If you are interested in Navigation, emergency or otherwise, check out The American Practical Navigator. An epitome of Navigation originally by Nathaniel Bowditch.

This is the standard navigation manual for any serious student. It also covers weather forcasting, maps, and a host of other interesting topics. A must read for those interested in navigation, ship operation or ocean studies.

For Scott
From Ch 22, pg 340, the distance (D) to the visible horizon in nautical miles is
D = 1.17 times the square root of the height of the observers eye in feet.

This book is free, on the web. It is about 27 megs and I don't have the url anymore as I have it on my hard drive. Google should find it.