Re: Pier design and sand

N. Foldager


I have a 10" diameter, 50" tall steel pier. Empty, a solid kick to the
pier would produce 20 arc-second vibrations in the eyepiece that damped
in about 1 second. Filled with oiled sand, the amplitude dropped to
about 15 arc-seconds while the dampening time stayed the same. The
results were hardly scientific, but they were fairly well repeatable.
Of course Don is right, when he argues for as low mass as possible at
the top of the pier. That is also the part of the pier where I would
expect almost no bending to take place.

For that reason I would think that filling the pier *partly* might
give the best result: sand in the lower part where the bending is
maximal, but empty at the upper part to limit the mass at the top.

The results were enough on the plus side of the ledger that I left the
sand in, but I'd be hard pressed to say it makes much of a difference.
The most important is without question the dimensions of the pier;
lower and thicker is better (as long as the OTA can pass).

Best regards,

Niels Foldager

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