# NavList:

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

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Re: Bowditch Table 15
From: Bill B
Date: 2005 Jan 24, 17:56 -0500

```Jim wrote:

> When I do drawings, the vertical angle that an observer would shoot between
> the top of an object over the horizon and the horizon has to increase for
> decreasing height of eye as the observer climbs down a 100' mast, but the
> table suggests that vertical angle increases (keep "Distance by Vertical
> Angle" constant, and change [H-h] appropriately as you look at Table 15).

Do not think you can keep anything but H constant.  This is more like
Rubik's cube, you can't change one thing without changing another ;-)

If I do keep "Distance by Vertical Angle" constant, tabular H-h increases,
as does the tabular corrected angle.  That we would expect, no surprises
there. Note however that the corrected angle includes a dip correction.  To
decrease H-h by say 5 ft (tabular angle 0.07, dif 45 to 0.08, dif 50)  I
must increase dip by 5 feet.  As the table includes negative corrected
angles, obviously dip exceeds the measure angle corrected for IC in a least
some cases.

As h is decreased, the angle would indeed increase.
As h is increased, the angle would indeed decrease.

As h is decreased, the absolute value of the dip correction would decrease.
As h is increased, the absolute value of the dip correction would increase.

As h is decreased, the difference between H and h would increase.
As h is increased, the difference between H and h would decrease.

i.e.  h has an inverse relationship to the angle measured, dip correction,
and H-h.

Imagine the situation where you can see the base/waterline.  The closer you
get to the object, the bigger the angle from waterline to top. An inverse
relationship.

Same here.  The closer you get to the object, the more of it you can see
above the horizon, so the bigger the angle.  Again an inverse relationship
but with a different equation where dip may be a big factor.

Any help there?

Bill

```
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