The Bowditch

Bowdich 1st Editon

"The New American Practical Navigator" 

Most of us call this incredible encyclopedic text simply the Bowditch.

Everyone who has ever studied boating navigation has used resources from this text, especially the tables. 

Nathaniel Bowditch

Nathaniel Bowditch, (March 26, 1773 – March 16, 1838) was an early American mathematician remembered for his work on ocean navigation.

Nataniel Bowditch is often credited as the founder of modern maritime navigation.  His book  "The New American Practical Navigator" first published in 1802  and continuously updated ever since, is still carried on board every commissioned US Naval vessel. 

If you don't have a copy of the book yourself you can read it online, as it  is now in the public domain:

The New American Practical Navigator


Table #12 Distance of the Horizon

One of my favorite tables from the Bowdich is  #12,  When I ask my students how far away the horizon is when they look out from the seashore I get all kinds of answers, almost all way further that it really is.  

If your eyes are 5' above your feet you can only see 3 miles!  The earth is round and you can't see around a corner! 

If you need your radar to see 12 miles its antenna would need to be at least 40' above the water line.  Now of course, if your antenna is 12' above the water line it can see about 4.5 miles to the horizion and if your are looking at a big ship that is 50' from the sea surface to the deck, you might see it as it would be sticking up beyond your horizion adding about 9.5 miles to the visable range of your radar.  A smaller ship over the horizon will not show up no mater how powerful your radar is.  

Have fun with this table.