Displacement vs Chain MBL

[PhillM]

I am still deciding what anchoring rode to carry on Paean. She came with 20m of 8mm chain which was OK for most instances but heavy in the bow.

Last year I finally put on a 10m of 8mm chain and 40m warp but didn't get round to using it. The main worry I have singlehanded is if in a tidal stream, I need to motor towards the anchor on tick over while being on the bow hauling it up. I hate the idea of overrunning the warp and getting it around the prop. So I would like all chain.

I am looking at 40 or 50 m of Titan G40 6mm. Weight in the bow is acceptable. However, it has a MBL of 1800 KG. Paean is only 24 foot but displaces 3T. My question is, does the chain need to be able to hold the displacement of the craft. I would guess not, as its the force of the craft moving through the water that matters. Thoughts?

 

[doug748]

It's difficult to imagine your boat ever tugging more than 1000 lbs even snubbing (which you will avoid anyway) in very poor conditions. So I personally would be happy with what you propose.

Some people will say you can't be too careful etc etc and end up with safety margins of 8, or more, but you have to call a halt at some point. If you built aircraft like that they would never fly.
The weakest link is often the shackle so source one from the chain people and make sure it exceeds the strength of the chain.

.

 

[BabaYaga]

She came with 20m of 8mm chain which was OK for most instances but heavy in the bow.

Last year I finally put on a 10m of 8mm chain and 40m warp but didn't get round to using it. The main worry I have singlehanded is if in a tidal stream, I need to motor towards the anchor on tick over while being on the bow hauling it up. I hate the idea of overrunning the warp and getting it around the prop. So I would like all chain.

I am looking at 40 or 50 m of Titan G40 6mm. Weight in the bow is acceptable. However, it has a MBL of 1800 KG. Paean is only 24 foot but displaces 3T.

It seems to me that 20m of 8mm chain + 40m of warp (say 14mm octoplait) will give you about the same weight in the bow as 40m of 6mm chain. So the latter option means a shorter rode with a significantly lower strength (although it may well be enough).
With 20m of chain, rather than 10m, it seems that you should be able to get the rope in (perhaps by using the sheet winch) before you have to rely on the engine while hauling.

 

[Tranona]

6mm is fine. I had 40m of 6mm and 20m of 12mm 3 strand on my old 26' with a 25lb CQR and never had a problem. Only time I ever went into the rope was in the Channel Islands. Anchoring just about anywhere on the South coast in places where you would want to stay overnight is unlikely to require more than 40m. No doubt you will use a more modern anchor than the CQR, although the latter is perfect for the d bottoms of many places in the Solent or Poole.

 

[PhillM]

Thanks guys. The anchor IS an old CQR and it might be a copy but it’s never failed to set ok. I am thinking that I’ll get 50m and perhaps splice some warp next year before I head for the Channel Islands and Brittany.

Re winches, what are these things of which you speak? Paean is an old classic with a couple of Pepperpot tufnal thingys which act as turning blocks. When the sheet is too hard to hand pull, it’s time to put a reef in.

 

[V1701]

I'd be tempted to have 20 or 25m of 6mm chain and 30m or a bit more of octoplait. Then you already have your snubber. Have similar on a Bowman 26 but I did replace the old (not very good) CQR as well...

 

[doug748]

Thanks guys. The anchor IS an old CQR and it might be a copy but it’s never failed to set ok. I am thinking that I’ll get 50m and perhaps splice some warp next year before I head for the Channel Islands and Brittany.

50m should do you most of the time.
I might splice on more if I was resident around the bay of St Malo but probably not, I like to keep the extra stuff to shackle on if I need it, which is not a lot.
In the cockpit locker it stays clean, dry and ready for other uses.

.

 

[Channel Sailor]

With 20m of chain, rather than 10m, it seems that you should be able to get the rope in (perhaps by using the sheet winch) before you have to rely on the engine while hauling.

I suggest owners/operators should be aware of the designed maximum load on deck winches such as a Sheet winch. A Harken 35 two speed is 650kgs. A size 20 is 550kgs. Maybe treat it the same as you would an dedicated anchor winch, which would be to never load it with the windage/tide drag weight of the yacht, only the weight of the chain and a free anchor. For a small yacht 550kgs is quite a high load, but it could, when getting that stuck anchor out the mud, not doing your winch any good.

Also a Sheet winch load (for at least some make of winch) are intended to arrive on the winch from certain direction. So I suggest it worth checking the installation instructions if you are changing the direction of the winch load compared to how it was designed/installed.

I would guess it is not a problem for just winching the weight of the slack, or say 12m of vertical chain with a freed 15kg anchor on the end.

 

[dom]

Last year I finally put on a 10m of 8mm chain and 40m warp but didn't get round to using it. The main worry I have singlehanded is if in a tidal stream, I need to motor towards the anchor on tick over while being on the bow hauling it up. I hate the idea of overrunning the warp and getting it around the prop. So I would like all chain.

Phil, if fouling the prop is a big concern, have you considered a weighted anchor rode? Just a thought:

Leaded Anchor Warp - Jimmy Green Marine

 

[Pete7]

Phil, would it help if you chose a different 6mm chain with a MBL of 2447kgs?

6mm DIN766 Lofrans Grade 40 Calibrated Anchor Chain

I would change to 6mm but the windlass needs changing too which starts to add up.

Pete

 

[BabaYaga]

I suggest owners/operators should be aware of the designed maximum load on deck winches such as a Sheet winch. A Harken 35 two speed is 650kgs. A size 20 is 550kgs. Maybe treat it the same as you would an dedicated anchor winch, which would be to never load it with the windage/tide drag weight of the yacht, only the weight of the chain and a free anchor. For a small yacht 550kgs is quite a high load, but it could, when getting that stuck anchor out the mud, not doing your winch any good.

Also a Sheet winch load (for at least some make of winch) are intended to arrive on the winch from certain direction. So I suggest it worth checking the installation instructions if you are changing the direction of the winch load compared to how it was designed/installed.

I would guess it is not a problem for just winching the weight of the slack, or say 12m of vertical chain with a freed 15kg anchor on the end.

The suggestion to use the sheet winch to take in the warp section of the rode may well have been a daft one.
Having thought a bit more about it, best option would probably be first transferring the load to a stern cleat and then taking in the slack while motoring towards the anchor until the chain comes over the bow roller.

That said, I still find a maximum load of 550 kgs quite reassuring and the 'rule' of never exceeding the weight of of the chain and free anchor a bit over-prudent. (in your example it would be less than 40 kgs).

 

[Tranona]

Last year I finally put on a 10m of 8mm chain and 40m warp but didn't get round to using it. The main worry I have singlehanded is if in a tidal stream, I need to motor towards the anchor on tick over while being on the bow hauling it up. I hate the idea of overrunning the warp and getting it around the prop. So I would like all chain.

Highly unlikely your rope rode will get anywhere near your prop, particularly as it is in an aperture past a deeper long keel. If you go for a 30/30 or 40/20 mixed rode you will rarely actually use the rope - it is there for those odd occasions when you might want to have a greater scope.

Worth looking out for a secondhand SL Anchorman windlass - one of the best bits of kit I had on the old boat. It only comes with a 6mm gypsy as it was aimed at boats just like yours. No need to have the engine running. Just sit on the front of the coachroof and wind away!

 

[Stemar]

I've used a mixed rode on a similar boat for 18 years and never had any trouble with it. I've been anchored in 2-3 Kts of tide and not found it hard to pull the boat up to the anchor. I have had to motor the anchor out after a real blow, but it needed a lot more than idle. I reckon you pulling would generate far more force than an idling motor. The trick is to pull the anchor up until the bow dips, make off the rode, which by now is all chain anyway, then go back to the cockpit and drive the hook out, set a safe course on autopilot, then go to the bow and deal with everything.

BTW, following an illness, I found my 8mm chain and 10Kg anchor to be too heavy to pull in by hand, so I switched to 17M of plain vanilla 6mm chain plus octoplait. I can't imagine a circumstance in which the anchor would hold but the chain wouldn't be plenty strong enough.

 

[BabaYaga]

I've used a mixed rode on a similar boat for 18 years and never had any trouble with it. I've been anchored in 2-3 Kts of tide and not found it hard to pull the boat up to the anchor. I have had to motor the anchor out after a real blow, but it needed a lot more than idle. I reckon you pulling would generate far more force than an idling motor.

I have similar experience of using a mixed rode (20 +45 m), although I have not anchored much in strong current.
But I think the OP has a good point in his concern about the risk of getting the warp into the prop when the conditions are such that retrieving by hand is very hard.
Like this situation: Gale force wind, mixed rode of 20 + say 30 m out, single handed, no windlass.
With an all chain rode you could just motor to where you think the anchor is (or a bit further), rush to the bow and take in the slack, repeat....
With a mixed rode, I see a dilemma....
In such conditions I have sometimes tried putting the engine on idle with tiller centered, to give some support to the hand hauling. I does not work very well in my experience, because the boat already 'sails' a lot while the rode is being retrieved and the propulsion just amplifies this tendency.

 

[Neeves]

You do not need to run the engine to actually drive the yacht forward - it only needs HELP you pull the yacht forward - and if you get the balance right and you are not a skinny wimp like me the rode should never get near the prop as it will always be under slight tension.

You will also find retrieving a rode with 6mm chain is a real breeze compared to retrieving 8mm chain. The latter becomes increasing hard work, especially at 2am when you decide enough is enough and you will re-anchor somewhere more sheltered. . We use 6mm chain on a 38' cat and I have retrieved the old 8mm and the new 6mm and I have easily convinced myself which I really prefer. 50m of 6mm chain will 'only' weigh 40kg - something that is quite manageable stored in a milk crate amidships (so not in the bow) - so don't simply think of weight in the bow, there are other options. But pick up and carry 40kg before you make your decision about storing down below. A 50m rode is quite generous for a 24' yacht, considering you should be able to access locations that bigger yachts might not venture.

However note that if you have a mixed rode then the rope needs to have MBL greater than the chain (or I would as the rope will wear with time - so better if you start off ahead) and if the rope is as I suggest you will not get much snubbing, because it will not stretch under the low loads you are likely generate - so you will still need a snubber and one that you can attach to both rope and chain. Check carefully the rope you buy and make sure you can splice one to the other - or have the chandler do it for you. 6mm chain is very fiddly (and very difficult to thread a soft shackle through - I gave up).

You will have problems with shackles on 6mm chain as the recommended G209a Crosby shackles smallest size is 3/8th" - and that's far too big for 6mm chain. You will need to resort to standard Crosby shackles, which I think are designated G209? but I would suggest you buy a CMP Titan Yellow Pin shackle as the ones I have tested are grossly and consistently over strength and almost as good as the CMP Titan Black Pin shackles (that I do not recommend). CMP Titan Yellow Pin shackles I think are freely available (from chandlers) in the UK) - and the smallest sizes are quite small., at 1/4" WLL of 500kg or maybe a 5/16th" (with a 3/8th" clevis pin and WLL of 750kg - but maybe the latter is too big??) I think maybe Black Pin shackles only are stocked with the smallest 3/8th" - so they would not fit anyway. You do not mention what anchor you are using but remember the shackle needs to fit both chain and anchor (it might seem obvious - until you get it wrong) - so take your anchor with you when you buy the chain (and shackle) and make sure it all fits neatly, bow shackle, bow through shank). You mention that you are looking at Titan G40, they should also stock the shackles.

As an aside - when I was testing the Yellow and Black pin shackles I actually wondered if they were the exact same shackle with simply a different coloured pin.

The MBL of the chain you suggest will have a WLL of 25% (4:1 safety factor) and if you ever get near a tension in your rode of 450kg - you really want to be on shore.

I'd tend to focus my attention in terms of length of chain to thinking that most of the time you will use all chain, so what sort of depth might that involve and simply have the rope spliced on, or a simply eye ready to attach a shackle at the bitter end, and then you will only use the rope in the extremes. Chain sitting on wet rope is a recipe for chain corrosion and chain is much more easier to feed to a chain locker (or milk crate) than rope. So unless the weight will significantly impact performance go for slightly more chain. If you do as I suggest and focus on using an all chain rode then you will need some means to attach your snubber to the chain - and I'd suggest a stainless chain hook (NOT the Mantus hook) which again you should be able to source from the chansdler from which you get the chain and shackle.

I'm assuming you retrieve by hand - no windlass.

Jonathan

 

[TernVI]

I am still deciding what anchoring rode to carry on Paean. She came with 20m of 8mm chain which was OK for most instances but heavy in the bow.

Last year I finally put on a 10m of 8mm chain and 40m warp but didn't get round to using it. The main worry I have singlehanded is if in a tidal stream, I need to motor towards the anchor on tick over while being on the bow hauling it up. I hate the idea of overrunning the warp and getting it around the prop. So I would like all chain.

I am looking at 40 or 50 m of Titan G40 6mm. Weight in the bow is acceptable. However, it has a MBL of 1800 KG. Paean is only 24 foot but displaces 3T. My question is, does the chain need to be able to hold the displacement of the craft. I would guess not, as its the force of the craft moving through the water that matters. Thoughts?

A 3T boat can put an impact load of well over 3T on the chain in some circumstances.
A wave moves the boat and the chain stops it dead.
If you have all chain you will need a snubber to prevent this. If you ever anchor anywhere deep, you don't want to be lifting 40m of chain plus an anchor by hand. If you go to France or the CI's you will anchor in 20m+ at high tide. 10 or 15m of chain and plenty of rope is far easier and quicker to retrieve, and less weight in the bow.
If you need to retrieve a lot of rope rode using the engine against a lot of wind or tide singlehanded, bring it back to the cockpit and take up the bulk of it from there where you have control of the throttle. If it's not windy it's not an issue to whip up a lot of rope from the foredeck, because it's lighter you do it quicker and the time where the boat is not really anchored and not under control is shorter. That matters when you get crowded by other boats truning up in an anchorage.

 

[Neeves]

A 3T boat can put an impact load of well over 3T on the chain in some circumstances.
A wave moves the boat and the chain stops it dead.

Sorry - but I doubt this.

I'd like to see some data.

I tested our cat, 7t, at short scope 2.5:1, no snubber, and at 35 knot snatch loads the maximum tension recorded was 650kg. This was like driving the boat into a brick wall. I stopped the testing.

To record a 3t snatch load the anchor and seabed has to hold 3t - with out moving. I'd like to read of the anchor with this hold, for a 3t yacht, and the conditions under which these tensions are produced.

A 3t snatch load will break a G30 8mm chain. I'd like any documentation of chain failure - indicating that tensions of 'well over 3t' will eventuate.

Anchor threads appear to be focused at engendering fear and awe - not reality.

Jonathan

It was too important and I had to check:

But in the 2006 West Marine tests under 'perfect' conditions a 15kg Rocna held 2,500kg. Now to me a 15kg Rocna is a bit oversized for a 24' yacht (but then I don't believe in 'Bigger is better' nor that a 24' yacht will be subject to a 3,000kg tension on its rode). So to comfortably hold 3t the 24' yacht will need to carry a 25kg anchor (no safety factor) and to ensure the chain does not stretch, maybe 10mm G40 or 12mm G30 chain - and have plenty of it to deploy. The anchor is a bit of a problem as to engender safety you would really need to set this anchor quite deeply (as a shallow set anchor might simply be 'plucked out' and I'm not entirely sure where a 24' yacht is going to keep the power necessary to deep set the anchor, securely.

Tern VI - I think you got the decimal place located incorrectly - no issues - we are all human.



J

 

[dom]

A 3T boat can put an impact load of well over 3T on the chain in some circumstances.

What circumstances? ???

 

[Stemar]

I'm pretty sure a shock load of 3 tonnes would snap the Samson post on my 24 footer clean off.

In extremis, I want the holding of the anchor to be the weak point. At least a dragging anchor provides some resistance rather than allowing the wind or current to put me on the rocks while I'm still trying to get the engine started, and will allow me retrieve and reset it.

 

[Driftingby]

I am going through a similar exercise for my Sadler 25, I had thought to reduce from 8mm to 7mm, but from this thread am now considering 20m of 6mm which is twice the length of 8mm I have and porbably slightly lighter. I was then going to add 30m of octoplait for those occaisions I need more. Ths challenge I am now working through is how to shackle the anchor to the chain as anything small enough to go through 6mm chain will be way too small to through the anchor slot where I need something like a 15mm gap to get over the slot corner to outer shank corner distance?