Chain v Rope

[alec]

Is chain as strong as we think it is ?

I was surprised to learn recently that 8mm chain is worth about 2,500kgf.

Undamaged 12mm multiplait is worth at least 3,500kgf.

My own boat is at the smaller end of the spectrum with large overhangs. Unfortunately, this means heavier pitching . Also, my water supply is up forward.

In an effort to reduce weight, I would like to have less chain and more rope. I could also put this rope to good use when I occasionally visit marinas and dry out alongside walls and posts to antifoul and scrub off etc

However, I do realize that I may start to become a bit antisocial when anchoring.

I would be grateful to receive any views and comments.


Regards,


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[Mudplugger]

If you have ever been involved when the person on the foredeck has been dragged overboard by the anchor warp, then you would suggest that an anchor warp, as opposed to chain has no place on the foredeck.....It does NOT self stow.
for emergency use possibly,IMHO regards TW.

<hr width=100% size=1>Tony W.

 

[aitchw]

It's not a strength issue it's weight. The chain weight helps set the anchor and direct the pull more horizontally.

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[Joe_Cole]

My main worry would be the thought of the rope chaffing through on a rock or some other sharp object. I'm nervous enough when at anchor as it is!

Apart from that the extra large swinging circle would be a pain in the whatsit. (When I can I usually anchor close inshore..... laziness on my part...shorter trip to get ashore!)

You couldn't move some of the weight and re position things in the boat?

Joe


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[graham]

It all depends on the type of sailing you do .On my 22 footer I compromise with about 35 foot 8 mm galv chain shackled to 10mm 3 strand nylon.

One compromise I do when cruising is to put my spare 40 foot of chain in the bilge near the center of the boat this can be shackled on if any serious anchoring is needed.

Anchoring with all chain in deep water can lead to a very heavy lift when recovering it all without a windlass.

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[alahol2]

On our previous boat, a 32 ft cat, we used 6 metres of chain + 50 metres of 20mm 8 plait (I think that's what it's called). We anchor most weekends around the Solent and never had any problem with chafe. The 8 plait stows like chain, it just flops into place, I'd strongly advise using this over 3 strand which is a b****r to stow, you need to coil it and that's not what you want to do when raising an anchor.
The only downside is the amount of swinging room you may need, we ocasionally moored with 2 anchors if necessary.

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[Talbot]

the main problem on chafe is normally in the first 5metres from the anchor - thuis a lot of chain/rope isprovides a mere 5m of chain - too little imho, but 10m should be fine, however, I prefer 20m, because that is the part of the chain that is doing the most good in holding the anchor in place.

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[Talbot]

3 people in the room, there will be at least 4 different answers to this. A lot of multihulls use a mix of chain and rope. The minimum is always considered to be 5m of chain to minimise chafe on the bottom. 20m of chain provides a good catenary from the anchor to the boat, and provides the optimum for weight versus holding power, preferably with a slightly larger chain than you would use if all chain. Any more chain, and it can get very heavy to heave in. This will also miinimise any difference in swinging circle.

I have been using 20m 3/8" chain followed by rope on a 9m cat, but have just increased to 30m because I normally anchor in 8-10m of water, and have bought a windlass, thus can veer until the end of the chain! I have spliced this to 45m of 14mm octoplait to provide greatwer flexibility if needed.

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[Joe_Cole]

Agreed. That's just what I've got.........best compromise.
I'ld hate to have all rope though!

Joe


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[Soong]

Has a spool of cable ever been tried?

I feel sure its a terrible idea, but my mind wanders.

Soong

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[DavidTocher]

The strength of the largest shackle with a pin that can fit through the link of a chain is very low compared to either the chain or the rope. Most of the time I have enough chain but now and again might need to extend the anchor chain with rope. I'd prefer to have the long rope available for mooring alongside (e.g. rafting up)etc and not spliced to the chain. How do other people cope with this problem?

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[MainlySteam]

<<<20m of chain provides a good catenary from the anchor to the boat>>>

/forums/images/icons/blush.gif No, the catenary is only from the anchor to the end of the chain - the rope part of the cable can be considered to be straight and not contribute at all and only serves to lower the chain end of the catenary closer to the seabed so that the angle of pull is lessened.

John

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[MainlySteam]

Many work boats use wire rope as the anchor cable and have it stored on a winch drum. I have seen cruising yachts with their back up rope cable on a permanently mounted reel on deck for use when needed for anchoring or as a shore or other line (have seen the reel mounted about halfway along the boat so can be run out easily either fore or aft) - have to say that to my eyes it doesn't do much to the looks of the boat though.

No doubt the spool could be mounted below decks if one has the room.

John

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[MainlySteam]

If one uses an appropriate factor of safety for the nylon part of the cable (SF of 10 has been suggested to me) and use the maximum sized pin that will fit through the chain (normally, say, 12 mm pin will go through 10 mm chain) then I think the strength problem you outline mostly goes away. I add to the shackle strength by using a ss shackle and while many will say that it is bad to mix ss and galv I have never found it a problem on anchor cables with my own or other boats.

Regarding the other problem, we just shackle the rope part of the cable to the end of the chain, the rope part being spliced around a thimble, again using a ss shackle (we actually do this with a second anchor permanently attached to its own chain and to which the rope part is connected if needed, not the main anchor as the bitter end of its chain is permanently attached to the boat). I do not know why people go to the bother of splicing the rope part of the cable to the chain part except perhaps for looks - seems like a loss of versatility for a perfectly good piece of line to me.

John

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[Talbot]

Surely if you are lowering the end of the chain, and thus reducing the angle of pull on the anchor, you are also improving the catenary. But more importantly, you are also considerably improving the holding power of the anchor - and this is why I consider that 20m of 10mm chain + rope is a better bet than 40m of 8mm chain. However as I said in my earlier posts, this is a very emotive subject for which everybody has different answers, and this is my solution for peoples consideration.

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[MainlySteam]

Not making any judgement at all on whether chain and/or rope best. Just saying that the catenary ends at the boat end of the chain and does not extend up to the bow as you stated.

The rope is essentially weightless in water and will therefore pull approximately bar straight from the boat end of the chain to the boat (ie not in a catenary and certainly not an extension of the chain catenary). The angle that the rope lies at is that of the vector sum of the vertical and horizontal catenary forces at the boat end of the chain. As I said, the rope only serves to lower the boat end of the chain catenary closer to the sea bed thus making the angle of pull at the anchor lower than it would be if same short length of chain alone was used. As you say, this improves the holding power of the anchor, but only when compared to if the short length of chain alone was used ie the cable is much shorter.

The effect of this is clear if one considers an example where, say, the water is 15 m deep and the end of the chain is 5m above the sea bed with rope for the remainder, the anchoring effect is approximately the same as if you anchored in water 5 m deep and used the chain alone (I say approximately because in the mixed cable case as the boat rides back on the anchor the top of the chain will lift slightly as the chain catenary is pulled tighter, whereas in the shallow water chain only case the top of the chain cannot lift resulting in the extension of the catenary being slightly different).

John

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[Joe_Cole]

I thought that people spliced the rope to the chain so that it runs smoothly over the bow roller. On my boat (I have the rope shackled to the chain) it can be a nuisance hauling it in at times. My anchor is only 15kgs though so I can manhandle it relatively easily. With a bigger anchor it would be a problem.

Come to think of it I must try splicing it to see if it's any easier..........another job to add to the list!

Joe

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[Talbot]

About 8 years ago there was a very technical article in PBO about the forces on the anchor, and the effect of different chain/chain, chain rope, and rope only combinations, and unfortunately it has disappeared. As in most Cats, my anchor requirements are to get the best holding and strongest connection to the anchor for the lightest weight. I set this against a disbelief of the recommendations provided by the anchor salesmen which seem fine in normal conditions and then prove hideously inadequate at totally the wrong moment. The solution then fights with the rest of the equipment budget for priority! - so whats new /forums/images/icons/smile.gif

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[uforea]

I too used chain and octoplait and last year anchored in a favourite spot went below to start some lunch and 10 mins. later sensed and felt that something was not quite right. Looked out the hatch and found that the boat was now sideways to the current as the wind had blown the stern round. Went on the foredeck to sort it all out but found there was so much weight on the the anchor warp that I could not move it anyway. Sat there for 5 mins. or so trying to work out what to do next when suddenly the boat straightened up and drifted of downriver. Yes, a 10mm octoplait warp had been quietly sawn through on the front edge of my lead keel, which is very smooth with a large radius, so now I just use chain. So be warned you warp users, if you want a safe nights sleep stick to chain otherwise keep an anchor watch.

Ted.

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[MainlySteam]

I quite agree Mark and recognise the need to keep weight down on cats (including power cats, such as the powerful one I mention anchor trials of in my MoBo forum post on sea trials which, although a big boat, does without a windlass as well /forums/images/icons/smile.gif). 'tis always a compromise and a tricky path through the various claims as you say, many of which are pure myth.

Regards

John

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