Anchor dragging...

[kingsebi]

Sorry to start another anchor thread. I have been reading lots of them and thought I was doing fine. Until now the anchor always held with winds up to 30kn plus gusts. I'm puzzled as to what happened today. Maybe someone can help me, I try to be as specific as I can.

Anchored in a protected bay. Bottom mud. Forecasted 35kn with gusts 45kn. Rocna 20kg anchor on 40m of 10mm chain in 4m deep. Supposedly well set after 20-30kn the other day. 5m snubber of 20mm three strand polyester. Boat is 11m and weighs 6tons.

Any ideas as to why it did drag? I'm thinking not enough snubber line or wrong material? Or something I have never read about: I did not lash down the wheel as I normally do if they forecast high winds. Could this have made the boat turn into the wind and break the anchor free? As soon as the anchor broke loose the boat made a full circle before I centered the wheel and motored into the wind.

I live on the boat year round and really would like to get back my confidence in my anchor setup, as this is an important part of this life.

 

[Whitlock]

If it was well dug in and then broke out something tripped it. It would help if you could say over what timescale i.e. overnight? Were you asleep and didn't notice any change in the boat's position?

 

[Poey50]

There's always the possibility of bad luck - something preventing the anchor from setting properly then letting go as the boat veered.

But what kind of mud? Soft, sticky, sandy? Was there a change of tide / wind direction that might have required a reset? (Noting what you said about the "full circle".) There are some concerns (hotly contested) that in a certain consistency of sticky mud the flukes on a Rocna can retain mud and prevent a reset. It's been demonstrated at shorter scope but you had plenty out by the sound of it.

 

[CJ13]

It probably wouldn’t have caused you to drag but IMHO your snubber is to bigger diameter. 20mm dia will have minimal elasticity. I have a 12m x 8 tonne boat and use 10mm 3 stand set up as a bridal.

 

[Tim Good]

When you drop your anchor are you moving astern to ensure the anchor and chain and laid down as you go? I see a lot of people letting their anchor and chain go whilst stationery which can lead to it bunching on top of each other and potentially causing it to knot up and set weirdly.

Possible also you got a big bit of hard mud stuck in it in amongst soft?

But if if was set well with a good deal of reverse initially then difficult to say why it would drag subsequently.

 

[Boathook]

I suspect that your snubber is too short and too bigger diameter. Neeves who lives in Australia will be along later and will recommend a 20 plus meter snubber of 10 or 12mm rope. I do suspect though that you were just unlucky with dragging, but lucky that you were on board at the time.

 

[kingsebi]

Thanks for the answers.

Whitlock: Wind went up at 6am. I was awake and monitored the boats position on the GPS. The anchor held fine until around 8am. No change in wind direction and no tide. The wind was increasing but not alot. It was very gusty all the time. When I saw the boat moving on the GPS I jumped out of bed and into the cockpit.

Poey50: Sticky mud, exactly. The wind from the North all the time. What I meant was, as soon as the anchor broke free the boat got broadside into the wind and then running with the wind, until I turned the wheel to get the bow back into the wind. While this happened the boat dragged fast, around a 100m, what coincides with what you say about the Rocna in mud.

Jfowler: Thanks for the input. I was reading threads about snubbers just yesterday and I will change it for a nylon one and longer. I think the snatch load of the waves could have pulled out the anchor.

northcave: When I set my anchor I always go in reverse until I feel that the anchor has set. The anchor had held fine through 20-30kn winds the other day and also for the first 2 hours of today. All same wind direction. If there is mud in the anchor I don't know, I cut the rope that holds the chain in the anchor locker and dropped it with a line and a fender. Was very hard to pull it all up by hand in these conditions. I will go and get it next week.

Boathook: I read what Neeves wrote about snubbers on this forum yesterday. I think I will follow his advice to get a long one. My reference up to date was Skip Novaks storm anchoring techniques where he deploys a short fat snubber. As this was used around Cap Horn I thought it should be good for the Med. I really don't like the idea that I was just unlucky. I'd prefer to improve my anchoring and have confidence. I mean the weather was not that bad after all.

 

[Tim Good]

Are you using a decent anchor alarm app?

 

[kingsebi]

I'm using the navionics app and always make a track when it blows, like that I can see well if the boat is only veering or if the anchor is dragging. I also look out and take transits. I thought I was quite prudent.

 

[Quandary]

The snubber certainly will no be doing much as it is the wrong material and too thick to have any real elasticity, but a a 20 kg. Rocna on 10mm chain with a scope of 1-10 should still have held. The only thing I would change would be to use something with a fair bit of stretch like 14mm. nylon. There are folk here better placed than me to comment, I try to find somewhere secure if 20kts is forecast.
Jeez! what am I doing here in an anchor thread

 

[Tim Good]

I'm using the navionics app and always make a track when it blows, like that I can see well if the boat is only veering or if the anchor is dragging. I also look out and take transits. I thought I was quite prudent.

I don’t believe the navionics app will alert you if you go out of zone or drag?

 

[kingsebi]

Thanks for the advice Quandary. I will certainly change my snubber setup. I thought this place was secure. Maybe I was pushing it too far. I wanted to have a reference point, to know that my anchor will hold in a storm. Not alot of success with that.

northcave: You are right, it doesn't alert you, but I watch it all the time when it blows. I'm new to life on the sea and as I see these great forces I try to be prudent. The problem I have with the anchor alarm is that when I deploy the anchor from the bow I have to press a button to mark the position. Being singlehanded this seems difficult to me. Either I have to bring the phone to the bow where i will probably drop it, or I press the button when I'm back in the cockpit and will not have the right position and the anchor alarm would not make alot of sense. Sorry to be so complicated and maybe I'm being too perfectionist. I'm still wrestling with my german heritage.

 

[NormanS]

Unless you were anchored somewhere with big waves (unlikely), with a scope of 1:10, I don't see that a snubber, or the thickness or material of the snubber, is at all relevant. I was going to ask what was on the anchor when it came up, but I see that you slipped it and plan to retrieve it later. I can only suggest that your anchor has fouled something on the bottom, a patch of weed, or some discarded rubbish perhaps. I have been unlucky enough for an anchor fluke to catch in a discarded tin can. ? See what, if anything, comes up on the anchor, and you may have an answer, but I always say that anchoring is an inexact science. There are too many variables.

 

[Poey50]

Poey50: Sticky mud, exactly. The wind from the North all the time. What I meant was, as soon as the anchor broke free the boat got broadside into the wind and then running with the wind, until I turned the wheel to get the bow back into the wind. While this happened the boat dragged fast, around a 100m, what coincides with what you say about the Rocna in mud.

Don't get too alarmed by this video - he is testing re-set at shorter scope than would be usual and at higher speed. Nevertheless it may help to suggest more caution in sticky seabeds if perhaps a reset is anticipated. Limitations on a straight pull (again at shorter scope than usual) are also discussed in relation to this seabed.

 

[noelex]

That is certainly a disappointing performance and I can understand why your confidence is shaken. Your snubber does not have enough stretch and this would not help. The wheel position normally does not have much impact, as unless there is a significant tidal stream there is little fore/aft water flow to produce any force when at anchor.

Mud normally provides excellent holding unless it is exceptionally thin and watery, and most anchor designs work at least reasonably well.

It does not take much anchor performance to hold in 20-30 knot winds. It is possible that the anchor was fouled or caught on debris. Items of clothing or towels (probably blown off guardrails when hung up to dry), as well as man made rubbish are a depressingly common sight on seabeds. Also, areas of isolated rock are not as rare as people imagine.

It is important to have good equipment and a sound technique, but anchoring is never 100% reliable.

This pair of shorts (with a rather unfortunate peg ) was photographed not far from my anchor.

 

[LadyInBed]

Could well be just bad luck. I once hooked into a discarded crab pot!

 

[vyv_cox]

Could well be just bad luck. I once hooked into a discarded crab pot!

Indeed, seems like a strong possibility. Over the years I have hooked a tin can, perfectly placed on the tip of a Delta, a huge bundle of monofilament fishing line that only just fitted into a black bin liner and a large boulder that came up with the Rocna.

 

[TernVI]

Is the boat jerking the chain?
If so, then you'd suspect a better snubber might help.
Other wise it could just be you've hooked some rubbish on the seabed preventing the anchor burying.
Or the anchor has got broken or bent. Or Disconnected!
Some anchors it's possible to foul, by dumping some chain over it, not sure that's possible with a Rocna?

Sounds like the anchor actually broke out of the seabed and dragged freely over it, not digging in at all, not even enough drag to keep the boat head to wind, which sounds like catching rubbish on the seabed to me? It's funny how anchors can hold for a few hours, maybe being dragged a few metres, then it all goes suddenly bad. Been there, it came up with a length of angle iron and a bit of fishing net.

 

[GHA]

Thanks for the advice Quandary. I will certainly change my snubber setup. I thought this place was secure. Maybe I was pushing it too far. I wanted to have a reference point, to know that my anchor will hold in a storm. Not alot of success with that.

northcave: You are right, it doesn't alert you, but I watch it all the time when it blows. I'm new to life on the sea and as I see these great forces I try to be prudent. The problem I have with the anchor alarm is that when I deploy the anchor from the bow I have to press a button to mark the position. Being singlehanded this seems difficult to me. Either I have to bring the phone to the bow where i will probably drop it, or I press the button when I'm back in the cockpit and will not have the right position and the anchor alarm would not make alot of sense. Sorry to be so complicated and maybe I'm being too perfectionist. I'm still wrestling with my german heritage.

The anchor android app lets you set the hook position afterwards, easy to do and I have it on all the time on the hook, great little piece of software.

As for snubber, after a lot of research I went for 10m of 10mm nylon on a 10t boat. Seems too small but that's what the numbers say.

But don't loose faith in the rocna, they are very good - was there much mud or rubbish on it when it came up? I've had a spade drag easily just with a small bit if cloth caught on the tip before.

As for setting the hook - I'm up near full revs backwards for a good half minute or more and watch the transits stay perfectly in line - then relax

 

[kingsebi]

When you drop your anchor are you moving astern to ensure the anchor and chain and laid down as you go? I see a lot of people letting their anchor and chain go whilst stationery which can lead to it bunching on top of each other and potentially causing it to knot up and set weirdly.

I reread your post and now I understand better what you mean. I don't think this was the problem as the anchor held fine for two hours and the wind was already up, but I will take extra care in the future. I usually turn into the wind before anchoring, let the boat come to a stop, drop the anchor and pay out the chain that I have flaked out on the foredeck, then go back to the cockpit and reverse until I feel the anchor has set and the boat is swinging, then rev up a little and cut the motor. I see that this could lead to the problem you describe, when it's calm and the boat is moving backwards slowly.

NormanS: No big waves, that's why I choose the spot. 1-1,5m at the most. I will see what comes up with the anchor. Maybe I really caught something.

Poey50: Thanks, interesting video. Maybe another anchor would be better for mud. A Fortress for example.

noelex: Thanks for the insights. I'm looking forward to retrieve the anchor as soon as the wind has calmed down. Maybe that's the explanation after all. Haha, the peg.

Ladyinbed and vyv_cox: That would give me my confidence back in the Rocna, which has until now served me very will, but I wonder what one could do about the anchor catching things on the seabed. In summer I snorkel over the anchor to be sure. Maybe I should get a neoprene suit for winter.

Is the boat jerking the chain?
If so, then you'd suspect a better snubber might help.
Other wise it could just be you've hooked some rubbish on the seabed preventing the anchor burying.
Or the anchor has got broken or bent. Or Disconnected!
Some anchors it's possible to foul, by dumping some chain over it, not sure that's possible with a Rocna?

Sounds like the anchor actually broke out of the seabed and dragged freely over it, not digging in at all, not even enough drag to keep the boat head to wind, which sounds like catching rubbish on the seabed to me? It's funny how anchors can hold for a few hours, maybe being dragged a few metres, then it all goes suddenly bad. Been there, it came up with a length of angle iron and a bit of fishing net.

Yes that was my impression. Moving freely over the seabed. What you say might be funny but it's also scary. I will go for a longer snubber to better absorb the snatch loads, I think that could have been part in breaking the anchor out.

GHA: I will check out the app. That sounds like a solution. For the snubber I thought the same thing. Even the 20mm rope looked too thin to me. For the rocna I will see next week. I have been very happy with it until now, as going in reverse I can feel it set and it mostly sets instantly. Except one other time in mud I couldn't get it in. Maybe get a Fortress for the mud and as a kedge. What you say about setting the anchor is what I do. Go astern and watch transits, feel the chain taut and the boat swinging.