Glenn Ashmore wrote:
It only take a few seconds of auditing to see how the spreadsheet works. It
is fairly simple. It is limited to 200' horizontal distance however so it
works fine up to about 220- 250' of rode depending on the depth. Beyond
that limit it starts dropping off chain and the result is invalid.

Yes, it appears that it functions better if the total rode is kept
under 200 feet. However, since the depth is initialized at 44 feet,
attempting to determine the trade off between scope and chain will
lead to wrong conclusions. The sheet is explicit in saying it works
up to 250 feet, this is clearly bogus.


While it is not some prime limit if you discount the point where the chain
lifts you really discount the need for chain or kellets.

Yes, I do discount it. And so do experts like Van Dorn and Hinz. My
issue is that the critical point is not when the angle goes above
zero, it is when the angle exceeds about 8 degrees. Modern anchors
are designed to keep digging in even when there's a small up angle.
As long as the scope is over 7 to 1, that angle is not exceeded.

This spreadsheet gives a biased view of the situation, implying that a
lot of nylon must be added to equal the holding power of a small
amount of chain. The example I used was: in 20 feet of water, 40' of
chain and 100' of nylon yields a horizontal tension of 254# to lift
the catenary, which is actually the load of a 35 to 40 foot boat in 15
knots of wind. The truth is the scope is already 7 to 1, and a well
set anchor will hold and probably continue to dig in and in fact
handle a much higher load.

Adding to this scenario, 20' of extra chain raises the tension to
400#; to do this with nylon takes over 50 extra feet. However, at
this point, the scope is almost 10 to 1, beyond what is normally
needed. Another approach is to replace the 100' of nylon with chain:
the all chain 7:1 rode yields a tension of 643#, implying that it has
150% better holding than the rope/chain rode, which is not true.

The prime benefit of the kellet comes when you need to anchor in short
scope, under 7 to 1, and weight is needed to keep the angle low.
However, by the sheet, even all chain at 5:1 is fully lifted at 228#,
and is even pulling at 12 degrees, which could unset the anchor. Even
adding a 20# kellet does not significantly raise the tension point,
although there is benefit in light loads.

Thus, the sheet can lead us to two faulty conclusions: First, that all
chain is vastly superior to a mix, and second that a kellet or heavier
chain allow you to use very short scope.

I'm not denying that the kellet can help in some situations, or that a
reasonable amount of chain is essential for secure anchoring. I'm
only claiming that its more important to understand what's really
going on.