Dragging a Delta.

[DJE]

A couple of years ago I replaced a rusting 25lb Sowester Plough anchor (CQR copy) with a 10kg Delta. Generally I've been very happy with the new anchor except for one spot at Shipstall Point in Poole (behind Long Island). We anchored there many times with the old anchor in all sorts of weather and it always held firmly and sometimes dug in so deep that it was difficult to break out.
Since we changed anchors our favourite spot has been taken by new moorings so we have to anchor a bit further upstream. Last year we tried to anchor there in strong winds with the Delta; it seemed to set but then slowly and continuously dragged. We went back on Saturday and tried again and all seemed well when we went to bed but we woke up at low water on the mud at the edge of the channel. We had dragged about 100m and luckily missed another boat and a channel marker post. Bilge keels so no harm done but just wondering why we should have trouble at that one spot. The bottom as far as I know is soft mud. The water is no more than 3m deep at HW and we generally lay out about 20m of chain.

 

[Seajet]

On the basis that there's no such thing as coincidences, I'd check the change of anchoring position further; if it's soft mud surely you'd be certain of that, as mud would be coming up on the anchor ?

With that depth and amount of scope, I'd expect almost any anchor to hold !

 

[DJE]

You're right soft mud on the anchor - soft to very soft grey silty clay for those of us who've done a bit of soil mechanics!

 

[maby]

We dragged a delta a couple of hundred yards along the Medway a few weeks ago - in deep mud... I suspect that I had not dropped enough chain - we were only stopping for half an hour and I anchored in a hurry - don't currently have any marking on the chain, so we were guessing the amount we had laid. It did surprise me since there was no strong current or wind at the time. I suspect it also surprised the other boats we dragged past while we were fixing a sandwich!

 

[Seajet]

It seems to me there's something funny going on about either the anchor design or, not being rude, the operation of it.

As I say, to drag in those conditions of depth & seabed, I'm wondering if the anchor is ever taking hold & digging in at all, sounds like it isn't and you're lying to the chain !

 

[lustyd]

Could it be that you're dumping the chain too quickly and it's piling up around the anchor and then preventing it from setting?

 

[noelex]

I think the delta is a very good anchor only beater by some of he newer generation anchors. However I have seen it, on several occasions when diving, drag slowly while remaining set. It looks like a worm burrowing under the surface.
This is unusual, normally anchors hold if set and drag when they break out.

It seems to me the Delta sets very well, but offers less resistance than other designs when buried. This is more of a problem with soft substrates.

 

[sailorman]

I think the delta is a very good anchor only beater by some of he newer generation anchors. However I have seen it, on several occasions when diving, drag slowly while remaining set. It looks like a worm burrowing under the surface.
This is unusual, normally anchors hold if set and drag when they break out.

It seems to me the Delta sets very well, but offers less resistance than other designs when buried. This is more of a problem with soft substrates.

So my Belgian Bruce is better then

 

[Sans Bateau]

I've held three boats on my Delta at East Head against an ebb tide, recovering the anchor was the difficult bit. The only place I have ever dragged was in Newtown creek, a ploughed field sea bed.

So knowing the OP's sailing CV and the performance of the Delta, I'd say the sea bed in the chosen spot is a soft mud soup.

 

[jimi]

The only place I have ever dragged was in Newtown creek, a ploughed field sea bed.

Same here, subsequently when anchoring in mud with the delta I dumped it and let it sink into the mud and ran out lots of chain then straightened out the chain very slowly. Trying to dig it in quickly with a big burst of reverse did'nt work until the anchor had time to sink through the mud.

 

[ribrage]

silt

A couple of years ago I replaced a rusting 25lb Sowester Plough anchor (CQR copy) with a 10kg Delta. Generally I've been very happy with the new anchor except for one spot at Shipstall Point in Poole (behind Long Island). We anchored there many times with the old anchor in all sorts of weather and it always held firmly and sometimes dug in so deep that it was difficult to break out.
Since we changed anchors our favourite spot has been taken by new moorings so we have to anchor a bit further upstream. Last year we tried to anchor there in strong winds with the Delta; it seemed to set but then slowly and continuously dragged. We went back on Saturday and tried again and all seemed well when we went to bed but we woke up at low water on the mud at the edge of the channel. We had dragged about 100m and luckily missed another boat and a channel marker post. Bilge keels so no harm done but just wondering why we should have trouble at that one spot. The bottom as far as I know is soft mud. The water is no more than 3m deep at HW and we generally lay out about 20m of chain.

Ive spent alot of time working around shipstal point - including wading around the place at mega low water, the top surface of the sea bed is VERY soft primevil, stinking ooze that nothing would hold on, and then its a gravel bottom that is like marbles that would probably be difficult to penetrate ? ?
so maybe your anchor is sitting in the silt and not going beyond it, hence holding in benign conditions but dragging when it picks up - just a thought - im sure someone will be along shortly to disagree

 

[maby]

It seems to me there's something funny going on about either the anchor design or, not being rude, the operation of it.

As I say, to drag in those conditions of depth & seabed, I'm wondering if the anchor is ever taking hold & digging in at all, sounds like it isn't and you're lying to the chain !

Well, I certainly would not take it as rude in my case - as I said, we dropped anchor quickly and, assuming that the current was near slack, I didn't pay much attention to doing it "properly".

 

[Seajet]

RibRages' description sounds like the answer to the mystery to me !

 

[bluerm166]

anchor dragging

Without knowing the area , could it be that the spot in question has been subject to suction dredging for shellfish recently.When this occurs you can see lines of 'puddles' left on the seabed visible at low tide.These are almost continuous depressions that have subsequently filled with soft material and which it's best to walk round on the firmer undisturbed stuff or risk losing your wellies.In effect for a long period it remains liquified mud.

 

[maby]

While not ruling out the possibility that some of the issues reported were due to the condition of the bottom, we dragged in a well known anchorage and dragged past several other annchored boats that did not seem to have any problems. I just get the impression that the delta can be a bit tempramental - particularly in heavy mud.

 

[starboard]

I helped trial the Delta for the RNLI many moons ago when they were looking for an alternative to the heavy Fisherman's that all lifeboats at that time carried.....the Delta was a great success and as can be seen from looking at most lifeboats now the Delta is always carried as a second anchor.
My own experience on my own yacht and I in general would anchor everywhere I went on the west coast of Scotland is that it is the best anchor around PROVIDING it is dropped onto a good clean sandy bottom ( I held in Soay harbour a few years ago for 3 days as the wind gusted up to 75KTS over a 3 day period.....I think your problem is soft mud...tell me an anchor that would hold well in that type of bottom....maybe a Danforth that has a wide blade surface area but I guess not much else!!

 

[noelex]

I helped trial the Delta for the RNLI many moons ago when they were looking for an alternative to the heavy Fisherman's that all lifeboats at that time carried.....the Delta was a great success and as can be seen from looking at most lifeboats now the Delta is always carried as a second anchor.
My own experience on my own yacht and I in general would anchor everywhere I went on the west coast of Scotland is that it is the best anchor around PROVIDING it is dropped onto a good clean sandy bottom ( I held in Soay harbour a few years ago for 3 days as the wind gusted up to 75KTS over a 3 day period.....I think your problem is soft mud...tell me an anchor that would hold well in that type of bottom....maybe a Danforth that has a wide blade surface area but I guess not much else!!

In very soft substrates blade area is very important. A concave blade design also helps. The subtleties of design and high tip weight that help a anchor penetrate a hard or weedy bottom are much less important.
The new generation anchors have a much larger blade area than there older counterparts which together with the concave surface helps provide resistance in these soft bottoms.
In these conditions my vote would go for a large Fortress on the mud setting ( providing there is no change in direction of pull), but the other new generation anchors, like Rocna and Manson supreme, will do a much better job than the older candidates, like the Delta.
I understand the new Manson Boss has an even larger blade area than other new generation anchors, but there have been no independent reports of its performance.

The Deltas weakness is in soft substraites so many anchors will do better in these conditions, but overall it's still a good anchor. At least it tends to drag slowly in a soft mud or sand. Sizing it larger than recommended helps, particularly with the Delta as you retain the good setting inherent in the design with a lager blade area.

 

[vyv_cox]

Plough anchors, of which Delta is one, will do exactly that if they are pulled hard enough or if the bottom is soft. I used one very successfully for 20 years in largely sand and mud mixtures, but had a serious dragging problem in Vliho Bay in a storm similar to the recent microburst event. The bottom here is very soft mud and the Delta just would not hold. To be fair to it, the wind was up to 50 knots and gusting through 120 degrees.

Despite that, i recently bought one for my little UK boat and still carry the old one as a spare in Greece. An excellent anchor for the money, despite this one limitation.

 

[lustyd]

I'm not convinced that concave shapes make much difference. Surely it just fills with mud then acts the same as a flat surface?

 

[noelex]

Fluid dynamics says the drag from a concave surface is considerably higher than a convex one.
Soft mud is not an entirely fluid media, but its close. Combined with the larger blade area of the new generation anchors, the resistance of the blade area is higher than the older generation anchors in soft media.