NavList:

Jackson,

A while back I wondered about an example in recent editions of Bowditch, and contacted HMNAO and USNONAO regarding it.  Apparently they agreed with me.  Question is whether the USNONAO will remember to do anything about it.

This is a summary of what went on, from the Celestial Tools Help:

The whole hour Moon "paradox":  Regarding v and d values and corrections, the Explanation section of the Nautical Almanac makes no procedural 

distinction between sights taken on the hour and those with minutes and/or seconds - if the body uses them, they should be applied.  For most bodies 

this does not matter, but in the case of the Moon, where the v and d values often exceed 5.9', resulting in v and d corrections of 0.1' (possibly 0.2' for 

a v or d value of 18.0'), this can create a "paradox".  If the non-zero correction is added to the hour value taken from the daily page, the Tot GHA will 

not be the same as the hour value, even though there are no minutes or seconds.  The 1995 and 2002 editions of the American Practical Navigator 

("Bowditch") do an example of a whole hour Moon reduction.  In that example, the v and d corrections are applied.  However, according to Catherine 

Hohenkerk of HM Nautical Almanac Office, although it is not clearly stated in the Explanation, when the hours and minutes are zero there is no need to 

go into the Increments and Corrections at all.  Sean Urban, Chief of the USNO Nautical Almanac Office, agrees with this, and is also of the opinion that 

using an example exactly on the hour was a poor choice.  Celestial Tools will not show increment values or v or d values or corrections for sights taken 

on the hour.

Stan

-----Original Message-----
From: Jackson McDonald <NoReply_McDonald@fer3.com>
To: slk1000 <slk1000---.com>
Sent: Thu, Nov 12, 2015 12:57 pm
Subject: [NavList] NGA to update Bowditch, seeks public input

The following press release could be of interest to many NavList members:

NGA to update Bowditch, seeks public input

By Carling Uhler, Office of Corporate Communications
9/28/2015

Nathaniel Bowditch’s “The American Practical Navigator,” often simply called “Bowditch” and regarded by mariners as the premier navigational reference, is due for an update, and the National Geospatial-Intelligence Agency wants input from mariners the world over. 

The first edition of “The American Practical Navigator” was a revision of “The New Practical Navigator,” the most popular navigational text of the 1700s. Bowditch, a famous mariner and mathematician, worked with other experts of that era to revise and update the original publication and published it in 1802. 

NGA and its predecessor organizations have been responsible for reviewing the publication and ensuring it meets the demands of the modern mariner since the 19th century. The U.S. government purchased the rights to the book in 1867 for $25,000. The U.S. Navy Hydrographic Office, an NGA predecessor, assumed responsibility for updating the publication in 1868, and it has been regularly updated ever since. Now in its ninth edition, the publication is freely available for downloadfrom NGA.

To keep pace with the rapidly changing world of navigation, each edition has included revisions to dated material, addition or deletion of new and antiquated methods, corrections to current publications, and further updates to maritime fundamentals, piloting, electronic navigation, electronic and celestial navigation, navigational mathematics, and navigational safety measures. Some past updates have included deleting obsolete LORAN information and adding bottom contour navigation and digital nautical charting techniques.

Collecting and publishing the most updated techniques, information, methods and data ensures “The American Practical Navigator” remains the reference resource for modern, practical marine navigation. "For the past two centuries, Bowditch has provided each new generation of sailors the theory and science behind the art of modern marine navigation,” said Gerard Clifford, NGA Maritime Safety Office. 

The deadline for users to insure their comments and feedback are considered for the new edition is June 30, 2016. The next edition of Bowditch is expected to be published and released by NGA in 2017. 

To submit contributions and feedback for the next edition of Bowditch, please visit the NGA Bowditch survey website, download the survey files, and send an email to Bowditch2017{at}nga.mil. Contributions may also be emailed directly toBowditch2017{at}nga.mil.

NATIONAL GEOSPATIAL-INTELLIGENCE AGENCY 7500 GEOINT Drive  Springfield, Virginia 22150 571-557-5400