New sailors frequently want to know which reference books should be in their onboard and in home libraries. While the internet is ripe with websites, blogs, and forums, not all of the information is reliable or accurate. Having access to a basic library that has been vetted by publishers provides a standard against which the other sources can be measured. The books cited here have stood the test of time. The authors are well known and respected in the field.
Boats have system, plumbing, electrical, propulsion, and electronic systems. For solid, technical information Nigel Calder's books can not be beat. Calder is a well respected sailor who approaches sailboat systems with the eye of an engineer. He writes for both professionals in the marine industry, often publishing articles in professional publications as well as the boating public. The Boat Owners Electrical and Mechanical Manual 4thEdition will serve you well as foundation. If your boat has a diesel, then add Marine Diesel Engines: Maintenance, Troubleshooting, and Repair.
Charlie Wing's Boatowner's Illustrated Electrical Handbook delves more deeply into AC and DC electrical systems. As you were told from childhood, electricity and water don't mix. DC wiring is different from AC wiring, and boat wiring is different from residential wiring. Keep your boat safe and follow Wing's guidance.
If your boat has a head or water tanks, then Peggie Hall's book, The New Get Rid of Boat Odors: A Boat Owner’s Guide to Marine Sanitation Systems and Other Sources of Aggravation and Odor is a must have. This book is invaluable when dealing with a chronic problem onboard, foul smells. The book is authoritative, informative, short, and reasonably priced.
Keeping the mast pointed skyward and keeping lines attached where they should be are major concerns for sailors. The definitive book on the subject is Brion Toss's The Complete Rigger's Apprentice: Tools and Techniques for Modern and Traditional Rigging, Second Edition. Whether you are want to understand the forces and dynamics of keeping a mast vertical or to simply splice and eye into three strand rope, Toss's book is the answer. While the book often deals with highly technical issues, he presents information in an easily read and understood manner. He knows his stuff and he helps the reader know it too.
That's it, five foundational books.