There are many great books in the public domain that can be found for free online as e-books. Amazon doesn't make it super straightforward to load them onto a Kindle e-reader though...
Where to find books
My first port of call is always Standard Ebooks. They are produced by volunteers and with very high quality standards (often better than what can be found on Amazon for old books in my experience). You can subscribe to their news feed (Atom/RSS) to be notified as new books get added. Nice.
The other classic place to go is Project Gutenberg, a library of over 75,000 ebooks. The quality varies, but quantity has a quality of its own of course.
But which specific books to get, I hear you say? The Riddle of the Sands and Two Years Before the Mast are both fantastic nautical literature.
How to get them on there
Many people recommend using Calibre software to manage your ebook collection and help convert and load it onto devices as required. Haven't tried it myself yet.
Amazon provides a send to Kindle service to convert and load documents onto your device by mailing them to your personal @kindle.com inbox. This also works for ebooks in the .epub format. The Kindle will use the file name as the book title, so keep that in mind. The advantage of this method is the books will still synchronise across devices. The downside is no cover art.
The alternative method is to connect the Kindle to your computer and transfer the file directly into the documents or ebooks folder. It needs to be in the .azw3 format. You can then also place a cover image into the system folder to make that show up. There are more complete instructions on the Standard Ebooks site. Since it's not "in the cloud", it won't synchronise across your devices unfortunately.
Written on 16 January 2025