correct anchor and length of chain for Solent use

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Freebee

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We have a 25 foot Triana power boat weighing about 3.5 tonnes - our surveyor has snagged the anchor which is a Danforth and 5 metres of 8mm chain with a long anchor rope attached. The report says it should be appropriate for the job but does not say what is appropriate. I can't say the size of the present anchor because I am not near the boat right now. Our proposed usage are is probably mostly the Solent.

So my question is what is appropriate equipment for the boat and cruising area???? Is there any official report or spec to support your recommendations???
 
In some Solent locations with a strong current (e.g. East Head), something like 4x depth is needed (if all chain - substantially more if part rope).
Our previous 4000kg boat had 40m of chain, but it had a windlass.
If you are pulling in the chain by hand, that would be far too much weight, so a mix of rope and chain is more usable, but with ultimately less holding power.

Something like 10m of chain with 30m of rope attached would be better than what you currently have, so long as you pick your locations carefully, and I wouldn't want to leave the boat for long or want to sleep overnight anchored. Fine for a lunch stop in Newtown Creek, though :)

I'm sure someone will come along in a minute and start a discussion about the merits of various types of anchors (groan).

http://www.anchoring.com/blog/how-much-anchor-rope-and-chain-do-you-need-for-your-boat/

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whilst unscientific you generally want as much chain, of the largest diameter and as a big an anchor as will fit.

The manufacturers tend to fit the "recommendation" which frequently turns out to be too small for the YBW Forum typical boater!

Ebay can help or your local yard, who may have a pile of them from other boats who were upgrading.
 
When I bought my ferretti 57 I observed that the anchor appeared much too small...... I mentioned as much to the selling broker and he said, Rather wisely with hindsight, " the boat is 12 years old, if the anchor was too small, someone would have changed it". And he was absolutely right, in several years and a huge amount of anchoring I never once had a problem. Don't rush out and buy a bigger newer anchor until you've tried the one that's on there is my advice......

As has already been mentioned it's mostly the chain that holds you in place so lots of it is probably more constructive than a bigger hook at the end of it !
 
When the chain is relatively taught, in a bit of a blow, and even with a bit of a catenary, nothing, other than the anchor, is holding you in place - nothing!
 
Sorry but I can't agree with that.... ... my boat weighed 30 tons..... it was never, not ever, held in place against any sort of wind by a bit of bent metal stuck in the sand ! What about an aircraft carrier or the QE 2 ..... you think they would be held by just their anchors lying on the sea bed anchor ? (Even if that anchor is the size of a middle sized house !).

If it's windy enough to lift the chain you need to let out more chain so that the weight of that lift increases until it is simply too much for the force of nature willing the boat in the other direction...... something to do with physics I believe !
The best way to explain it is imagine putting a small anchor and a load of chain in a bucket....... it is relatively easy to lift and move the bucket with the anchor and chain in it. Now lay out the anchor and all the chain and see if you can move it...... you can't, and it's not because the anchor is stuck in the sand !
 
Hi Mike.

Who did the survey?

If the Danforth is a reasonable size, I would say FlowerPower is on the money. 10mtrs chain and 40mtrs rope will be fine.

ETA - I would reckon on the Danforth needing to be more than a 5kg one, a 7.5kg just fine, a 10kg a bit hefty.
 
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Boatbore said:
Sorry but I can't agree with that.... ... my boat weighed 30 tons..... it was never, not ever, held in place against any sort of wind by a bit of bent metal stuck in the sand ! What about an aircraft carrier or the QE 2 ..... you think they would be held by just their anchors lying on the sea bed anchor ? (Even if that anchor is the size of a middle sized house !).

If it's windy enough to lift the chain you need to let out more chain so that the weight of that lift increases until it is simply too much for the force of nature willing the boat in the other direction...... something to do with physics I believe !
The best way to explain it is imagine putting a small anchor and a load of chain in a bucket....... it is relatively easy to lift and move the bucket with the anchor and chain in it. Now lay out the anchor and all the chain and see if you can move it...... you can't, and it's not because the anchor is stuck in the sand !
Click to expand...

You would wonder why we bother with an anchor then? And why all the serious discussion about anchor types?

I've been on container ships where the chain is taught and none is on the bottom, and they don't drag, and I have been on yachts where the chain is taught such that none is on the bottom and they don't drag. I've dived on anchors in similar circumstances and they don't drag. (I'm not saying that anchors never drag, obviously).

Letting out more chain creates a more horizontal pull on the anchor, discouraging it from being pulled out of the bottom but, once the pull exceeds a certain amount, the chain is at an angle to the bottom as it leaves the anchor.
 
A 20 lb Danforth some chain and 120 ft of rope will do fine as a lunch hook.

However if you anchor overnight in all weathers then think BIG. 30 lb Rocna and 200 ft of chain.

Remember when it is 4 am black as pitch and a 40 knot rain squall rattles through NOBODY says " Wish I had a smaller anchor and a bit less chain ".
 
Richard 10002.

You are correct that the anchor is relevant, and I shouldn't have implied it wasn't. But it is a small piece of the process only. If you will allow me to bang on, and I don't mean to argue (but cant help myself !) ..... when the chain is taut at the bow, it doesn't mean that all of it is lifted clear of the bottom. If a boat could be held in place on the hook alone, then the standard rule of 4x depth wouldn't apply. Imagine, hypothetically, a 100 mile piece of level sandy seabed 20 ft deep. Under normal circumstances you would lay the anchor plus about 55 ft of chain on the seabed and then another 25ft or so up to bow of your boat. If you used an invisible hand to pull the boat backwards then of course at some point all the chain would lift from the bottom and the only bit of resistance would, in theory be the hook. In practice though the downward force (gravity) of that taut chain is applying force to the bow of your boat, and in the direction directly opposite to that from the wind (or in my example the invisible force)....... so equal to the weight of 80 ft of chain in my example. If you laid 100 miles of chain in the same example, how much force would then have to be exerted on the boat to lift the 100 miles of chain......the answer is a lot more. So my point is that as the wind rises and the force propelling your boat onto the beach or wherever increases....more chain is what counteracts that force. Of course a bigger anchor helps but an extra 50ft of chain will add more benefit than a couple of extra sizes of anchor.......every time.

Would anyone else care to add to this ?
 
In my experience, a heavier anchor can help, sometimes.

The times things have gone wrong for me have been a mixture of causes:
- Once, too much current, not enough chain, anchor was simply dragged upwards and off the bottom. A heavier anchor would probably not have helped. More chain would have.
- Another time, hard sandy bottom, it failed to set. Possibly a different anchor design and something bigger would have helped.
- Dragged through the mud - F6-F7 in Newtown Creek in soft mud. The anchor had set, and there was 20m of chain out in 2m of water. But "backwards" I did go, ploughing a new furrow.
 
How about:

When the wind is high enough to lift all of the chain off the bottom, and you already have 7 or 10 times the depth out, it is the fact that the chain has a close to horizontal pull on the anchor which keeps it dug in, and holding the boat without dragging.

In similar circumstances, but with say 4 times depth out, the angle will be larger, the vertical pull greater, and more likelihood of the anchor being pulled upwards, losing its grip, and dragging.
 
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