Anchoring in Soft Mud

[Dockhead]

I'm lying at anchor off Hill Head in the Solent, single handed, enjoying the solitude of an evening on the water in this season. The sea and sky are so beautiful -- a million shades of gray, except that the sea has this milky green-gray color. It's rather calm and not raining for the first time in a month, and a light N wind is blowing, bringing cold (it was lovely and warm yesterday), but I'm snug as a bug in a rug with the central heating going.

I am perplexed by the fact that I had some of trouble setting the anchor this evening, a rare occurrence with this Spade. I used to criticize my previous anchor, a 55kg Rocna, for being ineffective in the soft mud of the Solent, and here I'm having the very same problem with the Spade.

I am accustomed to the Spade cutting right into the seabed right where I drop it under all circumstances. Of course I back down gradually and work it in, but it almost never budges. Soft mud is an odd case -- the anchor seems to hold at first, but when you get to a certain RPM while backing down, SOG on the plotter starts to go up, distance to your anchor (where you set the cursor, right?) starts to slowly increase, and you know the anchor is not holding. This time I veered a bunch more chain, hoping that it would set better, but no. 0.5 knots SOG -- the anchor just slowly plowing through the mud. Although a calm night was forecast, this wouldn't do, so I pulled the anchor up again.

I was surprised that there was nothing on it -- I was sure it was fouled with something. So did it all over again. This time, I let the anchor rest on the seabed for 10 minutes or so before I started backing down on it. It still didn't seem quite stable, so I took it slow. Before doing the final pull at redline, I veered the whole 100 meters of chain (more than 10:1 scope -- I have the whole wide bay to myself). Finally it seemed to hold ok, although I never got the characteristic arc on the plotter which shows that all motion is at a tangent relative to the anchor, the sure sign that you are really stuck.

I guess it is overkill when it's blowing 5 knots out, but I am single handed and intend to sleep, and when you want to sleep at anchor, there's no such thing as overkill, in my book.

I thought about throwing out the Fortress, which is the superlative instrument in mud, but finally the Spade withstood 5 minutes at 4000 RPM, so I decided that would be unnecessary.

It was a bit of a bother -- I guess I spent an hour faffing around with it, and not a small quantity of diesel fuel.

I guess an anchor with huge flukes like Noelex's Mantus might work better in this. Or maybe I should just avoid these spots near river mouths -- the River Meon has been famous for its silt for centuries

[F51]

We have a 99lb Spade and a Fortress FX55. The Fortress is my preferred anchor for mud. If it is really soft I select the "mud" position for the flukes.

[Hoofsmit]

Evening.... Beautiful to see the stars are still above the Uk, the months been a moist one!
Just a thought, but I had similar problems with a similar scenario on what appeared to be mud on one of the Fal/ Truro tributaries, the strata below the 6 inches of mud was hard slates.
Does the sounder show a density?
I found my cheapy eagle sounder showed a very good definition of hard strata below soft mud, also was excellent with showing weed with a twiddle of the gain.... Might be worth having a scan around to find a deeper holding layer of soft stuff.
Hope I'm not teaching granny to suck eggs, have a good night



Sent from my iPad.......i apologise for the auto corrects !!!

[Dockhead]

Originally Posted by F51

We have a 99lb Spade and a Fortress FX55. The Fortress is my preferred anchor for mud. If it is really soft I select the "mud" position for the flukes.

Exactly the same anchor inventory as mine.

Yes, it may be that I should have thrown out the Fortress.

[Dockhead]

Originally Posted by Hoofsmit

Evening.... Beautiful to see the stars are still above the Uk, the months been a moist one!
Just a thought, but I had similar problems with a similar scenario on what appeared to be mud on one of the Fal/ Truro tributaries, the strata below the 6 inches of mud was hard slates.
Does the sounder show a density?
I found my cheapy eagle sounder showed a very good definition of hard strata below soft mud, also was excellent with showing weed with a twiddle of the gain.... Might be worth having a scan around to find a deeper holding layer of soft stuff.
Hope I'm not teaching granny to suck eggs, have a good night



Sent from my iPad.......i apologise for the auto corrects !!!

Are there stars? The barometer is up, but I hadn't noticed. Must go up on deck and have a look. Stop the presses -- stars visible in UK! Declare a national holiday!

[Hoofsmit]

<<<<< gone to have another look

It might have been Culdrose SAR helicopter on night practice !!!


Sent from my iPad.......i apologise for the auto corrects !!!

[avb3]

Originally Posted by Dockhead

...................
I guess an anchor with huge flukes like Noelex's Mantus might work better in this. Or maybe I should just avoid these spots near river mouths -- the River Meon has been famous for its silt for centuries

I have an appropriately sized Mantus on my smaller boat than yousr, however, frequently need to anchor in mud. To this point, it has not caused me any reason to have concern, and it has set the first time every time, so far. (and occasionally I am on a mooring ball)

[DumnMad]

Hi Dockhead, good verbal picture of a nice evening.

"Or maybe I should just avoid these spots near river mouths -- the River Meon has been famous for its silt for centuries"

Silt is the key word. River silts are well known for their propensity to liquify when disturbed or vibrated. Even if the anchor is well set a decent blow might send vibrations down the chain and liquify the surrounding soil.
The soil is strong until vibrated so the anchor moves slowly liquifying a fresh patch as it moves along.

Your 10:1 would help, having a long length in the mud would dampen the vibrations. A blow in the night could start the dragging again but it should remain quite slow.

It would be interesting to see if a rope rode would do better.

Cheers, Nick

[ranger58sb]

Originally Posted by F51

We have a 99lb Spade and a Fortress FX55. The Fortress is my preferred anchor for mud. If it is really soft I select the "mud" position for the flukes.

Originally Posted by Dockhead

Exactly the same anchor inventory as mine.
Yes, it may be that I should have thrown out the Fortress.

I take it you've seen the Fortress testing results -- here and in the much longer version on trawlerforum -- in soft mud?

-Chris

[Pelagic]

Originally Posted by DumnMad

Silt is the key word. River silts are well known for their propensity to liquify when disturbed or vibrated. Even if the anchor is well set a decent blow might send vibrations down the chain and liquify the surrounding soil.
The soil is strong until vibrated so the anchor moves slowly liquifying a fresh patch as it moves along.

Your 10:1 would help, having a long length in the mud would dampen the vibrations. A blow in the night could start the dragging again but it should remain quite slow.

It would be interesting to see if a rope rode would do better.

Cheers, Nick

Excellent explanation…. I call this kind of soft mud “Slurry” and it is notorious for poor holding.

Used to frequently anchor for weeks in Repulse Bay (HK Island) trying all kinds of tricks at maximum scope with two anchors, hoping ground tackle would hold when the NE wind gusts through the valley.

Nothing really worked and we just set up watches for a controlled drag, when the wind blew.
Two anchors actually made it worse if they dragged and came together causing a tangle.

What minimized the problem was to lay out one, then lower the other at only just over the high tide depth, so it slows down the sheering forces on the main anchor chain.

Helped but did not solve the problem so sorry Dockhead, no solution.

[Moody46CC]

4000 rpm for five minutes and no movement on a gps chartplotter? You're dug in.

Guess you like cold evenings. In 2008 I was living outside London and went down to the Isle of Wight--Cowes--for a lovely weekend. Took the ferry from Southampton. Had the most wonderful time in Cowes and Osborne, but on the way there, was sitting on the bridge of the ferry. Passed a regatta of small sailboats--maybe a hundred. Was 33F degrees and raining. A sunny day in Central Europe in the winter. At the pub--in the snug--in Cowes that night, the wife and I could only say, "they are different." As we used to say when I was in the service, "hard core."

[Dockhead]

Originally Posted by Moody46CC

4000 rpm for five minutes and no movement on a gps chartplotter? You're dug in.

Guess you like cold evenings. In 2008 I was living outside London and went down to the Isle of Wight--Cowes--for a lovely weekend. Took the ferry from Southampton. Had the most wonderful time in Cowes and Osborne, but on the way there, was sitting on the bridge of the ferry. Passed a regatta of small sailboats--maybe a hundred. Was 33F degrees and raining. A sunny day in Central Europe in the winter. At the pub--in the snug--in Cowes that night, the wife and I could only say, "they are different." As we used to say when I was in the service, "hard core."

Well, it's +6 -- don't know what that is in Fahrenheit, but I guess '40's. Positively toasty! We sail in much colder weather than this! Actually, it is magical when the temperature is below freezing -- the air has more weight, and you sail a lot faster in a given wind speed. The water seems to be more viscous. I love sailing in the winter. There's a lot of racing here in the winter -- one of the racing programs is called the Solent Frostbite Series.

Cowes, the Urheimat of yacht racing, is our winter home. I spent last night there. Will take up a monthly berth on 1 December until 1 March.

[zboss]

Originally Posted by Dockhead

Well, it's +6 -- don't know what that is in Fahrenheit, but I guess '40's. Positively toasty! We sail in much colder weather than this! Actually, it is magical when the temperature is below freezing -- the air has more weight, and you sail a lot faster in a given wind speed.

No way hombre... we won't do it! T-Shirts and Flipflops for us buddy!

[HopCar]

My limited experience with anchoring in soft mud has led me to conclude that you want an anchor with as much fluke area as possible.


There are three common types of anchors in favor now, the weighted tip (Spade and Delta), the roll bar (Rocna and Mantus) and the Danforth (Danforth and Fortress).


If you had one of each of these and they all weighed the same (pretend the Fortress was steel) The weighted tip anchor would have the least fluke area because so much of their weight is in the form of ballast in the tip. The roll bar anchors would be next in fluke area. The Danforth style would have the most fluke area.


This is why I think Danforth style anchors do so well in tests in soft mud. It's simple, bigger flukes are harder to pull through the mud.


If I had to anchor in soft mud, and I'd rather not, my first choice would be a Fortress with it's flukes set for mud.


78 deg. F in Miami now. Probably go into the eighties tomorrow.

[DumnMad]

I should add; "Soft mud" is a layman's description of a soil that generally describes softness. "Silt" is a technical term describing soil with a specific range of grain size. Both can pull your shoes off but, when vibrated, silt behaves quite differently to other "muds."
Silt may be able to take steady pull on the anchor, but sent vibrations down the chain and it may be a different story