NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2013 Mar 11, 14:56 -0400
Hi Dave
Attached please find the Spectral Density of Buoy 44025 (Atlantic Ocean, South of Long Island's Fire Island Inlet.
It shows for various frequencies/periods, the power of the wave. This is, of course, correlated directly to size. That is, the greater the amplitude, the greater the power.
Now comes the interesting part. We can see three peaks, at or about 9, 12 and 14 seconds. The waves at 14 seconds are reported by the buoy as the "dominant wave" at 5.2 feet, by NDBC. Yet your vessel will respond to all of the energy shown, not just the 14 second variety. There will be constructive and destructive interference in the waves alone.
So my question is then, when are you at the "top of the wave"?
It is for this very reason that the ongoing dip study is being measured from land. It entirely removes this complexity from our problem. Yes, the waves still affect us, but in a much more manageable fashion.
Regards
Brad
In long waves (couple ship lengths) the heave transfer function goes to 1. (Heave amplitude = wave amplitude) At the same time, pitch transfer goes to wave slope. (You're horizontal on top of the wave.
If you can see more than one wave on the side of the ship, you're not there yet.
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