Anchor slipping

[Tomrob]

Hi, this past weekend we were anchored in 20 mph sustained winds for about 24 hours. Held great. As we went to sleep for the night The wind gusts went up to 30 and 35 mph. At 2am we found ourselves bouncing on the beach. Thankfully it was dead low tide and in about an hour or so we were able to motor out to deeper water and re-anchor. We held for 6 hours and then slipped again about 300’ in 5 minutes.

The tow boat company wouldn’t come out because of the winds.
The other boats all seemed to hold well.

We have a Person 31’ sailboat
30 lb plow anchor with 30’ of 3/8 chain
There was 130’ of rode paid out
The sea bottom was sand and or clay.
Any suggestions or advice would be appreciated.
Thanks Tom

[NewMoon]

What was the depth? How well did you test the set?

If it were me, I'd have more chain, maybe 70-100 feet. I'd also look at a more modern "scoop" anchor like Rocna, Manson Supreme etc.

[Don C L]

If this is a CQR plow, in my experience they need more chain and more scope to hold well. I suspect you may not have had enough scope which is the ratio of the length of of the rode relative to the distance from the height of the bow of the boat to the sea floor. If you had 7 to 1 scope, it should have held. So your 130' (If it was all out) should have been ok if the distance from your deck to the bottom is about 19'. How high is your bow off the water? How deep was the water? If there is any grass or kelp for the anchor to foul on, that too will mean it will not hold. If there was swell in the anchorage causing the bow to pitch, that too can make dragging more likely.

[Uncle Bob]

I would suggest a visit to Steve Goodwin's video's of anchors setting, done from his boat s/v Panope.
I think I can see a new anchor in your future.

[Tomrob]

Depth of 12 to 14’
On the set I held 1800 rpm in reverse for about 30seconds

[Don C L]

Originally Posted by Tomrob

Depth of 12 to 14’
On the set I held 1800 rpm in reverse for about 30seconds

Well that should be plenty of scope and this then begs the question, which plow? But I'd be one to suggest getting a new anchor. I grew up seeing CQRs on almost every bow. But the one time I really put one to the test, it dragged. Following that I used more scope but I didn't sleep well on that boat anymore.

Still, given what you have said, and assuming there was no debris or vegetation fouling the anchor, even an engine block should have held with that scope methinks.

[Tomrob]

I can’t help but wonder why it slipped over 25 to 30 mph winds. Not once but twice in the same day and same anchorage.
Thanks

[Reefmagnet]

All chain rode is problematic to holding if it loses its catenary. We had a similar setup with a name brand plow and it was a chronic dragger. Swapped the anchor out for a Rocna spade and, although it brings up half the seabed when raised, it holds great.

[Don C L]

Another possibility is that you happened to drop your anchor in an area where there is mud or sand over a hard substrate and the anchor was not able to bury itself very deeply. As a result it could hold only up to a certain point before it started dragging over the harder substrate.

[MathiasW]

If you are interested in some mathematical modelling of anchor chain and how much is needed - have a look here:

https://trimaran-san.de/die-kettenku...atiker-ankert/

I am currently spending my corona lockdown time at anchor working on an App to calculate at least the basic setup for now: Anchor chain plus snubber / bridle, with inputs such as water depth, wind strength, seabed slope / angle, windage area of the vessel, weight of the vessel, and basic characteristics of the snubber. So, the combination chain + rode is missing. Perhaps in the future...

The iPhone / iPad app should be out not too long from now, and based on how successful that app is, I may start porting it to Android...

Cheers

Mathias

[DefinitelyMe]

You had enough scope. Other boats were holding so substrate isn't the problem. I (and many others here I'm sure!) recommend investing in a new generation anchor. Rocna, Mantus, Manson, Spade etc. Viking looks pretty good too based on the testing done on s/v Panope.

Check out the thread mentioned above. If you have aspirations to become an anchor geek like me and have a few days to spare there's also an incredibly informative thread called 'photos of anchors setting' done by Noelex. It's an old thread but might still be available.

[Nicholson58]

Still don’t know what type of plow. The CQR was a Scottish adaptation of a farming plow. They took a plow and welded on a shank. That device was designed to pass through earth and turn it over. My CQR did just exactly that. I reviewed many promotional videos, YouTube and forum posts as well as independent testing results. I replaced it with a Rocna. End of problem. There are several modern design anchors that work well. At the time, Rocna was the best deal. The independent testing showed just how bad the CQR was and how very good the modern anchors are. We live aboard in the Caribbean on anchor. I seldom even think about dragging. It just doesn’t happen.

[DanielPerry]

I have heard a CQR will break loose but be dependable to dig back in again, but slip again.. not much use off a lee shore or in a crowd. I know people sometimes scoff at the danforth but in sand and clay.. plus you can get one anywhere for a song and 50-100$

If you decide to try one out, make damn sure it doesnt have a groove in the stock to allow the ring to slide up towards the flukes (tripping the anchor, it for temporary anchoring only). I was on a shore once.. But just last week we had sustained 30 with gusts in the mid 40's (mph) for about 12 hours and although I had two anchors out, I know the danforth didnt drag. Ive been very exposed in great lakes waves multiple times with 200' 3-strand and 30' 3/8 chain on the danforth and no problem, other than I slept face down on the sole with my arms out to wedge myself in and conceded that I may wake up to a 'bump'. I even anchored the entire way from Lake Michigan to Mobile on the rivers in substantial current and never once had a problem. I know they arent the best and perhaps a new anchor is absolutely worth it, a danforth isnt bad to have, though.

[Marathon1150]

We had a CQR appropriately sized on our first boat, a Van de Stadt 34. We sailed this boat in Indonesia and frequently were anchoring in sand over coral. That anchor never held, ever. I would set the anchor, pull hard in reverse, wait, and wait and wait. When all seemed fine I would attend to other things and then notice that we were moving because the anchor was dragging. I have zero faith in that particular plow.

Later on another boat we had a Fortress that was a bit light for the size of the boat, but when it grabbed, it really held on. We replaced that with an oversized Bruce which worked really well and then a Rocna 20 with 3/8" all chain on a 38' (11.5m) boat. It has never failed (fingers crossed).

Ditch the plow - as someone once wrote, plows are made to move through the earth, not grab on to it.

[Jammer]

Originally Posted by Tomrob

Any suggestions or advice would be appreciated.

Get thee a modern anchor
Rocna
Spade
Mantus
Manson supreme



If those will not work for your situation you can get a Fortress which will be lighter and smaller but will not hold in as wide a variety of bottoms and will not reset reliably when the wind changes