anchor size

[Peter]

Boaty question for xmas. Looking at a new anchor for my boat and following on from the various recent articles on anchoring. My question is where does boat weight come into the equation on choosing an anchor, not so bothered on anchor type, but the weight of the anchor. All the “tables” give an anchor size/weight against boat length, not on boat weight. Or boat weight is based on a typical GRP yacht, for a 12m boat around 9-10te. As I sail a heavy weight steel yacht, 14.5 te, 12.5m long, I would like some guidance/help on this issue.
The YW anchoring article gave the Bruce anchor some poor press, is this justified, as this anchor type is possibly my preferred choice.

Peter


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[Twister_Ken]

Gravity

The logic would seem to be that the anchor is there to resist the forces acting to move the boat. Gravity is not one of those forces, unless you want to hang the boat up by the anchor. What the anchor more usually does is resist the force exerted by water on the underwater sections of the boat, and the force exerted by wind on the above water sections. The size and shape of the boat would therefore seem more important than the weight in that a lightly built high freeboard yacht anchored in a gale probably exerts more pull on the anchor than a real heavyweight with lots of weight in the keel and no too much top hamper.

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[Mirelle]

Don't know if this helps much, but (as a CQR man) I would go for a 60lb; my 9 ton displacement 12 metre OA boat had a 35 for years, she now has a 45 and I am happier with it. A 60 can still be handled without much difficulty.

This might be overkill, but you will sleep easier.

Sorry, I have no experience of Bruce anchors.

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[MainlySteam]

We are steel also, 40 foot and 10 T lightship and 12 T all up and have quite alot of windage. We use a 60 lb CQR copy (accurate copy but is weighted in the plough) on 10 mm chain and have never had a problem, including in up to F9.

We carry a spare 60 lb to go on a nylon/chain cable or as a spare, but we never use that cable as it is too much trouble compared to chain. We also carry a 45 lb similar anchor in case of need, but again have never used it for the case of holding problems with the main one - the 60 lb one always works (well so far).

Although I have several friends with Bruce anchors I cannot comment on them as have never used one and don't recall one on any vessel I have ever been involved with (mainly high quality or commercial vessels, so perhaps there is a message in that).

John

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[Gunfleet]

<<This might be overkill, but you will sleep easier.>>. He won't. He'll be up all night worrying about how he's going to pull 60 lb of anchor and 50lb of chain off the seabed. Unless he has a whopping great big old gaffer with a whopping great windlass on the front! No wonder you need that extra strength tea, mate

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[AndrewB]

I also have a heavy steel yacht, slightly smaller than yours. My preference is a CQR: a 45lb for sheltered use but a 60lb would be better if you ever anchor in potentially exposed places, leave the yacht on its anchor, or regard your anchor as potentially last-chance salvation on a lee shore. But you will need a decent windlass!

I have owned a 30lb Bruce which, in my experience, is the best anchor on very light holding, like powdered coral. On harder surfaces it sometimes had trouble getting that first grip, and resetting quickly on tide changes.

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[Guest]

Biggest you can handle

For me ..... I don't like the tables of anchor size ..... I always say that the biggest anchor than can be handled on the boat .... the bigger the better.

What makes me say it .... look at the average powerboat with high windage ..... piddly little anchors that I wouldn't use as a lunch hook ..... the windage creates a snatch on it that is out of league with boat size and anchor size. OK so deep draft can be a pull as well ....

So repeated - biggest you can get and fit on the boat.


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[gunnarsilins]

Re: Gravity

But when a boat 'sails' around the anchor, which many do, would not the displacement be a factor t count with? Often you ca nee a boat bare away 30-40 degress from the mean wind direction until the cable goes tight, and the she turns back. Would´nt a heavier boat put more strain to the anchor?

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[Twister_Ken]

Re: Gravity

Yes, it would have more momentum to arrest - 10 tons moving at a knot takes more stopping than 5 tons moving at a knot. And recent anchor tests that I have seen don't seem to have addressed the efficiency of an anchor to an 'off-centre' pull.

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[qsiv]

Re: Gravity

Playing devils advocate - shouldnt the snatch load be attempting to lift the chain off the sea bed rather than tweaking the anchor? If the chain is off the sea bed you have too little chain out for safe holding. I accept that some load will be transferred to the anchor, though.

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[webcraft]

Re: Biggest you can handle

I don't understand the obsession with huge oversized anchors . . . my understanding is that an anchor works by being partially buried in the seabed in a stable configuration, and that surface area and shape are the primary factors once it is set, while weight distribution and shape are the factors that determine ease of setting.

A big lump of steel will not on its own exert enough frictional force to stop you dragging if it isn't set, and I'm not aware of any evidence that heavier anchors are necessarily easier to set.

In addition, a huge wobbly CQR is not exactly easy for a smaller crew member to manoevre round the furling gear and deploy in a hurry or in poor conditions.

Our Vega was equipped with a 15kg CQR on chocks when we got her. It took ages to prepare, occupied most of the foredeck, was almost impossible for my wife to deploy, was a threat to fingers and was IMHO substantially oversized for the boat. It is still on board, but at the bottom of a locker as a 'hurricane hook' for that odd occasion when you might need to deploy multiple anchors to ride out a big blow. It has been replaced on the foredeck by a 10kg Spade, which is much easier to handle and deploy and is more than up to the job.

I think the myth of the massive genuine CQR as the only guarantee of a sound night's sleep bears further examination.

- N





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[Robin]

Re: Biggest you can handle

All things are relative, and what is OK on a 27ft Vega is not the same as on a 40 plus footer, either in terms of loading on the anchor or in stowing and deploying it. In the case of the loading, weight is useful for setting the anchor and surface area may be more important in holding power but increased area = increased weight for the same design. In terms of stowing and deploying, a small boat may well stow it on deck, in a well or in a locker but a bigger boat will most probably stow the anchor in a bow roller and drop/raise it with an electric windlass. The CQR is awkward and finger crunching if lifting on deck around roller stay etc, but much easier if power stowing in the bow roller and with the added convenience of being able to attach a line to pull the head to one side away from No 2 roller for mooring warp.

I see too that you are another one who leaves the little lady to do the heavy & dirty anchor work, I hope my SWMBO appreciates what a nice skipper she has! :0)


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[timevans2000]

Re: Gravity

Lots of good posts but how many variables do we have

boat weight/momentum
windage
under water resistance-if in a strong tide
weight of anchor
weight of chain
surface area of anchor
weight of anchor
length of chain/rope
type of holding

How about height of waves too. This would create its own pull on the anchor as the boat surges up a wave.

It would seem to me that all of the above can be coped with by MORE

More chain/More anchor surface area/More weight of anchor/More scope will all help.
Some people choose to use more of everything some choose to use only one of the above.
We all have differing boats that will only allow certain options.
I have a catamaran so weight is an issue. I chose a bigger anchor made of aluminium. I use a limited amount of heavy chain and the rest is anchorplait.

Somebody with a heavy diplacement, high windage boat would say I was being reckless by not carrying tons of chain and a heavy anchor, but that is because to him it is no issue. To me it would upset the balance of the boat and reduce the sailing performance.

I dont think there is a one size fits all solution



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[Talbot]

Re: Gravity

You left off boat type, as a multihull will perform differently on an anchor to a half boat or a stinkie. You have also left off the most important variable, the type of holding. It is well known that different types of anchor perform differently in different sea beds, hence as you go around the country yoiu will find that local conditions will dictate a favourite anchor for the area. It is for this reason that I have two different type of anchor (delta and danforth)

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[timevans2000]

Re: Gravity

I dont think so. Multihull is covered by windage. I also had type of holding down.

I have 2 different anchors also. One is an aluminium spade the other is a very large aluminium Danforth type anchor. This is relatively light but has huge area and can be dimantled for stowage.

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[charles_reed]

One reason might be..

because windage, which is a factor of size, is the most important single component of the forces exerted by a boat on it's anchor.

You should be aware that the tables published by most manufacturers give the MINIMUM size of anchor far a given length of yacht and for recreational use (ie you won't expect to anchor in an F10).
For that reason it is well to look for a heavier-than-recommended anchor if you intend to live aboard and anchor most nights.
Equally you need to beware oveloading your boat, especially putting weight in the ends.


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