Anchor Chain Weight

Discussion in 'Stability' started by Fanie, Jun 9, 2008.

  1. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    Tcubed,

    I have to disagree with everything you just said. Not only do I think your 'system' is dangerous, it creates a whole host of problems much worse off than a chain/nylon one.

    First:
    The reason for having a chain rhode is to reduce the angle that the anchor is being pulled on. This is the same reason for increasing the amount of scope you have out. Having a heavier anchor does very little to increase holding power relative to carrying the same amount of weight in the anchor.

    And yes in extremely heavy wind you can loose the cantenary effect of chain, but if proper scope is used, you still have a low angle of pull to the anchor. But the heavier the chain the more severe the weather it takes to have this effect.

    Secondly:
    The idea of using a floating anchor rhode is absolutley nuts. Now not only have you changed to one of the worst lines made for durability, you are actually reducing the effective weight of the oversized anchor you are suggesting to use. Just go out and see how much polypropaline junk it takes to float your anchor off the bottom, and in water any deeper than that you can't even get it down, let alone get it to bite.

    But you are right it will help get it off the bottom, since it is helping float the anchor up... You might as well use an inflatable lifejacket as an anchor line.

    Not to mention that under high loads Polypropylene line has been known to melt on rollers and chocks... just what I want from a piece of safety equipment that is usually the last line of defense between owning a boat and owning a salvage problem.

    Third:
    After ten years sailing the carribbean, and another 20 sailing in the states I have never heard or seen of a boat using wire as an anchor chain. The inherint limitations of wire basically are so great that there is no good reason to use it other than just to be different. Not only is there a corrosion problem with the strands, it has significant storage problems, as well as being prone to failure if it is ever kinked.

    A spool for a reasonable size wire anchor would have to be rediculously large to prevent to small a radius being bent in the wire, and the only good way to limit the amount of rhode out at a time would be to have a mechanical lock on the spool motor. Which if it every broke would absolutely prevent either bringing up or even controlling the amount of wire in the water.

    For my money I would always prefer a properly sized anchor with 300' of chain. However for smaller boats or where that much chain would cause bow weight issues I use 6-12' of chain with as much braided nylon as I would forsee needing based on the depth of water I travel. And when possible a second anchor of a different type for different bottom materials.
     
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  2. Tcubed
    Joined: Sep 2008
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    Tcubed Boat Designer

    I knew this would get someone worked up...

    <<Having a heavier anchor does very little to increase holding power relative to carrying the same amount of weight in the anchor.>>

    I find that sentence a bit confusing. Are you saying holding power is not related to anchor weight?

    <<And yes in extremely heavy wind you can loose the cantenary effect of chain, but if proper scope is used, you still have a low angle of pull to the anchor.>>

    So you are agreeing with me here. There will always exist conditions where the catenary is reduced to almost nil and you must use all the scope you would use with rope. But you have no stretch left in the chain. This is exactly how chain breaks actually, on that sudden jerk of the wind waves acting on the boat. I had an unpleasant experience in england, getting caught in an open bay with a storm coming. I did not get out in time, so i ended up trapped in there. At the time, i still had all chain. The surf zone grew out to the entrance of the bay. The snatch that developed in that chain must have developed close to one g longitudinal accelerations, so the force in the rode would have been approaching large fractions of the boat's total displacement in those instants. With the stretch of rope the peak loads would have been much less. This misadventure taught me a number of things including the limitations of using all chain.

    Your concerns about reverse catenary due to floating rope is valid, but in practice, the floating force of this short piece of rope is only enough to make a difference when there is no load. As soon as there is load the floating rope behaves indistinguishably from nylon. Think how significant a catenary effect you get from nylon is. Nylon sinks by about the same amount as floating rope floats. It ends up having an insignificant effect.

    You apparently despise the floating rope. First let me make clear that there exist very many different grades of floating rope. Some break apart very quickly, whilst others are remarkably durable. For example, I found a huge ball of hard, slick and dense floating rope on a beach once. It's colour was black. After untangling it all, i used it for years and it seemed like the stuff would never give up. You know if you can't trust it because it will have the typical broken surface strands, which appear almost immediately on the yellow kind, for example.

    I specifically said oversized rope near the anchor so it is understressed where it might encounter wear. This i do no matter which rope i'm using. Higher up it's important not to oversize because then it will not stretch as intended.

    If you haven't seen wire being used that is your personal experience. I have and have discussed at length the pros and cons of wire with those users, as well as using it. Your declarations demonstrate you haven't taken the trouble to actually sit down and work out the numbers. Wire is astonishingly strong stuff. You can fit a lot of it onboard very easily. And well galvanised steel is durable and dependable stuff. It lets you know, unlike SS, when it's ready for retirement.

    The stop on the spool can be arranged in a number of ways. There is no reason this would jam up if it is well thought out.

    Chain has certain advantages but for the type of sailing i tend to do it does not suit my requirements.
    In my 22 footer i carried 200 M of nylon + other rope, to anchor with and five anchors. Two anchors is not serious at all, no matter which rode you prefer.
     
  3. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    Tcubed,

    I hate the bloody chain also, BUT -

    Without it you are going to get whiplash, poor anchorage and short rope life.

    The boat must ride the chain, not the anchor, the chain is the buffer.

    All this has been discussed a few times, I suggest you do a search for it. If there was a better and more trustworthy way, everyone would switch to it right away. The chain works.

    Poor anchorage in good weather is of no concern, it is when the **** hits the fan that your boat could break lose and cause all other boats in it's path serious damage and even loss of life.

    If an anchor breaks loose, you may drift so fast with the wind that any anchor you put out may not reach the bottom.

    Don't bugger around with the wrong things ;)
     
  4. Guillermo
    Joined: Mar 2005
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    Guillermo Ingeniero Naval

  5. Tcubed
    Joined: Sep 2008
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    Tcubed Boat Designer

    Many thanks Guillermo on that informative link with plenty of numbers.

    <<Tcubed,

    I hate the bloody chain also, BUT -

    Without it you are going to get whiplash, poor anchorage and short rope life.

    The boat must ride the chain, not the anchor, the chain is the buffer.

    All this has been discussed a few times, I suggest you do a search for it. If there was a better and more trustworthy way, everyone would switch to it right away. The chain works.

    Poor anchorage in good weather is of no concern, it is when the **** hits the fan that your boat could break lose and cause all other boats in it's path serious damage and even loss of life.

    If an anchor breaks loose, you may drift so fast with the wind that any anchor you put out may not reach the bottom.

    Don't bugger around with the wrong things ;)>> quote by Fanie

    I've been trying to think hard about when i have dragged and the only time that comes to mind was once when we were forced to anchor in very deep (about 120 feet) water close to shore. The extremely steep drop off made things highly unfavourable for anchoring. We very quickly rowed out a thousand feet of line with the kedge and promptly pulled ourselves off the shore.
    That's my only memory of dragging in over 65 000 seamiles and many thousands of anchorages. I would say i'm not "buggering around", as that's a pretty favorable record.

    One of my points about chain is that there always exist conditions at which the catenary effect vanishes and you are obliged to hang additional weight on it (just like you must do always with wire).

    As for everyone switching, there are a couple things i say. One is that people are fairly conservative, on the whole, and will mostly do what they observe others to do. The other is that chain has its advantages, and these advantages quickly grow larger as the boat gets bigger, but for relatively small boats one must also know and understand what the disadvantages are.

    One of the reasons i like rope is precisely because you cannot get whiplash (see my little story previous posts) so i think you should try stuff before negating it.

    And finally, why do you hate the chain also?
     
  6. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    Heavy and uncomfortable to handle.

    Maybe your chainless setup works where you live. We have harsh seas here, the amount of wrecks could probably serve as an indication.

    I'm getting 2 anchors for my boat. If the wind comes up Ill tie one to .AU and the other to .ZA, see what gives ;)
     
  7. Tcubed
    Joined: Sep 2008
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    Tcubed Boat Designer

    <<<<<Heavy and uncomfortable to handle.>>>>

    Exactly. So we agree after all. And yes, typically the Caribbean is very nice weather, sometimes you get very nasty stuff though, especially when it's a full blown hurricane, but my sailing and anchoring has been all over the world, every ocean apart from the Pacific.

    And i strongly urge more than two anchors for anyone. I would feel very uncomfortable with just two. You lose one and now you only have one anchor! Not good.

    Five is; Storm anchor, two working anchors plus a spare (ideally all different type too) and the kedge. It is the best value insurance money you could ever spend on your yacht. Don't skimp.
     
  8. Tcubed
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    Tcubed Boat Designer

    Now i've been looking at the site, Guillermo, and Fortress says:

    [FONT=Arial,Helvetica,sans-serif]<<<<They also state the following: A “Lunch Hook” should be able to hold your boat in a 15 kn breeze. A main, or “Working Anchor” should hold up to 30 knots of wind. A “Storm Anchor” is for winds up to 42 knots.>>>>

    [/FONT]On the basis of that it is no wonder that they claim such light weight anchors will do.

    Here would be my definitions: lunch hook- max 20 knts, working anchor- max 60 knts, storm anchor- max 160 knts. Assuming you're in protected waters where the fetch is less than a mile.

    I'm not criticizing the site, just Fortresses' standards...
    [FONT=Arial,Helvetica,sans-serif][/FONT]
     
  9. Guest625101138

    Guest625101138 Previous Member

    I got annoyed with stuffing about with rope and chain. Ended up with all chain. I carried 100m of 1/4" galvanised chain. The galvanising begins to flake after a year or so but the chain will last a few years. If I was doing it today I would just go for all stainless. Probably get enough for around USD1000 and it will last for ever i.e. my lifetime.
    http://www.stainlesschains.net/
    Best insurance you can buy.

    There is one risk with it. If you anchor in really deep water you will need a winch to pull it up or a couple of strong men. Work out the dead lift before you anchor and make sure you have a means of retrieving it.

    The advantage is that it works anywhere and if you are in doubt about the bottom don't even bother with the anchor. I have spent comfortable nights "anchored" on gravel bottoms with just the weight of the chain doing the job.

    I never got the chain stuck in reef to the point that I could not get it off by motoring. Once I went to all chain I never again got up in the morning to find a rope wrapped three of four times around the keel, drive leg and rudder. Rope that floats is a nightmare in slack water and that is the ideal anchorage - every zephyr of wind can give another turn around the keel and rudder. If the wind then comes up it is an absolute nightmare trying to release the turns. You can be held bum to breeze with the anchor hitched to the rudder. (I cannot believe I am the only person who has been through this because it happened more than once.)

    Stainless is clean and easy to clean. There is no flaking of zinc. Some of the stories about corrosion cracking have to be taken with a grain of salt (pun intended) because for a pleasure craft how often is the anchor actually used. If you are really concerned about salt on it then hose it off before it is stowed.

    So I guess this is the lazy man's approach - no complication. On the other hand, have a look and see how many ships use a combination of rope and chain to anchor. There has to be a message there.

    Rick W
     
  10. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    on using all chain.... certainly do so, but then put on a length of nylon the same length as the boat, use a hook, and slip it into the chain as it nears its end. The nylon rope then does all the work, no more chain snatch, no more noise from the bottom transferring up the chain, and certainly no broken chain from massive snatching either.

    Use a small diameter nylon, nylon stretches twice its length before it breaks, so there is much room to allow stretching, and by using a light line the action works better.
     
  11. Guest625101138

    Guest625101138 Previous Member

    Yes good advice. I should have mentioned that in heavy weather I shackled to the chain with rope that came back to the sheet winches. I never had a lot of faith in the cleat at the bow. The rope went over the bow protected by rubber tube as a hawse provides on larger vessels.

    Rick W
     
  12. Stumble
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    Stumble Senior Member

    I think I left a mistaken impression that for a boat that was expecting to achor regularly I would consider two anchors enough. We normally carried four on board; A large all chain plow, a large fortress on all chain. Both carried on the bow roller. These were the two primary anchors and used in almost all conditions. There was also a backup plow and Fortress stowed where they were available but not in regular use. But with 450' of chain/nylon attached. This is in addittion to the kedge and the anchor used on the dinghy which could also be used as an aditional Kedge if needed.


    And Landlubber thanks for reminding me of that trick for taking the shock load off of a chain rhode. I use it, but forgot to mention it.

    I still stand by my problems with useing floating line for an anchor rhode. I just see you on one side recomending using a heavier anchor and on the other side suggesting using a positively boyant line to attach to your boat. To me this is strangely counter productive. I am really not sure what the density of polypropylene is, but even it can only float 1 ounce for every foot, dropping anchor in 30 foot of water now reduces the weight of your anchor by 300 ounces or 16lbs. Now of course a lot of this rhode would just be floating on the surfance, but in the same type of conditions where your chain has lost its cantenary effect of chain you have also lost the inverted cantenary of the polypropylene. Meaning that just when you need your anchor the most it is at it's least effective.

    Plus all of the tests I have read indicate that the lower the pull angle between the boat and the anchor the better the holding power, and the more likely the anchor will reset if it breaks free. In my mind if a chain rhode anchor does break free it is more likely to reset since the weight of the chain is working to reduce this angle. The floating line again has the exact oposite effect, that of increasing the angle between the anchor and the bottom when it is trying to reset.
     
  13. Nigel1
    Joined: Nov 2007
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    Nigel1 Junior Member

    Just my 2c's worth concerning anchors, chain. wire, rope etc.
    I work as a skipper of a high horse power (20,000hp) anchor handling tug, capable of working oil rig anchors in water depth in excess of 2000 meters.

    Rigs typically use small anchors in relation to the displacement of the rig. A typical oil rig is held in position with 8 anchors, and the typical weight of each anchor is 10 to 20 tonnes, with a loaded up semi submersible rig having a displacement in the region of 30,000 tonnes.
    The anchors typically used are either Vryhof Stevpris, or Bruce Twinshanks.
    Virtually all the rigs use a long scope of chain, typically between 500 to 1000m of either 87mm or 100mm (3.5inch to 4 inch).
    Every rig owner would love to substitute a bigger anchor for the chain, chain is expensive (and in short supply), however, all mooring tests indicate that a bigger anchor with less chain will not hold. Vryhof claim that their stevpris will withstand an upward pull of about 25 degrees above the horizontal, although all the mooring analysis for this type of anchors uses zero degrees, and enough chain is laid out to achieve this.
    For the really deepwater stuff, typically a very long length of 90mm diameter wire is used.
    One way the rigs can avoid using long lengths of chain and wire is by the use of what are known as vertical lift anchors (these cost big bucks). These need to be prelaid before the rig is at location, and are designed so that a vertical lift component causes the anchor to dig deeper into the seabed. They are designed so that with the use of shear pins, the mooring wire can be pulled back in a direction opposite to which the anchor was laid, and this allows the anchor to re-orientate itself and comes out of the seabed backwards. The disadvantage is that the gear is expensive, and takes longer to moor up the rig
    Polyprop ropes are also used in deepwater moorings, these may be about 160mm diameter, are very expensive, very prone to damage, and need anchor handlers with very large winches to accommodate the require lengths of rope.
    The one big problem with using wire as mooring (not so much with a rig which tends to excert a constant tension on the moorings, is that wire which is subjected to loads in excess of 50% of the breaking load are irreversibly damaged. These loads can typically be caused by snatching the wire in a heavy sea/swell. Unless the wire is very very carefully examined, and you know what your looking for, this damage is very difficult to detect.

    On my smaller boat, I use as much chain as I can handle with about 30 foot of nylon between chain and boat. If seas and swell are reasonable, I will consider transfering the mooring to the stern, as this boat lies a lot more confortably that way, with minimum yaw

    Have a safe trip

    Nigel
     
  14. Guillermo
    Joined: Mar 2005
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    Guillermo Ingeniero Naval

    In my opinion, only a couple of boat lengths chain (at its most) is really necessary for usual shallow water depths, to increase the weight of the tackle at the bottom, avoid chafing and help reducing the working angle. Behind that I prefer to use a long, good quality and well sized rope. This also reduces weight aboard.

    For deep waters a longer length of chain and less rope is desirable.

    For a thorough justification of this, I recommend the reading of:
    http://alain.fraysse.free.fr/sail/rode/dynam/dynam.htm


    Cheers.
     

  15. Fanie
    Joined: Oct 2007
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    Fanie Fanie

    I got my anchor chain today. 10mm x 10m times 2. He he, the wife picked it up :D She commented on the weight when she got here, they had to load it in the car for her :D The weight is quite a bit, but one (male) person can still handle it.

    Galvanizing may wear off after a while, but it is cheap to send it in and have it hot dipped again. I can live with that. Seeing that I'm not going to be permanently on the water, I'm sure it will take a while.

    The anchors are being laser cut, expected to arrive any day now. I'll weld them up and test, if I'm happy it will get hot dipped with the chain. Find a builders heap of sand and see if the car can dig it in there. Wonder what the builder is going to think. I'll tell him I'm working on a new type of car brake :D


    Winding the anchor rope on a spool or bobbin, is this a problem with the rope's stretch or not ?
     
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