News f2s wrote:
....
Of course, the best way to reduce inertia stresses is to provide
lots of 'spring'.

On the matter of percentage of rope to chain in the rode, the
traditional story is that the catenary of a chain gives you
'spring'. It does, but only half what's available from a length of
nylon in most conditions.

The crude way to see this is to play with a bit of string. Put a 6
inch length of string on the table, pull its centre 1 inch of off
the straight line between the two ends, and measure the amount of
'spring' (assuming of course that chain alone will not stretch!).
Or do the maths. The answer is 0.3 inch spring. Give or take a
bit for curvature. That's 5%. Your nylon gives you 10% spring
without deformation, and depending on the weave, a further 10%
leaving you permanently stretched line (which you'd better scrap!)

Actually, I think you overstate the amount of "spring" a chain rode
provides. When there is still chain on the bottom, there is spring in
the system from lifting that chain, but when fully lifted into the
classic "catenary" shape, there is very little left. While the
deflection in the rode may look reassuring, it is the extension that
actually provides shock protection. For a typical situation
(according to Hinz) a 200 foot 3/8" chain will have only 2 feet of
extension left in winds as low as 15 knots. At 30 knots, it about a
few inches. In other words, if the boat tries to move aft, the chain
allows only 2-3 inches - the remaining movement will come from
dragging the anchor or tearing the deck fittings. Thus in a lull, or
between wave surges, the system may relax, but in the next gust or
wave the boat will be thrown back an then stopped short with virtually
no shock absorption.

Your system of 100 feet of nylon is prudent. I use 50 feet of chain
spliced to nylon, so in a blow I typically have 100 feet of stretchy
line out.