Wire Rope Anchor Rode

>It is not however a failure of weight, for as mentioned by a previous poster the catenary effect of a chain is near zero when the chain is tight<

It is fairly unusual to get a chain bar tight as the wind force must be extreme , unless the chain is way undersized .

For most folks the usual 3 strand nylon selected for the wind expected is best , with a few ft of heavy chain .

The problems I have seen with Nylon is folks using a way too large diameter for mere overnight use.

3/4 or 1 inch inch may be fine for a 40 ft sailboat in a big blow , but nylon requires a load of about 15% of its breaking load to begin to stretch, and most overnight anchor loads are minor.

1/2 line or so would do better at providing a good ride for a boat that dodges at anchor ..

A docile boat can simply use a rode rider weight , as the light line eats surges.

 

Yes indeed a docile boat can sit happily on a chain only (assuming an anchorage sheltered from waves (or long enough scope to allow for the wave peak) and the force of the wind is insufficient to pick up all the chain to the anchor to alter the angle of the rode sufficiently to reduce the holding capacity of the anchor, but as I alluded to in my last post any boat can anchor easily if it is calm conditions and the scope is sufficient, I have myself anchored on chain ONLY (anchorless) before, knowing that it would not move because the friction and weight of the chain was greater than combined force that the wind and current acting on the boat. But that isn't when anchors fail, nor when rodes fail.

Most times, and in crowded anchorages I anchor on only chain, this is because 1, I am lazy and 2, that is what most people do and to keep the swing of the boat the same as the boats around me I always try to have a similar rode (if I think it is safe to do so) that we turn in a similar fashion to avoid collision when there is insufficient room to allow a complete turning circle of the boat around the anchor without overlapping my "neighbours" turning circle.

However all this is on a calm day, current is never really an issue normally.

But on a calm day any muppet can anchor with a shoestring and a lump of lead. The day to think about is the day you feel the wind pick up, or in fact the worse day you could ever expect, because that is the day the anchor could be plucked out of the seafloor and bad, bad things can result.

On that day your catenary can, and will become bar tight and even the best anchor, properly sized, will be dislodged if the rode cannot maintain the right angle and ideally some shock absorption, btw, the shock absorption doesn't have to be much, and in fact I've found myself that in very bad weather Nylon is actually too stretchy for my boat (the COE is forward of the keel on mine and it will horse if given too much spring in it's rode!) so polyester is preferable for LONG rodes, and is much cheaper and abrasion resistant an easier to handle.

I normally anchor in 2-5 meters but with tide that can be 10 meters and in the worst conditions I would need a 7/10-1 rode so 100 meters of poly rope is called for. Actually Rocna recommend Poly for these reasons and while I took some persuading an experience last year that required I have a very long Nylon rode caused me to rethink the suitability of nylon, but for short rodes, by which I really mean the snubber it is superb.

Rocna and others also suggest rubber or other snubbers as options and I'm sure they are suitable but I've no experience and the sizing of the snubber to the weather would be more challenging than with a rope I think (with rope it is simply a matter of choosing the type; poly or nylon; the diameter; and the length. With these three variables and even a very few snubbers (according to the expected forces acting on the boat) it is easy to see that your adjustment options are very flexible indeed).

You mention combined rode and I think that is the best solution and is recommended by Fortress, Rocna, and in the books and online resources I've read, and in theory offers the best combination of rode, without going into unusual rode options (which I don't include wire rope except as a leader).

You mention rode rider weight, do you mean an angel (kellet), if so I used to think they were a good idea but actually they only really work for an all chain rode (using one with rope could take it to the seafloor resulting in chafing) my own pet theory is that an optimised rode would include a wire leader followed by a weight (essentially an kellet permenantly attached; or that could be lowered to the anchor end after setting the anchor) - a short chain and then a rope rode. But I have not tested this and would need to get advise too.

One other thing is that I would always keep the chain rode complete to the boat in an anchorage and have the rode terminated in a rope snubber but in the event this snubber failied (being cut by a propeller or severe chafing) the chain is there to take up the resultant `slack` ;-) Actually with all rope rode I usually deploy a primary and secondary that has a meter or two of slack, but I'm WAY over cautious and I don't have a large motor to get me out of problems that most cruisers have available if the worst happens.

As for oversizing I think you make an interesting point, but this is where the snubber comes in again, a fairly rigid poly line can have a nylon snubber from the chain if you have a long enough snubber (or long enough chain), having more than one snubber (or possibly snubbing device) to match the expected loading allows you to `tune` the rode elasticity to the conditions. Once conditions deteriorate sufficiently that your snubber is too short (I think a snubber up to 30meters is normal but I realise that might be an alien concept (btw the option to buoy the snubber if the conditions suddenly deteriorate in order to lengthen the rode without first shortening)

The only problem with this is when leaving the boat for sometime when the conditions could weaken and allow the rope rode to chafe, and this I think explains the popularity of mostly chain rodes in shallow anchorages and average conditions, but this is not so much optimisation and realism

One thing to remember is that the forces on the boat side of the rode are much greater than at the anchor and rope can chafe so having an oversized rope makes a lot of sense, by oversized I mean more than you would need for the maximum breaking force expected on the chain, `trashing` a 100 meter rope because of >1mm of chafe could be an expensive way to sail but would be necessary if the rope was sized exactly to the load (if that were possible in practice).

I cannot comment on the exact thickness you mention, I have no experience of that size vessel and I'm no expert but building on what I already said and to agree with you point I would suggest having an oversized main rode and a thinner rope snubber to allow the required elasticity, that way you have the bigger rode deployed already if the conditions deteriorate and don't have to re-anchor, and the smaller (much cheaper and more replaceable) rope takes the chafing.

That's probably way too much info and opinion but it's my two cents (actually 2 penny's worth as I'm English!) for what it's worth (less than 2 cents perhaps! ;-)

 

In shallow water you chain indeed pulls bar tight. The only chain ive broken was a shallow water anchorage. Deep water drs give plenty of catenary, shock absorbing , but the cantenary stores so much energy when tight in the gust , that it launches the boat forward in the lulls .

Very much veering , but less shock loads with a deep water set ...20 metres deep with 100 plus meters set.