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Anchor Stuff


frygood

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Hi Guys

Sorry about this.I have an Anchor [25kg] which i brought in a well known Chandlers along with a rope and chain which the Chandlers also supplied with it.Today i had it all out and measured the rope about 7m and the chain is also about 7m.Now i feel these are properly to short for say a trip on the Thames or some of the larger rivers.

My Question is.Do i add more Chain or more rope or both and how much.

 

Thanks  Carl

 

 

 

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As much chain as you can afford and stow.

 Most of the holding power of an anchor is in the cable that, if set properly,lies along the bottom

  The anchor itself mainly keeps the cable straight as it lays out.

Ideally  you then want enough rope that all the chain cable, and a bit of the warp,  is able to lie on the bottom. That means 1 1/2 to 2 times as much rope as the deepest water you want the anchor to hold in.

 

Using an anchor as an emergency brake is a lot more demanding than doing it deliberately, and you need good gear for it to work.  Especially, Do check that you have a substantial fastening for the inboard end of you anchor cable.

 

N

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45 minutes ago, frygood said:

Hi Guys

Sorry about this.I have an Anchor [25kg] which i brought in a well known Chandlers along with a rope and chain which the Chandlers also supplied with it.Today i had it all out and measured the rope about 7m and the chain is also about 7m.Now i feel these are properly to short for say a trip on the Thames or some of the larger rivers.

My Question is.Do i add more Chain or more rope or both and how much.

 

Thanks  Carl

 

 

 

Port of London authority suggests a minimum of 5m chain and 25m rope for use on their river.  Hope that helps answer your question.

 

https://www.pla.co.uk/assets/sb3of2014-dangerofinadequatesimplemaintenancechecks.pdf

Edited by Chewbacka
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1 hour ago, frygood said:

Now i feel these are properly to short for say a trip on the Thames or some of the larger rivers.

 

You need to tell s which rivers.

 

The non-tidal Thames is a total pussycat and anchors are superfluous. Same for the River Wey.

 

Tidal Thames and Trent etc totally different kettle of fish. Which rivers are you planning on cruising, exactly?

 

 

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9 hours ago, frygood said:

Today i had it all out and measured the rope about 7m and the chain is also about 7m.

That will be sufficient for Rivers up to about 2.5 - 3 metres deep.

Insufficient for anything deeper.

The 'rule of thumb' is 

 

100% chain = (minimum) 3x expected depth, ideally 4x depth

100% Rope = 10x depth

50/50 = 7x depth 

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3 minutes ago, Rickent said:

What is the recommended thickness of rope for use with an anchor on a narrowboat?

How thick is a piece of string ?

 

Too many variables to make an open-ended recommendation.

 

My suggestion would be 100% 'half inch' (12mm) chain.

Edited by Alan de Enfield
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6 minutes ago, Alan de Enfield said:

How thick is a piece of string ?

 

Too many variables to make an open-ended recommendation.

 

My suggestion would be 100% 'half inch' (12mm) chain.

There must be some minimum thickness recommended for the rope attached to the chain as it would be under a great deal of strain when deployed in an emergency situation on a fast flowing river.

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1 minute ago, Rickent said:

There must be some minimum thickness recommended for the rope attached to the chain as it would be under a great deal of strain when deployed in an emergency situation on a fast flowing river.

The strength needed will depend on the weight of the boat (have you got a 2 tonne aluminium 'waterbaby', or a 20 tonne full length NB) the speed you are travelling (water flow) will also affect the loading.

 

I would be loathe to make a recommendation for something I am unsure about - it only takes me to say "use 19mm" and if it breaks and you have a disaster and sue me  ……………...

 

I would only suggest the use of 100% chain. You need less of it, it will store in a smaller space (bucket) and it will do the job.

BUT - costs more than a piece of string.

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I am thinking of starting a CWDF unanswerable questions thread.

  • How little can I get away with continuous not cruising?
  • How big/type of anchor? How much/thickness chain? Length/diameter/type of rope for said anchor?
  • Which is better, pump out, or cassette?

 

As has been said before, the experience base for deploying an anchor from a narrowboat in anger is tiny. The combination of possible river depths, flow speed, river bed type, anchors, chains, warps and so on is so huge and no experiments have been done that I am aware of. Basically, nobody knows. All opinions are based on gut feel, or carried over from lumpy water sailing, where anchors are commonly used, but under different circumstances and with different sorts of boats.

 

In Summary:

  • The heaviest anchor you can still lift.
  • The longest heaviest chain you can afford and have space for.
  • The longest thickest bit of rope you can afford and have space for.
  • Attach the rope to something really strong. A T stud may break off with the shock load. I tie mine through a well deck scupper and around the hull sides as a back up to the T stud.

These give you the highest probability of being able to hold the boat in an emergency. Failed engine in a fast flowing river, heading towards a weir.

 

My personal opinion, based on caving and climbing experience is to use a stretchy rope in the system, rather than a non-stretch rope, or all chain system. This reduces the peak force on the whole anchor/chain/rope/attachment entity as it halts the boat and reduces the risk of the anchor ripping out, or something breaking.

 

Jen

 

Edited by Jen-in-Wellies
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41 minutes ago, Alan de Enfield said:

The strength needed will depend on the weight of the boat (have you got a 2 tonne aluminium 'waterbaby', or a 20 tonne full length NB) the speed you are travelling (water flow) will also affect the loading.

 

I would be loathe to make a recommendation for something I am unsure about - it only takes me to say "use 19mm" and if it breaks and you have a disaster and sue me  ……………...

 

I would only suggest the use of 100% chain. You need less of it, it will store in a smaller space (bucket) and it will do the job.

BUT - costs more than a piece of string.

Not looking to sue you Alan, but I take your point there are too many variables, just wasn't sure if there was a minimum recommended thickness. 100% chain would be the best solution if possible and practical. 

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10 minutes ago, Rickent said:

100% chain would be the best solution if possible and practical. 

What would be the reasons why it wouldn't be ?

 

My boats (Steel NBs & GRP Cruises) have always had 100% chain.

You can get sufficient chain in a bucket so it makes storage easy and tidy.

 

The Trent is rarely above 15-20 feet deep so (as an example) you would only need 20 metres of chain.

 

10mm chain is in all likelihood the size to use (I quoted 12mm above to be 'over the top')

 

There is 30 metres on ebay as a buy-it-now for £110 (but unless local you would need a carrier to pick it up for you)

 

https://www.ebay.co.uk/itm/10mm-Galvanised-Chain-x-30-Metres-Boat-Anchor-Calibrated-Chain-buyer-collects-/323843650189?_trksid=p2385738.m4383.l4275.c10

 

Or, buy it new at about £7 per metre

 

https://www.gsproducts.co.uk/10mm-galvanised-steel-short-link-chain/

Edited by Alan de Enfield
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10 minutes ago, Alan de Enfield said:

What would be the reasons why it wouldn't be ?

Because in most cases we would want to stop a moving boat with the anchor, rather than hold a stopped boat against a current. It is a dynamic system. A 20 ton boat, even moving at only a few miles an hour has a considerable amount of energy that will need to be absorbed as anyone knows who has tried to stop a moving boat with a centre line. The peak force on the anchor/chain/rope/attachment point system will depend on how much stretch there is. A chain only system will have a very high peak force. A chain, plus a length of rope, a much lower peak force.

Imagine trying to stop a slowly moving boat with a chain tied round a bollard and trying to stop a rope with a rope tied round a bollard. Less likelyhood of broken crockery on board if a rope is used. In practice we allow the rope to slip and absorb the energy with friction against the bollard, so not a total analogy, but close enough.

Jen

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1 hour ago, Jen-in-Wellies said:
  • How little can I get away with continuous not cruising?
  • How big/type of anchor? How much/thickness chain? Length/diameter/type of rope for said anchor?
  • Which is better, pump out, or cassette?
  • How long will my new batteries last?
  • Why is there water in my bilge?
  • Haha 1
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1 hour ago, Jen-in-Wellies said:

A T stud may break off with the shock load.

 

What shock load is that then?

 

Even if the anchor sets 100% solid (v unlikely), the chain and wrap will initially be in a catenary shape which when tightened, becomes ever nearer to straight, but the point is this causes the load on the tee stud or whatever gets applied and increased progressively over a short interval rather than being applied  instantaneously. So no shock load.

 

in addition as you say, any warp will have a degree of elasticity which will increase the  damping of any shock effect.

 

Agree with you about this all being armchair speculation though! 

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3 minutes ago, Mike the Boilerman said:

 

What shock load is that then?

 

Even if the anchor sets 100% solid (v unlikely), the chain and wrap will initially be in a catenary shape which when tightened, becomes ever nearer to straight, but the point is this causes the load on the tee stud or whatever gets applied and increased progressively over a short interval rather than being applied  instantaneously. So no shock load.

 

in addition as you say, any warp will have a degree of elasticity which will increase the  damping of any shock effect.

 

Agree with you about this all being armchair speculation though! 

Yes, the tightening of the chain and warp against gravity and water resistance to a near straight line will help reduce the peak load a lot. Good point. Still think a more stretchy warp is a good idea, rather than all chain.

Written from a sofa, so not armchair speculation. ?

Jen

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11 hours ago, Mike the Boilerman said:

 

You need to tell s which rivers.

 

The non-tidal Thames is a total pussycat and anchors are superfluous. 

 

I'd have to disagree. It depends on how the river is running and which reach you're on. Even with no stream warnings some narrower reaches can flow quite fast. So an anchor isn't superfluous on the non-tidal Thames if your engine happens to stop upstream of a bridge or a weir, it's a prerequisite.

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On the weight point, I  had some fun deploying my anchor, in  a controlled way,  in the Wash a couple of weeks ago.  15m chain of varying thickness. 

 

Recovery was quite tricky,  I think a combination of two factors

 

1) the weight of the chain,  which is actually quite a bit more than my 20kg anchor.  

2) the pitching movement of the boat,  in an light swell. It was impossible to hold onto the boat and pull the anchor up.

 

Next time I would attach a lighter line and buoy to the bottom of the anchor,  and use that too assist recovery. DSC_4588.JPG.54049ce21f21b179a39f19f44132dde8.JPG

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The float system seems to work by going fast enough such that the drag of the float causes the rope and chain to pull through the ring, overcoming the weight of the small anchor.  No way my narrow boat could go fast enough to pull 10mm chain holding a 14kg anchor.  Nice idea though. 

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16 minutes ago, Chewbacka said:

The float system seems to work by going fast enough such that the drag of the float causes the rope and chain to pull through the ring, overcoming the weight of the small anchor.  No way my narrow boat could go fast enough to pull 10mm chain holding a 14kg anchor.  Nice idea though. 

He mentioned 5mph in the video.

Certainly I never needed to go above 'walking speed' when I used it on our fishing boat. (10mm chain and 20kg anchor)

 

I never used it on a NB but I would be fairly confident it would work.

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22 hours ago, Mike the Boilerman said:

 

You need to tell s which rivers.

 

The non-tidal Thames is a total pussycat and anchors are superfluous. Same for the River Wey.

 

Tidal Thames and Trent etc totally different kettle of fish. Which rivers are you planning on cruising, exactly?

 

 

I am currently on the Avon and will be heading up the Seven.With maybe a trip down to Glocester but I'm not sure about that.As for the rest I have nothing planed as yet.I just want to get it right for when i do.

Edited by frygood
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