can anyone tell me about it? is it a very good book?
If you're talking about the book by the British Admiralty of that name... it is a standard reference that has been used for many years... I wouldn't say it is a good book, in that it is basically used as a reference and that's like asking whether the Encyclopedia Britannica is a good book... If you want a book on ocean passages and planning, I'd recommend Jimmy Cornell's World Cruising Routes instead, which has a focus on what small boat sailors are more likely to do, rather than the more commercial/military focus of the British Admiralty books.
The BA's Ocean Passages used to have a section on routeing for low-powered and sailing vessels, which for many years (decades? centuries?) was the bible for sailing ships. In the more recent editions this section was discontinued. This led Jimmy Cornell to essentially fill the void with his World Cruising Routes book, which updated the material specifically for yacht-size boats.
The Cornell book can certainly be recommended. If you find an older Ocean Passages it's a fascinating bit of sailing history and a great reference, but I think I'd keep it safe in my house rather than on the boat!
Thanks I have Jimmy Cornell book I was just currious of this one if it was a little better, somewhere I read it had some good charts in it