Anchoring in heavy conditions

Discussion in 'All Things Boats & Boating' started by Patrick BLOSSE, Nov 1, 2013.

  1. Patrick BLOSSE
    Joined: Mar 2007
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    Patrick BLOSSE La Terre entière.

    Hello to all,

    Considering the title, I am searching for the proper up-to-date literature taking into account the latest calculations about forces - and overall, energies and powers - encountered dynamically by our boats at anchor (in reasonably sheltered areas) against the winds and the seas.

    Through so many testimonials, the breaking consequence on the lines, either all chain or mixed, put fondamental questions about the weakest link, which can be so different from the deck to the bottom.

    I red with really great benefit the following calculating sheet produced by Mr Alain FRAYSSE: http://alain.fraysse.free.fr/sail/rode/rode.htm

    Thanks in advance for contributing.

    Patrick
     
  2. michael pierzga
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    michael pierzga Senior Member

    The weak link for me has always been the anchor chain . Windlass and chain stoppers have never failed.

    The failure of the chain occurs when a sloop rigged boat tacks back and forth at anchor in gale condition.

    Boat speed may be greater than one knot before the boat comes to a stop. When the chain pulls tight , these repeated shock loads breaks the chain.

    Areas with powerful katibatic winds are also chain breakers.

    For a sloop with all windage forward, a riding sail aft is of some benifit..

    Deep water anchoring is also a benifit in that the chain catenary provides a shock absorber.

    My recent chain break was in shallow water, powerful katibatic wind

    Ketch rigged boats dont suffer as much from tacking at anchor
     
  3. Patrick BLOSSE
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    Patrick BLOSSE La Terre entière.

    Michael,

    Thank you for your answer and be kind to consider my relocation in the "Boat Design" area, as a more adequate thread.

    I do look for calculation and engineering subjects especially around your really important point of vue about dynamic conditions, to be calculated as critical additionnal conditions.

    See you upper please in the "Boat Design" area.
    Kindly.

    Patrick
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Sizing ground tackle and it's related equipment is easy enough. I'd agree that the rode is the usual weak link or at least a portion thereof, like a shackle.

    Safe anchoring I think is often subject to technique and anchorage luck, then equipment. Sometimes you just get what you get, as you duck into a cove or other assumingly protected area, just to have the wind, current and tide conspire to piss you off. With some experience, you can avoid 90% of the bad spots and techniques can help with the remaining.

    What precisely are you after? Is there a tackle sizing issue you'd specifically like to answer?
     
  5. michael pierzga
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    michael pierzga Senior Member

    Hard to carry oversize ground tackle. Weight and physical bulk. When you go one size bigger. Say from 10 to 12 mm you end up with a shorter chain in the box.

    Chain swivels are the weakest link in the system. Read the directions that come with the swivel and install as directed.

    Its difficult to tell what the working life of a chain , swivel, shackle is. Frequent inspection is your only defense.

    Ss chain is beautiful but it rapidly developes stress cracks. Be aware that just because it is bright and shinny is not an indicator of reliability

    The anchor roller assemble is an important component of the system. If the roller fails or if the chain jumps out ...you lose. ive seen chains saw completely thru the rail and topsides of a boat. Dont play stylish games with the stem head roller design..make it robust with the chain captivated in the fairleed with an oversize roller.

    Remember your anchor may be wedged into a rock. To free you pull up slack, motor on top of the fouled anchor then attempt to break free with the mass of the boat. Huge load on the stem head gear applied 90 Degrees to the chain roller assemblys designed function.
     
  6. Patrick BLOSSE
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    Patrick BLOSSE La Terre entière.

    Hi to you both,

    In fact, I am looking for a discussion about energy and shock calcutions of efforts due to heavy conditions, in extension to Alain FRAYSSE work presented.

    I am considering a grade 70 chain as the best availalbe product on the market at the moment. Do you think so ? Do you know any better product ?

    Kindly.

    Patrick
     
  7. michael pierzga
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    michael pierzga Senior Member

    Tough choice.

    . Galvanized chain reaches its working life when the galvanizing is worn away. Nearly impossible to have chain regalvanized at an affordable cost.

    As a result I use cheaper, commonly avaible , grade 40 Chain so that I can replace every few years with new chain.

    I did a quick internet search and couldnt find any source who has actually fitted a load cell to the ground tackle and recorded loads.

    Is ther such a load cell that can record peak loads while being part of the ground tackle ?

    This is a brief primer on ground tackle for people not familiar with the terminolgy

    http://www.rocna.com/kb/chain
     
  8. Stumble
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    Stumble Senior Member

    Patrick,

    G70 is pretty much the ideal, but there are some issues with it.

    1) it doesn't match many wind lasses so you need to confirm that it will work with your gear
    2) it is very expensive. The price can often encourage people to try and make do with less than ideal quantities of chain.

    Otherwise it is the strongest generally available chain, and because of its hardness is very resistant to abrasive damage. There are some concerns about the temprature hardening making it brittle, but the manufacturers don't indicate that G70 is any more susceptible to shock damage than any other chain.
     
  9. Milehog
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    Milehog Clever Quip

    I've read re-galvanizing G70 can be tricky because of the heat treatment if the chain.
    Possibly a vertical windlass with it's 180* degrees of chain wrap would give the gypsy more purchase on the hard chain.
     
  10. jonr
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    jonr Senior Member

    > Is there such a load cell that can record peak loads while being part of the ground tackle ?

    A S load cell of the right rating.

    You want a good amount of nylon line to serve as a shock absorber.
     
  11. michael pierzga
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    michael pierzga Senior Member

    I was thinking of a load cell that acts like an electric fuse. You install a 2 ton cell and when you exceed this the .,"Fuse " blows. Upon examination you would observe that last night the loading exceeded two tons

    Anything with electric cables would get destroyed or fouled.

    On many boats , particularly large ones or boats with nested anchors , snubbers are to difficult to use. I never use them
     
  12. Easy Rider
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    Easy Rider Senior Member

    The greatest anchoring variable is the sea bottom.

    Not equipment.
     
  13. Stumble
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    Stumble Senior Member

    Their are plenty of load cells that can go in an anchor system, but frankly I don't ink it is a good use of money. Taking the two grand or so and upgrade your anchor size, or length of chain is probably a better use of money than a load cell.

    The only place I really get the use of load cells is on boats that are incredibly rig tension dependent, like TP 52's, where getting the tension wrong by minuscule amounts can change the way the boat performs. Or for long distance racers, where a .01kn over two weeks may matter. For the average sailer I just think of them as expensive toys.
     
  14. ImaginaryNumber
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    ImaginaryNumber Imaginary Member

    Is there a reason why wire rope is not used for an anchor rode? I understand it is cheap, and lighter than chain for a given strength.
     

  15. michael pierzga
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    michael pierzga Senior Member

    Fishing trawlers use wire rope. The problem with wire is that you need a reel winch to handle and store the wire
     
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