# NavList:

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

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Re: Was Bowditch Table 15, now confused
From: Bill B
Date: 2005 Jan 26, 04:06 -0500

```Jim

I have made some mistakes in my postings, perhaps violating the "Make it as
simple as possible, but no simpler" rule.

H-h should have read H-h/constant in my review of the formula, my reference
to the tabular value 10' minus 3.1 dip may have been in error in my
"impression" of the tabular value (T15) sans reading glasses; and as it was
calculated, not observed, how would dip really relate?  I don't know.  It
will require further thought.

My impression of mast (stick) height as a sailor varies from the actual
specs on length of the mast, to where it is stepped, and actually height
above waterline and/or deck.  As a side bar, I know big boat sailors that
will not come closer to shore (depth wise) than the height of their stick
from the waterline--plus a safety factor--in iffy weather; so if they do a
360 roll they do not stick the tip in the bottom.  When racing, they will
come closer/less depth to save the time of a tack (hence my desire to
evaluate loss of speed below hull speed due to depth and determine if it
nets out).  It may appear picky, but these are real-world concerns for
sailors I have the privilege to tip a pint (or two) with on occasion.

Perhaps like the strange concept (to me) of observing a 100 ft mast 5 nm
miles away from 70 ft above sea level and using T15, I too get tunnel vision
;-)

My *many* shortcomings glazed over, your site brings an interesting term,
until now sight unseen for me, into my vocabulary.  That being, "Sensible
Horizon."  Which I take to mean visible horizon. I can appreciate but not
calculate how that differs from the ? horizon (refraction(s) etc.)  Can you

Also in my sphere of ignorance, the term, "steered course."  It appeared in
the Silicone Sea problems Mike Burke was working through many months ago.
If the problem's definition was to be believed, it refers to course-over
ground after set and drift of current(s) and leeway etc. are taken into
account as "course steered.  I have a conceptual problem with that.  If I
steer 90d M and actually (given S.S. extreme examples) make 135d M over
ground, how can the "course steered" be 135d M?

Thanks

Bill

```
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