Chain v Rope

[duncan]

early you ondicate that you have 20m 3/8ths chain attached to it so you have 45kg hanging of the bow when anchored on 20m plus - that is some weight to manhandle!

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[Joe_Cole]

I must be stronger than I thought!

In reality, I invariably anchor close inshore so the anchor is still on the bottom when the shackle gets jammed on my bow roller. Mind you, your comment makes me all the more convinced not to anchor in deeper water /forums/images/icons/smile.gif

Joe

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[TonyMS]

We use 15m of chain on our cat. With a light Fortress anchor, it is easy to manage and usually holds. If there's a problem, we set a second anchor (CQR), also on a chain/rope mix.

We'd previously had a shorter chain, and it didn't do the business.

I'd appreciate authoritative instructions on how to splice rope to chain. The shackle we use at present always jams in the fairlead.

Tony

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[Joe_Cole]

Depends on the rope, but if you get hold of the Jimmy Green catalogue there's a well presented section on making the splices. It may be on the web, but I haven't looked.

Joe

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[aitchw]

I think instructions are also on the Marlow site.

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[duncan]

Re: Chain / Rope Splice

best instructions out there seem to be here <A target="_blank" HREF=http://www.bluemoment.com/warpchainsplice.html>http://www.bluemoment.com/warpchainsplice.html</A> - covers both 3 strand and anchor plait (seperately!)

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[duncan]

Joe - As I fish a fair bit and have a drum / gypsy windlass I thought I would go up from the 4m / 8mm chain I had as 'standard issue' to 30m of chain. Unfortunately the winter cod grounds of the south coast are around 30m deep and this means that I have to swap the thing from the drum to the gypsy with the full weight (55kg) at times. Yes I can take the load on a chain hook etc but it's still hassle and highish loads (sometimes with 2 knots of tide and the hook still embedded......)
I have gone back to 15m and this seems to be a good balance - I have not noticed any difference in holding and use the same overall scope. OK I use the thing in 15m of water ocassionally too but the conditions for this tend to be calmer / warmer and less tide so I win all round.

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[alec]

I read your view on catenary and maintained pull angle with interest.A piece from Bernard Hayman ( anchoring guru) comes up with a surprising suggestion for ‘all chain’ length compared to depth .

As follows :-

At 2.5m depth 8xdepth of chain
5.0 m " 5.5xdepth "
10m " 4.25xdepth "
15m " 3.5xdepth

I think the shallower depth suggestion will surprise many of us.

Interestingly, after investigating 7 cases of chain breaking whilst at anchor, he is a very strong advocate of including nylon rope when anchoring. He cites the example of being able to snap cotton with a sudden jerk where a constant pull makes it very hard to break.

Sudden jerks appear to be chain’s weakness but the introduction of nylon will provide the essential absorption of energy. I have read a number of cases of Blue Waterer’s who tend to stay with their yachts in a big blow at anchor put this down as a very important factor. They see many cases of boats around them failing when there is no rope to take the jerking. I have no idea however how much rope to include.


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[MainlySteam]

I believe that the quoted "chain length versus depth" recommendations are technically correct and we follow similar recommendations. For example, we normally anchor in 20m with around 3x scope of chain and have successfully weathered sustained high end of Force 9 in a mud bottom when doing so. Cable lengths greater than those quoted for various depths are obviously necessary if part of the chain is substituted by rope.

In my opinion one should keep in mind that nylon has its difficulties under cyclic loads and is also susceptable to chafe, twists in the lay, etc which also affect its strength.

I have never experienced snatching with an all chain cable and we have never felt the need to use any nylon to absorb shock loads. This includes conditons of heavy gusts of 50 - 60 knots with a low average wind speed of perhaps 20 Knots. Even in very heavy gusts and sustained wind I have never seen our anchor cable pulled anywhere near to straight such that a shock load was possible (if one does the trigonometry the chain enters the water a long way in front of the boat when that occurs if one uses the scopes, say, that are quoted from Hayman), and another forum member whose sound experience I trust has reported the same. No doubt that it happens with light boats in shallow water with light anchoring gear or short scope or with heavier boats with gear undersized for the boat and conditions but that is a fault of an insufficient anchoring system not an inherent fault of the type of components within it.

Putting aside things such as degradation due to corrosion, fault in material, etc I would be surprised if the chain in a chain cable has ever failed under snatching loads except in the case that it was undersized for the boat and conditions, which of course, would be tempting failure no matter what material was used. Because of the unpredictability of the performance of rope, much higher factors of safety are demanded of rope rodes when compared to chain ones in their design.

Note that I have no desire to push chain, I agree with Talbot that in many cases for best anchoring result when deadweight carrying ability is limited eg catamarans and race boats, that rope is a good choice.

John

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[duncan]

planning hulled powerboats in the range 7 - 15 metres will snatch very easily when at anchor in many conditions (I would expect the above to apply to longer vessels as well but do not have first hand experience. I believe this is a combination of lighter weight relative to waterline length and windage plus a greater relative rigidity along their length - ie the bow doesn't dip as easily as, for example at the other end of the scale a full length keeled yacht. Even light gusts of wind, small waves or wash will send a strong judder th rough a boat anchored on all chain without any damping.
This is especially true in very shallow water as you highlight, but even with scope in the region of 6-8x.

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[MainlySteam]

Hi Duncan

When I referred to not experiencing snatching I was referring to my own boat but I see that I did not make that clear. I have experienced it in planing hulled powerboats, just as you say - would add to your comments that all planing hulled powerboats I have been on (including bigger ones) have had comparatively light anchoring systems though, perhaps partly (as well as avoiding deadweight) on account that they usually cannot stand or are not expected to stand the more severe conditions expected of a cruising yacht.

I would suspect that sailing cats suffer the same way, but could not comment from experience - perhaps someone can?

John

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[hylas]

There is a very interesting and hightly technical Web page on this subject:

http://alain.fraysse.free.fr

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[Guest]

Catenary / Rope / Chain ....

Catenary is from point of exit from boat to point of joint to anchor irrespective of angle / curve ...... which can be zero to al;most veryical to sea-bed then horizontal ..... etc.

The original post asks whether rope or chain / mix etc.

As many time before this subject has led to many opposing / varied replies ..... Hylas with his rope only and me with chain only ....... the 'in-betweenies' are numerous !!

I use only chain and when I need a quiet time - hang off the last metre of chain on a rope warp to stop the grate / scrape noise of chain in stemhead fitting. As to using only rope ..... sorry - maybe for a quick stop to fish or grab a sandwich .... go to sleep on a rope scope ???? Never.

<hr width=100% size=1>Nigel ... and of course Yahoo groups :
http://groups.yahoo.com/group/gps-navigator/

 

[MainlySteam]

Re: Catenary / Rope / Chain ....

Hi Nigel

While I think from past posts we are in pretty close agreement in the anchoring department I am driven /forums/images/icons/smile.gif by a high level of pedantry /forums/images/icons/frown.gif to point out that an elastic cable (eg nylon) does not form a catenary under the influence of gravity.

A cable has to be uniform, non-elastic and (infinitely) flexible to form a catenary. So an anchor cable made of two different chain weights does not form a catenary either, but each section of chain in the cable does form its own catenary. Nylon never forms a catenary and especially does not do so once it is loaded.

Trust you will put up with me seeing as it is another slap in the face for rope /forums/images/icons/blush.gif.

Regards

John


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