This book is a reprint of a genuine admiralty pocketbook for the average seaman. It seems to be a very faithful reproduction, the hardcover binding is excellent, and the size is very convenient.
It was written to explain the most important aspects of seamanship to a total novice, a book he could tuck into his pocket and refer to if he was uncertain about something. There are no arcane terms or information that you can't find anywhere else, but it does contain all the non-specialist knowledge a seaman would need.
I personally find it very useful as a reference handbook, if there is some term or idea I'm not sure about I can check the index or the chapter list and I'm sure to find it.