Anchor chain/rope length for tidal Thames

[Grassman]

We're going on the tidal Thames from Limehouse to Barking Creek and then back up river to Lechlade in a few months time. As part of my research I have seen somewhere that I should have for my anchor configuration of 15m of chain and 35m of rope, so totalling 60m. Unfortunately I cannot find where I got it from because I'd cut and pasted it from wherever it was. I know it's a hell of a deep river but does it really have to be that long?

There's the cost of upgrading my current one but also it's going to take up a lot of room on the boat which I'd be happy to put up with for this trip, but as I wouldn't need it again I'd want to put my 18m shorter one back on afterwards.

I'd value your opinions please as to whether this depth is really necessary or would a little shorter than that be sufficient?. It just seems a lot for just a couple of days but I suppose it comes down to whether I want to risk not bothering to increase it from its current 18m.

What length have you other Thames users got?

[Alan de Enfield]

If you have 100% chain recommendation is 3 to 5 x water depth

If 50% Chain 50% Rope then 7x water depth

If short length of chain then 90% rope 10x water depth.

 

If water depth is (say) 30 feet then :

150 feet of chain, or

100 feet of chain and 100 feet of rope

[Dr Bob]

Alan's advice is spot on.

Your risk is certainly lower because you will only be on the river for a small number of days but the impact of something going wrong is still the same ie if you loose your engine,  you could loose your boat. If the river is low and slow then it might not be too bad but if not.......  You can reduce the length by attaching a 'chum' (ie a heavy weight - say 10Kg) about 5 metres from your anchor which means the chain from the anchor to the chum is tending towards being horizontal so the pull on the anchor is at the best angle but is that a good idea? You say you have 18m. Is that all chain? If so just get a sufficient piece of rope to splice on. I would go for 50m of rope to be on the safe side. Remember you only need the anchor if the engine fails and you have lost control. If that happens, by the time you have sussed out what is happening, and got someone up the front - who knows what they are doing, the current may have turned the boat and you are moving downstream. Setting an anchor when moving is not  a good idea and may not be successful. This is where having a length of rope is useful as you can pay it out slowly at the speed the boat is moving ie the anchor is then hardly moving in relation the bottom. You can then reduce the speed you pay it out so it digs in gently. If you just throw 20m of anchor and chain overboard in a 10m deep river and are moving at 4knts, you aint got a hope. Of course the anchor design will have a big say if it will set properly. Having a long piece of rope makes it easier to set.

Anchoring is a skill that you need to learn if you are in a boat that anchors frequently. NBs never need anchoring except in emergencies so people dont practice. It is not just a question of tossing the anchor and chain overboard which is why skimping on anchor and chain/rope is not a good idea.

 

[ditchcrawler]

But does anyone know how deep the river is so the OP can work out how long it needs to be. I don't have a clue what the depth would be but I guess someone from St Pancras boat club would know

[philjw]

Is there a resource that will tell us the expected depth of the river we are travelling on? Is this one of the dimensions published in the guides? 

Ditchcrawler beat me to it

Edited March 14, 2018 by philjw
cross post

[TheBiscuits]

https://webapp.navionics.com/#boating@11&key=cwgyHxU

 

Which shows just under 10 metres - or about 30 feet as Alan said above.

Edited March 14, 2018 by TheBiscuits

[howardang]

It is always surprising to see that people want know the minimum amount of cable/rope they can get away with. Far better to carry the most you can carry. I would rather have some left in the locker that I could deploy, rather than wish I had more! There seems to be a general misconception that there is only one length to use for each anchoring situation rather than the reality where you deploy sufficient for the specific circumstances, but you have more just in case......

 

Howard

Edited March 14, 2018 by howardang

[TheBiscuits]

Just now, howardang said:

It is always surprising to see that people want know the minimum amount of cable/rope they can get away with. Far better to carry the most you can carry. I would rather have some left in the locker that I could deploy, rather than wish I had more! There seems to be a general misconception that there is only one length to use for each anchoring situation rather than the reality where you deploy sufficient for the specific circumstances. 

That makes sense if you have a dedicated chain locker, but could be a recipe for disaster if you don't.

I always think hope these type of questions are more about "Is what I have enough" rather than "What's the least I can get away with"

[ditchcrawler]

21 minutes ago, howardang said:

It is always surprising to see that people want know the minimum amount of cable/rope they can get away with. Far better to carry the most you can carry. I would rather have some left in the locker that I could deploy, rather than wish I had more! There seems to be a general misconception that there is only one length to use for each anchoring situation rather than the reality where you deploy sufficient for the specific circumstances, but you have more just in case......

 

Howard

But where do you stop, 100 mts, 200 mts 500 mts?

[Dr Bob]

3 minutes ago, ditchcrawler said:

But where do you stop, 100 mts, 200 mts 500 mts?

100m should be ok for most cases.

[TheBiscuits]

2 minutes ago, Dr Bob said:

100m should be ok for most cases.

Except that one where you need to deploy 50M from the weir ... and panic!

[howardang]

20 minutes ago, ditchcrawler said:

But where do you stop, 100 mts, 200 mts 500 mts?

No, you use your common sense, and carry enough (with a reserve) to allow for the maximum depth that you may have to anchor in. Only you know what that max depth would be.

Howard

 

[David Mack]

19 minutes ago, TheBiscuits said:

Except that one where you need to deploy 50M from the weir ... and panic!

Except that there aren't any weirs on the tidal Thames where you might need 100m of rope.

[Scholar Gypsy]

Hi - I assume you are coming on the SPCC trip in May, in which case I look forward to meeting you then. I normally come along (with my radio and depthsounder...)  as crew on someone else's boat. I'd say four things:

1.  The deepest  bit is about 9m (plus the height of the tide)
2. The 15+35m guidance is from the PLA & Coastguard, actually originally formulated for the Diamond Jubilee pageant and so maybe a bit OTT. That's what I have got. I stop the long line from getting in a mess by using whipping twine to hold it in place.
3. Their current guidance for cruisers (I think that means yogurt pots not NBs, but never mind) on this and much else is here: https://boatingonthethames.co.uk/Cruising , where it says 5+25. 
4. Unless something has gone seriously awry, you'll be travelling in groups of at least three, and if you keep close to each other then you are able to get assistance from another boat. This is covered in detail at the safety briefing. The basic point here is that it's better to get a tow than drop the anchor, but you must have an anchor in case that mode of rescue is not available (eg if the other two boats are already rescuing each other, or they have not been keeping a proper lookout behind). 

We do the trip at gentle canal cruising speed - there's plently of time to kill before we get to Brentford/Richmond - and so the risk of overheating etc is very low. The main hazard is fuel problems, ie people with water/crap/bug at the bottom of their tank being stirred up. This has happened twice to me now, on boats I have been crew on, and it's quite exciting. Fortunately we had 2-3 minutes warning that something was awry before the engine cut out, so we could summon help before the engine failed. So please do take a sample from the bottom of the tank, and consult a fuel polisher if it is not clean.

Oh and it worth remembering that if you have a problem within say 3-400 feet of a bridge then by the time you have decided to drop the anchor, got to the other end of the boat, turned the boat round etc, you will have arrived at the bridge. With luck/skill you will be on the right line so you go through the bridge not hit the pier.

Just a few photos from 2017 here:  https://nbsg.wordpress.com/2017/05/15/spcc-tideway-trip-2017/

[MHS]

The length of chain required will also surely depend on the weight of the anchor and also that of the chain. I’ve seen some very small anchors with thin anchor chain on narrowboats. Can’t imagine they would help, except giving them a false sense of security. 

[LadyG]

On 14/03/2018 at 17:00, Grassman said:

We're going on the tidal Thames from Limehouse to Barking Creek and then back up river to Lechlade in a few months time. As part of my research I have seen somewhere that I should have for my anchor configuration of 15m of chain and 35m of rope, so totalling 60m 50meters 

Corrected that for you.

Edited March 16, 2018 by LadyG

[Grassman]

Thanks to you all for your very helpful suggestions. I'm sorting out the preparation including fuel polishing, new filters etc. Regarding the anchor, chain, and rope - My anchor is one of those that collapses flat which many narrowboats have (I'm note sure of the technical name), and the previous owners did a lot of tidal rivers with it, not that that means it's the correct one of course, and I don't think they ever needed to use it. But it's quite big.

I think I might have solved the issue because I've found somebody on our marina who has a chain which could if I wanted make my total length about 50m (rope 12m & chain 38m) which judging by what some of you have said, should be sufficient???   

[Naughty Cal]

On 3/14/2018 at 19:22, David Mack said:

Except that there aren't any weirs on the tidal Thames where you might need 100m of rope.

Plenty of bridges to hit instead though.

[Grassman]

I forgot to mention - If any of you others fancy accompanying us with your boat, we plan to leave Limehouse early doors (5am - 7am) during a 3 day window of Saturday July 7th-9th and heading up river. The tides will be conducive and there will be little river traffic at that time in the morning. 

I asked this question in January but had no takers, but now it's a bit nearer the time I thought I'd ask again. There would be the mutual benefit of having another boat nearby in case if difficulties as well as some good photo opportunities.

[LadyG]

12 minutes ago, Grassman said:

Thanks to you all for your very helpful suggestions. I'm sorting out the preparation including fuel polishing, new filters etc. Regarding the anchor, chain, and rope - My anchor is one of those that collapses flat which many narrowboats have (I'm note sure of the technical name), and the previous owners did a lot of tidal rivers with it, not that that means it's the correct one of course, and I don't think they ever needed to use it. But it's quite big.

 

That'll be your Danforth.

Edited March 16, 2018 by LadyG

[phantom_iv]

Bear in mind that chain is (intentionally!) very heavy, so unless you have a powered anchor windlass you'll be needing to be able to lift the combined weight of anchor + chain to recover it following deployment - or at least be able to lift it over the side if you're considering it an emergency consumable. However bear in mind in may not set and hold fast on the first attempt, so you may need to recover it and have another go. You might think its unlikely that your anchor will fowl some unattached debris on the river bed that'll stop it setting properly - but that's exactly what happened to me the first time I deployed an anchor in a dangerous situation following an engine failure... not fun!

It should be fairly obvious from the design of the danforth anchor that it's designed to dig in and resist horizontal forces, not vertical ones - so having the intentionally heavy chain keeps the anchor aligned to the sea bed, then you need a long enough line  to make the angle the anchor is pulled at approximately horizontal - the more line you have the better this approximation is, but obiously there's a tradeoff with storage and handling (& indeed cost!)

So I'd say get as much chain as you think you can manage with your anchor, then attach plenty of rope.

[Alan de Enfield]

35 minutes ago, phantom_iv said:

Bear in mind that chain is (intentionally!) very heavy, so unless you have a powered anchor windlass you'll be needing to be able to lift the combined weight of anchor + chain to recover it following deployment - or at least be able to lift it over the side if you're considering it an emergency consumable

But you are only lifting 'the depth of water' of chain at any one time and 10mm chain is about 2kg per metre.

Once you can recover the anchor, motor back up over it hand balling the chain in as you go, when you are over the anchor, a little blast of power will flip the anchor over and you can pull it in.

If, for any reason you cannot recover it, either buoy it off and get the local scuba club to recover it for you or, 'right-off' the cost (a small cost for potentially saving the loss of a £1000's boat and possibly your life).

 

If you really cannot handle it and want to recover it, then there is a simple method that does not require much in the way of lifting - widely used on 'small seagoing fishing boats'.

Its a method called 'using an Alderney ring' and the boat does all of the work.

 

Edited March 16, 2018 by Alan de Enfield

[phantom_iv]

Good point - I'm still not sure I'd want want to pull up too many 10s of metres of 10mm chain though with a decent anchor attached.

I'd love to see that technique demonstrated by a narrowboat on the tidal thames though with say a 25kg anchor and 30m of chain ;-)

[Scholar Gypsy]

I do have an anchor buoy connected to the bottom end of the anchor, which in theory would assist retreival....

[ditchcrawler]

4 hours ago, phantom_iv said:

Bear in mind that chain is (intentionally!) very heavy, so unless you have a powered anchor windlass you'll be needing to be able to lift the combined weight of anchor + chain to recover it following deployment - or at least be able to lift it over the side if you're considering it an emergency consumable. However bear in mind in may not set and hold fast on the first attempt, so you may need to recover it and have another go.  

Do you get a second chance in a Narrowboat, you are not mooring up to go for a swim, you are doing it because you cant drive the boat anywhere. How did you manage to retrieve and reset? I think yours is the only posting I have seen from someone who has had to use one.