How long should your anchor chain be?

[Scholar Gypsy]

A cautionary tale from an incident earlier this year on the Humber ...

 

https://assets.publishing.service.gov.uk/media/5bd8374540f0b6051e77b6c0/2018_-_18_-_Celtic_Spirit.pdf

[Ray T]

When a youngster I was in The Boys Brigade and this was their theme Hymn:

 

Will your anchor hold in the storms of life, When the clouds unfold their wings of strife? When the strong tides lift, and the cables strain, Will your anchor drift or firm remain?   When ever I sailed offshore the words always came to mind

[Naughty Cal]

Just goes to show that even the professionals don't get it right all of the time.

 

 

[Alan de Enfield]

10 minutes ago, Naughty Cal said:

Just goes to show that even the professionals don't get it right all of the time.

 

 

Or - don't develop complacency, or, it'll never happen to me attitude.

The Sea is a cruel mistress but at least there is room to 'cock-up', on the tidal rivers you have much higher (but slightly different) risks - I think I am always more 'aware' (maybe apprehensive) on the rivers than I am at Sea.

[rowland al]

Ours is ‘quite long’ but it’s an interesting question. On canals there is unlikely to be a need for an anchor. On river and sea crossings you need to know the maximum depth (and adjust for highest tide).

 

Not many ‘canal’ boaters will ever do a sea crossing (unlike you) but I guess you’d need a chart for the particular crossing to decide on the correct length of your anchor chain. 

 

I’ve been on a few inland rivers including the Soar, Thames and Trent (tidal and non-tidal). There were a few occasions I wished I had the anchor at hand especially when I was caught in floods. I now always have it on hand for rivers. Getting something jamming my  prop was all I needed to learn that lesson. 

 

So my question is, is there any information out there providing the maximum depth of inland rivers (bearing in mind that an allowance for tide and flood is also needed in the calculation)? 

 

 

[Tanglewood]

I think the answer gives rise to the idiom, 'how long is a piece of string?'   It's the length of whatever ties it to your boat that is important, and the knot you use to do so, as can be attested by all those unfortunates whose knot slipped whilst at anchor.  

[rowland al]

1 minute ago, Tanglewood said:

I think the answer gives rise to the idiom, 'how long is a piece of string?'   It's the length of whatever ties it to your boat that is important, and the knot you use to do so, as can be attested by all those unfortunates whose knot slipped whilst at anchor.  

If you know the maximum depth you are going to encounter (given tidal and flood conditions) you can calculate a sensible anchor chain length.

 

The problem is not knowing the maximum depth, and it’s solvable providing you have that information . 

[ditchcrawler]

I have cruised the Thames, Severn, Avon, Trent, Great Ouse and don't have a clue how deep they are, I don't expect many people do. I also don't have 5 shackles of cable on my anchor

[Detling]

generally if you have insufficient cable/line the water is deep enough to keep you afloat. Even with an adequate scope you should keep an eye on things, check you are actually anchored and not dragging, using transits on shore eyeball required, gps will show but if you are dragging it may only be 20 feet a minute so gps won't pick it up for ages. Just because you were stationary doesn't mean you will stay stationary, tides rise and turn causing you twist the anchor round thus needing to re-dig it in, winds also strengthen and swing the boat wriggling the anchor. Normal practice is to have an anchor watch who checks at least every 10 minutes and logs it.

[artleknock]

6 minutes ago, Detling said:

 Normal practice is to have an anchor watch who checks at least every 10 minutes and logs it.

I'll train her indoors to do that next time I am on the Nene.

[rowland al]

29 minutes ago, ditchcrawler said:

I have cruised the Thames, Severn, Avon, Trent, Great Ouse and don't have a clue how deep they are, I don't expect many people do. I also don't have 5 shackles of cable on my anchor

Well Google says the Thames is about 20m deep in the estuary. Conversely, when we went through Henley we shared a lock with someone who was punting. 

 

Thats about all I know! 

[Naughty Cal]

38 minutes ago, ditchcrawler said:

I have cruised the Thames, Severn, Avon, Trent, Great Ouse and don't have a clue how deep they are, I don't expect many people do. I also don't have 5 shackles of cable on my anchor

The depth on the tidalTrent last week varied from about 5ft to 35ft depending on where we were on the river.

[Tony Brooks]

6 minutes ago, rowland al said:

Well Google says the Thames is about 20m deep in the estuary. Conversely, when we went through Henley we shared a lock with someone who was punting. 

 

Thats about all I know! 

That is about all you can know. The Thames Conservancy used to publish the minimum navigation depth but I can't find that. Here is another source that looks about right. https://www.waterways.org.uk/waterways/canals_rivers/river_thames_non-tidal/gauge_information

 

For anchoring I would always assume double the depth but then I would gradually let the full length of rode out in an emergency and not faff about worrying it its 2 or 4 metres deep at that point.

 

It ranges from 5ft 6" above Teddington to 3ft above Kings lock but this is a river so any depth is the minimum and you could well find it much deep on the outside of bends or in narrows and weir streams. However any deep parts are likely to be comparative short sections a dragging anchor would soon reach a shallower part. No good if its dragging because it does not match the bottom or it weight and rode are too light.

[rowland al]

13 minutes ago, Tony Brooks said:

That is about all you can know. The Thames Conservancy used to publish the minimum navigation depth but I can't find that. Here is another source that looks about right. https://www.waterways.org.uk/waterways/canals_rivers/river_thames_non-tidal/gauge_information

 

For anchoring I would always assume double the depth but then I would gradually let the full length of rode out in an emergency and not faff about worrying it its 2 or 4 metres deep at that point.

 

It ranges from 5ft 6" above Teddington to 3ft above Kings lock but this is a river so any depth is the minimum and you could well find it much deep on the outside of bends or in narrows and weir streams. However any deep parts are likely to be comparative short sections a dragging anchor would soon reach a shallower part. No good if its dragging because it does not match the bottom or it weight and rode are too light.

Thanks Tony, but there is a bit of a difference between max draft allowed/recommended and actual depth though. We’re looking for the maximum depth, not minimum for anchoring. 

 

I’m guessing most of us with an anchor on a narrow boat, we just use what was supplied with the boat or, like me, ask someone else and hope it’s long enough. ?

[Alan de Enfield]

20 minutes ago, Naughty Cal said:

The depth on the tidalTrent last week varied from about 5ft to 35ft depending on where we were on the river. & the height of the tide.

A couple of weeks ago the non-tidal section of the Trent (From County Hall Steps to Cromwell Lock probably averaged about 15-20 feet.

 

Mostly 10-12 feet some reasonable runs of 'high 20's' but we bottomed out in a couple of places at about 4 feet (around Burton Joyce area).

 

I'd suggest having a minimum of 60 feet of chain on the Trent (assuming you are 100% chain) - you can always add a length of rope to the end if it proves to be insufficient.

 

 

[Tony Brooks]

8 minutes ago, rowland al said:

Thanks Tony, but there is a bit of a difference between max draft allowed/recommended and actual depth though. We’re looking for the maximum depth, not minimum for anchoring. 

 

I’m guessing most of us with an anchor on a narrow boat, we just use what was supplied with the boat or, like me, ask someone else and hope it’s long enough. ?

That's the whole problem on a river, I doubt anyone knows the maximum depth unless they sounded it AND the depth is likely to alter with scouring and silting. This is why I am not going to get to hung up on anchoring lengths as long as I feel I have enough.

[rowland al]

8 minutes ago, Alan de Enfield said:

A couple of weeks ago the non-tidal section of the Trent (From County Hall Steps to Cromwell Lock probably averaged about 15-20 feet.

 

Mostly 10-12 feet some reasonable runs of 'high 20's' but we bottomed out in a couple of places at about 4 feet (around Burton Joyce area).

 

I'd suggest having a minimum of 60 feet of chain on the Trent (assuming you are 100% chain) - you can always add a length of rope to the end if it proves to be insufficient.

 

 

That’s what we have (with a long length of rope). Phew! 

 

I am right in saying it’s better to have an anchor deployed at the bow on a narrow boat? Also, if you do get stranded on a mud flat, how can you avoid getting sucked in? 

2 minutes ago, Tony Brooks said:

That's the whole problem on a river, I doubt anyone knows the maximum depth unless they sounded it AND the depth is likely to alter with scouring and silting. This is why I am not going to get to hung up on anchoring lengths as long as I feel I have enough.

Yes, but what is ‘enough’? Lol.

 

20 metres of chain and rope sounds ‘enogh’ - I hope. 

[Alan de Enfield]

8 minutes ago, rowland al said:

I am right in saying it’s better to have an anchor deployed at the bow on a narrow boat?

 

Yes (really applies to any boat)

 

8 minutes ago, rowland al said:

Also, if you do get stranded on a mud flat, how can you avoid getting sucked in? 

1) Just hope that you have enough buoyancy when the tides comes in so it lifts you off.

2) You can assist by 'digging around the boat' and breaking the seal if in doubt.

3) Run a rope under the bow of the boat (from side to side), using a 'sawing' action work the rope to the back end - not easy if you are singlehanded

4) Call for help (Channel 74 VHF) and await a tow.

5) Flag down a passing boat and request a tow. (offer them your 'tow-rope', if you accept theirs then they are able to claim salvage charges)

Edited November 1, 2018 by Alan de Enfield

[ditchcrawler]

1 hour ago, Naughty Cal said:

The depth on the tidalTrent last week varied from about 5ft to 35ft depending on where we were on the river.

I worry more at the 5 foot bit rather than the 35 and when it gets to 3ft, well.

[Scholar Gypsy]

For tidal rivers I have 15m chain and 35m of rope. The latter is neatly tied up with whipping twine to stop it getting tangled on the boat.

The max reading I got when crossing the Wash was 22m or so, but if engine failed I would drift a bit closer to land before dropping the anchor (and also call for help straightaway!).  I did find an 8m hole on the outside of the hairpin bend just above Gainsborough.

[Iain_S]

Interesting that the recommendation in the MAIB report is 6 to 10 times water depth. Bearing in mind that that is all chain, the 3 to 5 times depth usually stated seems on the optimistic side!

[Alan de Enfield]

5 minutes ago, Iain_S said:

Interesting that the recommendation in the MAIB report is 6 to 10 times water depth. Bearing in mind that that is all chain, the 3 to 5 times depth usually stated seems on the optimistic side!

Conditions and bottom certainly dictate the amount of chain needed.

We have moored up (anchored) about 500 yards away from these 'commercial' moorings - we had 6x depth of chain out and went to bed, anchor alarm went off and we were dragging, we eventually ended up with 10x depth out and were still dragging, so, anchor 'back up' motored back to our start position and deployed the anchor again with 10x depth out - we held this time but we still had some one on watch all night.

 

The bottom there is not particularly good holding, and as the tide changes and you start to swing around it is 'easy' to actually pull the anchor out backwards, so it does pay to 'be aware'.

We always have a kedge anchor ready to deploy, but that boat had lost its Port anchor so didn't have that option.

[rowland al]

13 minutes ago, Iain_S said:

Interesting that the recommendation in the MAIB report is 6 to 10 times water depth. Bearing in mind that that is all chain, the 3 to 5 times depth usually stated seems on the optimistic side!

I’m glad my narrow boat doesn’t weigh 2840 tonnes (even with me on it)

[Clodi]

7 hours ago, Alan de Enfield said:

  5 hours ago, rowland al said:

I am right in saying it’s better to have an anchor deployed at the bow on a narrow boat?

The only problem with this is when travelling downstream  where there is not enough room for a narrowboat to swing around, you definitely don't want to end up wedged across the stream.

Sometimes common sense must contradict  the 'rule'. Hopefully we'll never need to have to use ones anchor, however I grew up on the Great Ouse and conditions can change rapidly catching even experienced locals out.

I live in West-Wales and just a couple of weeks ago we suffered tremendous rainfall causing our local river systems to rise by 20' practically overnight, unfortunately claiming a young mans life and breaching flood defences causing millions of pounds worth of damage. Always prepare for the unexpected.

[David Mack]

12 hours ago, Naughty Cal said:

Just goes to show that even the professionals don't get it right all of the time.

 

 

Yes. For some of them, boating is a contact sport.