheet of hardpan. In this case the tip of the anchor was hooked on a ledge, and my previously achieving full reverse RPM without dragging, as well as it looking fine from the "viewing bucket", was a deception! If we had gotten just 25 knots, from a different direction, she would surely be moving on!

May we all wake up where we went to sleep!
Mark






Mark

[Mark Johnson]

I'm sure that most of you know this, but:

One note that I forgot to mention... I use a Delta 35, BY ITSELF, as my normally used working anchor. (95% of the time). I may upgrade to a Rocna someday? ANY anchor used by itself, = (not opposed by another anchor in the opposite direction), AKA "Bahamian moor", should be a plow design. The Bruce and CQR have to be much heavier than the newer designs, like Delta and Rocna, for the same holding power, but if appropriately sized, they are fine. ALL 3 of my EXTRA anchors are increasingly larger Fortresses, with two of them partially dissembled. I have made moorings with these together, that endured 150 MPH gusts in Hurricane Ivan!

NO Danforth, Fortress, AKA "lightweight" style anchor, is intended to be used by itself, except as a temporary storm anchor where wind is from one direction, and strong enough that it will definitely overcome the current.

On a VERY rare perfectly clean sand bottom, with NO shells, beer cans, or anything else, they will reverse, flip flop at the hinge, and reset as designed, in the opposite direction.

This is in these rare perfect bottom conditions only. In thick ICW mud, they will not flip at the hinge with the reversing current, and once drug about 10' in thin but really sticky mud, they are clogged up, and need to be retrieved and the mud removed, before they will reset! On sandy bottoms, any chunk of debris, even golf ball sized chunks of organic matter, will keep the anchor from flipping as designed. (lighter anchors are more vulnerable than the huge 80# ones)

I spent years on the hook in Key West, anchored out 2 miles, and spent thousands of hours snorkeling around my boat. On average, there was piece of "something" that would clog the hinge of a Danforth, about every 5'! The same has been true in the Bahamas, as well as both sides of the Caribbean.

My largest fortress has 4X the holding power of my Delta, but for overnight anchoring on one hook, like most of us do... Reliability on reversal is FAR more important than max. holding power... IF your plow is large enough and well set!

My thousands of nights on the hook, lead me to this guesstimate: The odds of my single Delta resetting itself in a really strong, sudden reversal of wind, like in approaching thunderstorms, is maybe 30 to 1 FOR successfully "re-setting". I would give the odds of my Fortress, (used by itself), in the exact same scenario, as about a 50 / 50 chance of re-setting itself in time. They're great "storm" or "secondary" anchors, but NOT designed for a reversing load, or to be used by themselves where this is likely!

This is why most everyone uses the plow types when laying to one hook, in spite of far lower holding, pound for pound...

Mark

[craigsmith]

Originally Posted by Mark Johnson

My thousands of nights on the hook, lead me to this guesstimate: The odds of my single Delta resetting itself in a really strong, sudden reversal of wind, like in approaching thunderstorms, is maybe 30 to 1 FOR successfully "re-setting". I would give the odds of my Fortress, (used by itself), in the exact same scenario, as about a 50 / 50 chance of re-setting itself in time. They're great "storm" or "secondary" anchors, but NOT designed for a reversing load, or to be used by themselves where this is likely!

You're absolutely right, but please stop calling a Rocna and every other anchor that's not a plow, a plow

Originally Posted by Teeto

Many thanks to all the fantastic replies. I think the "settling time", or lack of was our issue. We are up in Morton Bay where conditions are very murky at the moment. We do have a CQR as a second anchor with chain and a Danforth as a third, so if we have problems in the future we'll swap over from the Supreme, or anchor in tandem. Love this forum!

The CQR will be a lot worse than anything else. Unless it's a lot heavier. The Danforth is not appropriate as a primary anchor. You can't easily rig any of your anchors in tandem as none of them have appropriate attachment points, you would have to rig to the rode, and I wouldn't trust any of them to behave in any manner I would want.

I would make some comment about using a knock-off instead of the genuine thing, and how you would likely see a difference, but I suppose it goes without saying. In mud the fluke-to-shank angle is as important for holding power as it is for setting behavior in hard stuff - you can help by maximizing scope - but if it's mucked up slightly, as imitators are wont to do in ignorance of the original design, it's easy to screw up the anchor's performance. That's why the likes of Fortress have adjustable fluke angles for mud - too hard to make Danforths work well in both hard and soft with fixed geometry. Secondly, Manson's version of the fluke is a simple 2D stamped curve (roll), which results in steep sidewalls toward the rear of the fluke and a flat center; this gives very compromised behavior of mud over the fluke and reduced holding for the same surface area.

It should still not be completely useless. If you continue to have problems, maybe you have a lemon - complete failure to set and hold in mud could be down to the shank not mounted in the correct location, or cut to the wrong angle, or fluke distorted, etc.