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

[David&Joan]

Robin:

I use 9/16" nylon with 5/16" high tensile chain. This seems to work for two 
reasons:

1. I assume that the working load of the nylon is about 1/2 of its breaking 
strength. This gives you some margin for loss of cross section due to 
chafing. 1/2 of the breaking strength of 9/16" nylon approximately equals 
the 3,900 lb working load of the chain.

2. A rope/chain windlass for 5/16" HT chain works well with 9/16" nylon. 
Your 5/8" nylon would be a bit big for your 5/16" windlass.

Maybe the civil/structural engineers in the group can give you some rules of 
thumb for wind loads. But IMHO the wave surge effect is much greater than 
simple wind loads.

The holding power of your anchor is roughly proportional to the fluke area. 
That is why the Danforths do so well. But you need a big Danforth type 
(Fortress, etc) to equal 4000 lbs of holding power. I have a FX 37 Fortress 
that I would chain to the end of my 44 lb Delta for extreme conditions. This 
Fortress looks like it has 1-1/2 to 2 square feet of fluke area. Solid 
compacted soil has a bearing strength of  about 3,000 lbs per square feet. I 
doubt that even thick clay has that much bearing strength, maybe 1,500 lbs 
per square feet. So my big fortess can really hold about 2,000 to 3,000 lbs, 
much less than the working load of the 5/16" chain, and a lot less than the 
ultimate breaking strength. Fortress' web site quotes tests saying their FX 
37 can hold 2,000 in soft mud and 7,500 in sand.

YMMV

David

David