T&T: Anchor,chain,rope specs and use

Gary Bell tulgey at earthlink.net
Sun Apr 22 09:09:49 EDT 2007


The anchor rode thread is illuminating and the erudite listers are most 
impressive -- however I would submit that calculated aerodynamic forces 
on oversimplified and generally frictionless shape, at a fixed aspect 
angle, producing static tensil loading of a non-catenary anchor rode 
attached to an infinitely strong anchor securely wedged into the Rock of 
Gibralter only prevail on a blackboard (or in my case sketched on a 
soggy cocktail napkin).  Wind moving over water produces all sorts of 
waves to say nothing of other boats moving over nearby water producing 
wakes.   Wind speeds and directions vary almost constantly.   Currents 
tug on our boats, tides move us up and down, the boats squirm about in 
response to all these dynamic forces, and of course anchors find such a 
diversity of shapes and materials to slither through -- or over.  If one 
fitted a load cell to a real life anchor rode one would find that the 
dynamic peaks of loading are far greater than the average load (the sort 
of load these calculations might simulate). 

Ted G. has it almost right:

<snip>...There are
too many variables that cannot be well defined for this to be a problem with
an analytical solution. Just buy a big darn anchor!




I would amend Ted's comment by suggesting that an extra prudent 
(paranoid) anchorer should continue super-sizing the whole ground tackle 
system until the people on nearby boats start pointing and laughing, 
then go up at least one more size.   Note that this means every 
component of the system:  windlass/wildcat (and it's power system), 
stopper, rode (often nylon and chain), kellet/rode rider, snubbing 
systems, riding bridle, anchor, and all the shackles, splices and bolts 
holding the outfit together.  Better have adequate chocks and cleats, 
way too much chafing gear, a plenty strong foredeck, a deep and well 
drained chainlocker and a pocketfull of fresh lottery winnings.  The 
rest of us (I guess that would mean we less-than-perfectly-prudent or 
budget limited anchorers) will size our rode to the wildcat of our 
existing windlass, set out a couple of Ted's sized anchors (of different 
kinds to cover as many types of bottom as we can imagine) on the coolest 
anchor platform we can craft, deploy all the tricks and  gizmos  
mentioned on this list,  and still keep an anchor watch with the engine 
key handy.  Iffy business, anchoring.


Who would trust their life and property to the smallest anchor that 
would handle some expected condition?  We go for overkill!  The other 
part of the right answer here is mistrust.  Keep an anchor watch, best 
you can.  If not in person, at least with GPS, radar and/or fathometer 
alarms. 



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