Anchoring in Poor Holding

Last Tuesday we had a strong northerly blowing into the Burnett Heads small boat harbour which was 20 knots constant gusting up to 30 knots.

The holding there is not good with a metre or two of sloppy mud over bed rock. The high tide was just before 2 pm which covers the northern wall of the channel in the river so the fetch was all the way from Lady Musgrave Island about 60 miles north.

Second Wind has been anchored for a couple of months midway between the motor boat and the moored yacht on the right without any dramas in a wide range of wind directions and strengths until this northerly came in.




She dragged her pick right the way across the basin without hitting anything until she grounded at the shore wall.

Two of my mates who live at the marina raced out with a tinnie and nearly stopped her from grounding but a line fouled the prop and she went to the wall. They did manage to get a line from a mooring to my primary winch which stopped her from laying against the wall.

They could not start the engine because I had the main oil line off for repair. They phoned me and I said I would silver solder the oil line and be right down. I felt sick in the guts when I was driving down there but they had her secured with lines and anchors and she wasn't pounding.

We got ourselves organised and set ourselves up to get her off on the next high tide at 2:20 am. Tuesday was right on neaps and the high was 2.11 metres.





It was close but not close enough and we needed 150 to 200 mm more tide to float her so we resigned ourselves to getting her off on the Wednesday afternoon tide at 3:15 which had another 350 mm in it.

Inspection at the low at 9 am revealed that the keel was in a mud hole and the skeg and rudder as you can see was jammed in some rocks. What you can't see is the rock, the turn of the starboard bilge was half an inch off resting on.

I went down and tried to clear the rocks away from the skeg which I was able to do on the bank side but the one on the basin side was too big to budge.

The previous afternoon I fitted the new oil line so that when she came off we would have engine. We had planned to have a 4wd with a winch forward of her on the bank so we could drag her parallel to the bank to get the skeg out of the rocks.

Overnight the wind had changed from NNW to SSW which was very much in our favour.

I got back on board about an hour before the high with my tinnie with an 8 hp donk in case I needed it. We were about to set up the 4wd with winch when much to my relief and with a clap from the guys on the bank she floated off.

The anchor was already out and holding so I started her up and took her over to the marina.

Fortunately the only damages sustained are a couple of scratches from the tinnie on the topsides and the broken self tailer jaws from thrying to winch a knot through it (not by me).


The above story is only to set the scenario for the question about what is the best tackle set up for poor holding ground.

I want to continue using this anchorage as it is quite protected, is little influenced by tidal flows and I have very good friends there who keep a good eye on my yacht. Eventually I will have a mooring up river.

The yacht is a 30 footer with around a 4 tonne displacement and does not have excessive windage. The ground tackle is a 30 lb Manson Plough with 20 metres of 5/16" (8mm) short link chain and 30 metres of 20 mm Kinnears three strand rope.

At the time of the dragging I had 10 metres of chain out in 2 metres of water (5:1 scope) which should have held her in good ground but as I said it is quite sloppy mud in this basin.

First Question:- Should I or should I not have an oversize (say 1/2 inch) swivel between my anchor and chain????? There are arguments for and against. I am interested to hear both.

We have considered tandem anchors in line which can be very good in a blow if you are on board but due to the swinging in the basin and my not being aboard, we have ruled it out. For the same reasons and lack of room we have ruled out having two opposed anchors which will wind up, or fore and aft anchors.

I think the 30 lb Manson is just right for this yacht so I don't want to have a 45 or 60 lb anchor on it.

The next option is a catenery on the chain which could be:-
1. A sliding collar type.
2. A 27 lb plough shackled onto the chain when the main anchor hits the bottom. (Quite do-able but it alters the anchoring dynamic.)
3. Another length (say 5 metres) of heavier chain, shackled at each end and the middle with cable ties between the shackles onto the main anchor chain.

I am in favor of this last option.

Can anybody tell me if and why this would not work or suggest a better way of achieving the desired result of getting better holding in the sloppy bottom????

All moorings there are taken and there is not enough room for 40 metres of scope.

I had 15 metres out the previous time I anchored there and that seemed to be OK. The last time I anchored her we took her out with my tinnie and outboard and didn't get her quite where I wanted and a little close to the motor cruiser with only 10 metres out. Due to peculiarities, it swings differently to the other boats

hey cisco I changed from plow type anchors to a rockna first and loved its holding power and
then I saw the sarca excell at the boat show and did some research on the net we decided
to buy one and the holding power and immediate set in all types of ground is awsome
we are using it with 20 meters of 8mm short link chain and no swivel on our 32 foot seawind cat
anchor is 10kg ,we now use the rockna as our spare cheers ray

Hi Cisco

When you say all the moorings there are taken do you mean that you are not allowed to lay another mooring in the area

Regards Don

how about a 15 kg kellet slid down the rode ?

I wouldnt say a huge improvement but it seems to dig in very fast and will not move
in any type of seabed ,I did notice that the rocna would struggle with a loose rocky
shaley type bottom where the sarca wont hesitate to dig in anywhere ,both anchors
were around the 4 to 500 dollar mark, cheers ray

The Manson Supreme is up there with the best of them. There is a reason for that and if you followed the dramas Rocna had recently with the run of poor quality Chinese steel used in their shanks [ now resolved I think] The Rocna used to be built in NZ and was sold to another company who has the anchors built in China now. The Manson anchors built in NZ apparently designed by a bloke who was involved with the original Rocna.
What anchor is best suited to your vessel is going to depend a lot on where its stowed. A 15 Kilo Rocna or a 15 kilo Spade will not fit in my anchor well and the Spade will not fit easily in a lot of yachts bows. An Ultra will fit my well but the high costs is just too much so I built my own. Previously my yacht had a CQR and they are a plough and in a soft bottom they certainly do. The new generation anchors are generally spade designs and the geometry is almost identical at about 32 degrees I think it is off the top of my head. The size of the spade is about the same and the only real diffrences is in how the anchors self right. Rollbars for Rocnas and Supremes. Weighted blade points and hollow shanks for Spades and Ultras. The secret to rapid securing is the sharpness of the blade edge and point, the angles between the shank and blade are almost identical.
In your case where you want to remain at anchor for some time I would suggest a decent anchor, 8 to 10 metres of10mm chain, swivel then 25mm nylon. Consider a small hard buoy attached to the swivel to keep it clear of the bottom. Piece of poly fire hose around the rope where it passes over your bow. Full chain would need a swivel above the water to stop the chain bunching up as the boat rotates about in tide changes etc. Really chain that is not lying on the bottom is just waste. Really with a good anchor not much chain is needed. My spade copy on my tender is about a kilo and has about 2 feet of chain but for survey or state regs you will need what ever the local regs say, it's usually the boat length in chain.
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This is mine before I filled the bottom section with lead.
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Any advice given here is of course worth exactly what you paid for it.

As an aside, does anyone set anchor trip lines? I am about to come down the WA coast where anchorages are often amongst reefs and rocky outcrops. I am wondering if a trip line would be wise in case the anchor drags under/between a rock shelf etc?

why don't you just throw down the wheel hubs you have, with a length of chain....with a loop of rope. When you move, just cut the loop, remove the rope, and it will sink in to the mud never to be seen again...

Cisco,

As I understand your original post you had 10 m of chain in 2m of water, giving 5:1 scope. My understanding is that you should calculate depth from the sea floor to the bow roller. So if this is one metre above the water the "depth" becomes 3 m and scope around 3:1, which is probably not enough. You had chain and rope out, so why not lay out more chain and less rope?

I cant believe the Great all seeing, All Knowing God of the Seabreeze Sailing forum - CISCO - let his boat drag its anchor in protected waters??
Whats going on There amigo??

I've read about a good idea for you

three anchors in an array 120 degree apart
with chain to a central point
then rope up from there on a swivel

doesn't matter which type of anchor or length of chain but more is good