# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Measuring (and Calculating) Dip
Date: 2013 Mar 19, 15:39 -0400

Frank

If it yields the exact same result as (h-h'); where h is height of eye and h' is 1/2 of the peak to trough wave height; then either both are bullshit or neither are bullshit.

And yield the same result they do.
Perhaps you can offer a case where they differ by a "significant" amount.  Significant being left to your perogative. Please don't offer the case where the height of eye is less than 1/2 the wave height, we can see that doesn't work for (h-h') either.  The table stops at zero.

Regards

On Mar 19, 2013 3:27 PM, "Frank Reed" <FrankReed@historicalatlas.com> wrote:

"The wave height correction is by atan((wvht/2)/(3860*sqrt(h))"

Oh my, oh my... Brad, this equation is bullshit. I should have been more blunt in my previous explanations. I really thought that if I spelled it out to you carefully and slowly, you would see the issues yourself without the need for blunt language. I guess not.

The correction for wave height is simple: your height of eye should be measured from the tops of the waves as nearly as possible. If you're on a vessel on open water, you can look over the side and see those wave tops. If you're at some protected location, either on shore or in a cove or some other protected waters, you should count your height of eye from your best estimate of the wave tops at the horizon. NO OTHER CALCULATION IS REQUIRED.

Here we see another problem with mathematics in celestial navigation. Sometimes folks get hooked on the "appearance" of accuracy and mathematical sophistication that comes with a "complicated" equation when the real solution is both "seat of the pants" practical and mathematically elegant.

-FER

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