G
glennwaus@netspace.net.au
Fri, Apr 12, 2002 6:47 AM
Most modern lightweight anchors are designed to work with the pull on the
shank being no more than 8 degrees above the horizontal. This includes
Danforths, Fortresses, Ploughs, Deltas, and their variants. The sine of 8
degrees = .139. To achieve the required angle with an unweighted line,
line must be (DEPTH/.139) long or about 7.2 times the depth of the water.
This is where the famous 7:1 scope requirement comes from. Any weight
near the shank lowers this requirement. So a length of chain placed next
the shank of a lightweight anchor satisfies two requirements at once. It
lessens the slope of the line and protects the vulnerable nylon from
abrasion. Since the anchor rode is only as strong as its weakest link, the
chain should have at least the proof strength of the breaking strength of
line. This condition is usually satisfied by chain one size smaller than
....and he's right of course, except that I'm always worried about weights
passed down the rode to decrease the angle of incidence, because if the
wind/current is strong enough to straighten the rode, then you'd better have
all the scope you can muster.
Cheers
Glenn Williams
Port Phillip
Australia,
Larry said:
> Most modern lightweight anchors are designed to work with the pull on the
> shank being no more than 8 degrees above the horizontal. This includes
> Danforths, Fortresses, Ploughs, Deltas, and their variants. The sine of 8
> degrees = .139. To achieve the required angle with an unweighted line,
the
> line must be (DEPTH/.139) long or about 7.2 times the depth of the water.
> This is where the famous 7:1 scope requirement comes from. Any weight
placed
> near the shank lowers this requirement. So a length of chain placed next
to
> the shank of a lightweight anchor satisfies two requirements at once. It
> lessens the slope of the line and protects the vulnerable nylon from
> abrasion. Since the anchor rode is only as strong as its weakest link, the
> chain should have at least the proof strength of the breaking strength of
the
> line. This condition is usually satisfied by chain one size smaller than
the
> line size.
>
> Larry Z
....and he's right of course, except that I'm always worried about weights
passed down the rode to decrease the angle of incidence, because if the
wind/current is strong enough to straighten the rode, then you'd better have
all the scope you can muster.
Cheers
Glenn Williams
Port Phillip
Australia,
