New anchoring system thoughts

Discussion in 'Boat Design' started by Stumble, Mar 14, 2012.

  1. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    I have been kicking around the idea of completely changing my anchoring system, and would be interested in people's thoughts.

    Fundamental premise: an anchor systems holding power goes up faster with increased weight in the anchor than weight in the chain.


    The idea is to replace my 60lbs or so CQR and 300' (1200lbs) of 7,000swl/28,000lbs breaking strength chain with a much larger 150lbs anchor, and 1/2" amsteel blue line (30,000 min breaking streingth). The total system weight would drop by more than a thousand pounds, and at the same time increase the maximum holding power of the system. I would also replace a standard windlass with an electric self tailing winch, possibly with the new Harken rewind radial winch (reversing).

    Of course this would reduce the abrasion resistance of the chain, but I think the amsteel would be fine given that the boat would never see anything but mud and perhaps sand bottoms.

    Let me know what you think.
     
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  2. nimblemotors
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    nimblemotors Senior Member

    If you reduce it by 1000lbs, it would make it weigh less.
     
  3. Frosty

    Frosty Previous Member

    Sigh---such is the art --and I mean art of anchoring. the size and weight of the chain is just as much important as the anchor.

    If the weight of the chain does not pull the anchor flat with the sea bottom it will pull it up and trip it.
     
  4. Stumble
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    Stumble Senior Member

    Frosty,

    The concept comes from a number of places, but fundamentally from the combination of two charts...

    The first http://www.nsw.yachting.org.au/?Pag...orts~_q@a/21893/37545/,2010_Reports/22623/0/0 details the maximum holding power of a number of different weights of the same type of anchor. As it shows, the max holding power goes up significantly faster than we're the same weight spread out over the leingth of the rhode.

    Secondly is http://www.coastalboating.net/Cruising/Seamanship/Anchoring/KelletFacts.html which indicates the holding power loss from different scopes. In line with this chart a scope of 4:1 will only provide 55% of the theoretical holding power of the anchor, while a scope of 10:1 will give 85%, thus confirming the old notion that more scope equals more holding power. But if you have ever seen all chain rhode in a blow, you will notice that it is bar tight, which precludes any advantage of weight, since there is enough force to lift the cantinary anyway.


    The concept here is not to eliminate the weight, but to move it to the place where it is most effective, which is the anchor itself. Though some practical limitations do limit the maximum size of the anchor, by the time we reach this point, the anchor is so outsized for the boat maximum holding power should be effectively unreachable.
     
  5. masalai
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    masalai masalai

    Is not boating all about compromises and such? Just do it... each situation and occasion has different considerations. - - - No need to establish a system for a quiet overnight stay, by laying out for a full gale and changing tidal flow and wind directions... Do what is appropriate for the occasion and be prepared to adapt as needs change...
     
  6. PAR
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    PAR Yacht Designer/Builder

    The best anchoring system I've seen was a heavy anchor (multiple choices), but instead of chain or rode, galvanized 7x19 cable was used. The cables (there were two separate systems) were wound on drums, each under the aft portion of the V berth. They were motor driven, but also could be hand cranked with a reduction gear and crank. The cleverest damn setup I'd ever seen, no muss or fuss. The cable fed through a heavy wall conduit, exiting aft of the roller, running through a stout fair lead to keep it from dancing around. It even had a built in wash down as the cable came aboard, which hosed and brushed it before entering the conduit. Next time I get a big cruiser, with the forefoot volume, I'll consider this upgrade, as it's a lot lighter then all chain. The only complaint I had was the noise during deployment and recovery. The cable slapped around in the conduit making a terrible racket, but one that could be lived with, considering the cost, durability and security it offered.
     
  7. michael pierzga
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    michael pierzga Senior Member

    You would like to eliminate the chain ?

    I dont like rope anchor rode. To difficult to handle and stow , difficult to clean off the mud , in certain conditions the rope , since it doesnt sink fast , gets caught around the keel of a sailboat or other yachts catch it. .

    To best utlize the weight of chain get it out of the bow of the boat and move aft near the keel.

    For a secondary anchor , rope works because its practicle. Investigate lead core rope.

    Batsystem of sweden markets a very nice capitve rope winch for handling anchor rode on small craft. It is commonly used for stern set anchors in the north countries where yachts anchor bow to the rocks to protect the rudder.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    It does depend upon class requirements too, if the yacht is to be classed. The size of boat and the anchor winch size play a part. You can, if allowed substitute chain with wire, we have before, but some Class societies still insist on chain even short lengths between the anchor and the wire or warp, typ. 20% of the boats length.
     
  9. DCockey
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    DCockey Senior Member

    Why Amsteel Blue and not nylon? Do you consider less stretch desirable in an anchor rode?
     
  10. Lister

    Lister Previous Member

    I Google it:

    Amsteel Blue Line
    Features:

    Stronger than wire
    Same elongation as wire
    Extremely light
    Highly abrasion resistant
    Non-rotational
    Class 2 12-Strand splice
    Stronger than AmSteel
    Much stronger than steel
    Very low stretch
    Easily spliced
    Superior flex
    Torque free
    Uses Dyneema SK-75 HMPE fiber
    A size for size strength replacement for wire rope at only 1/7th the weight
    Torque-free, very flexible, easy to handle
    Similar elastic elongation to wire rope
    Easily inspected or field spliced
    Floats
    Fatigue and wear resistant

    Quite something!
    I suppose they have several Amsteel, I Google the Blue Line.
     
  11. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    Isn't this stuff kinda slick? You may want to look into how well a winch as described would grip the wet line with mud and possibly weed on it. If there is room on deck a reel winch might be more practical.
    The flotation qualities would make a kellet a good idea to keep the rode from being fouled by other boats.
    I do agree that one kilo of anchor provides much more holding power than one kilo of chain.
     
  12. Submarine Tom

    Submarine Tom Previous Member

    Stumble,

    Anchoring is a multi facetted endeavor. There are entire books written on the subject.

    The nature of the ocean floor (where anchoring) is a huge variable. If it is penetrable (sand, mud, shale, etc) then I would adamantly disagree with your premise that anchor weight is more important than chain weight. I would argue the opposite is true.

    An often over looked variable is sufficient scope to set the anchor (or to even bother setting it at all!). Once set, scope can be somewhat reduced.

    Have you considered tandem anchors in series?

    -Tom
     
  13. murdomack
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    murdomack New Member

    You could have a short length of heavy chain straight off your larger anchor. It would set and hold better but may give you problems when getting it all back on board. I'm sure you could find a simple way though.
     
  14. Stumble
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    Stumble Senior Member

    Mile hog,

    It is very slippery, actually even more slippery than Teflon. But it works fine on winches, though you typically need an additional wrap or two.

    Dcockey,

    Honestly I don't consider stretch an advantage. A lot is made of it, and for a lunch anchor it does help, but in storm conditions the stretch creates friction, the friction creates heat and abrasion, and the heat can be high enough to melt the line. This is actually the failure mechanism of my dock lines during Katrina.

    In addition the problem with nylon is that is looses a significant amount of strength when wet, which means it has to be sized to take this into account, requiring much larger line than desirable otherwise.

    Submarine Tom

    I have yet to see any report that indicates that an additional pound in chain generates more holding power than an additional pound of anchor. If this was true, why even use an anchor at all? Just drop a few hundred feet of chain an don't mess with the anchor.


    Murdomack,

    If the goal was chaff protection that might make sence, I am not seeing the value though otherwise.



    I want to point out that while I am defending the idea, I am not convinced of its effectiveness. I am just trying to make reasonable responses to criticism to keep the ideas flowing.
     
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  15. michael pierzga
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    michael pierzga Senior Member

    If you must go rope to hydraulic winch,.... the most successful race cruisers Ive sailed ,with rope anchor rodes , used a cockpit mounted hydraulic. The cockpit winch saves weight and money because it is multi purpose and it allows the helmsman to single handed retrieve the anchor and drive the boat.

    A high speed winch ratio is best. Electric motors don't like long...75 meter sheet pulls..they overheat.
     
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