[Public-list] Anchors

[Gordon Laco]

Hi guys - 

I have to jump in...

While chain anchor cables are disliked in some areas for the damage they can
do to the bottom,  a properly set up one has significantly superior holding
to one that is all rope, or rope and chain, given the same anchor.

1) if the right size of chain is used, strength is not an issue.  5/16" BBB
is suitable for our boats.

2) scope...a given anchor will hold better on a short scope with chain than
without...with a long scope it will significantly better.  Chain performs
efficiently what a kellett does inefficiently ; that is absorb yanks and
surges on the tackle by diverting energy into lifting of the line.  Further,
the weight of the chain causes that much sought after catenary that ensures
that the anchor feels as near a horizontal as possible force.   Good
seamanship dictates the use of a nylon shock absorber at the boat end of the
tackle, this is easily fitted and takes only seconds to remove.

3) the angle of the 'pull' of the anchor line to the bottom has everything
to do with the anchor's holding power.  The best anchor in the world will
drag if the force transmitted to it by the anchor cable is significantly
above horizontal.  A poor anchor will still hold well if the pull on it is
near horizontal.

For our main anchor we have 180' of 5/16" BBB chain. On the end of that we
have 10' of 3/8" BBB chain.  In most situations the boat never pulls hard
enough on the chain to extend it along the bottom (after the anchor has been
set.)  Once in a gale we actually pulled it tight...that was such a
remarkable occurence that we logged it.

I guess everyone has their preferences....

Gord #426 Surprise






> At 10:07 PM 10/9/05 -0400, George Dinwiddie wrote:
>> [...]
>> Funny, there doesn't seem to be much discussion of scope, however.  This
>> week I anchored a 5 boat raft (3 A30s and 2 bigger boats) in Baby Owl Cove
>> on one of those Danforth knockoffs that came with so many of the
>> A30s.  Even with only 6 feet of chain on that anchor, I felt perfectly
>> secure with a 7 to 1 scope.[...]
> 
> George... I agree with you that chain is not  important. Chain is really
> only for avoiding chafe on the bottom near the anchor which very useful for
> a permanent mooring buoy (at my marina, motion has even catastrophically
> chafed thru several chains on the bottom in less than 1 season) but
> unimportant in an overnight anchoring. (1) It adds no strength to the
> system - a chain is only as strong as its weakest link, like the line or
> shackle anyway, (2) you lose the stretchiness of whatever length of line it
> substitutes for, thus not helping any for shock load, and (3) the
> "flattening" of the anchor for horizontal pull due to the chain weight is
> meaningless. After all, the anchor only pulls loose when it is tight (!)
> and by that time the chain is off the bottom anyway. Even without any
> catenary, the angle with the bottom is only about 8 degrees. If the chain
> helps with that, it's trivial; a degree or two, maybe?, and (4) look at the
> weight you save in hoisting or bow storage.
> 
> So, my (our?) conclusion is that a rope only rode, with a good scope is
> perfectly ok for anchoring, even in heavy weather. I expect others may
> disagree.
> 
> 
> Bob Kirk
> Isobar #181
> 
> 
> 
> 
> 
> 
> _______________________________________________
> These businesses support your Association:
> http://www.alberg30.org/store/A30supporters.html
> Please support them.
> _______________________________________________
> Public-list mailing list
> Public-list at alberg30.org
> http://alberg30.org/mailman/listinfo/public-list


 1128960138.0