Books Boxes and Boats "brings together a wide variety of websites and databases hopefully useful to anyone carrying out maritime related research but in particular librarians archivists and family historians. These include 'official' sites such as the National Archives and the Royal Naval Museum as well as websites run by enthusiasts," Some of the contents linked are:
Lloyds Register, with links to an incomplete sequence of 18th & 19th Century volumes scanned by Google and the 1930-1945 volumes from Southampton Library & Archive;
Lloyds List, with details of ship movements, marine casualties & maritime news, an incomplete collection from 1741 to 1826;
Mercantile Navy List. an annual publication containing "the most comprehensive listing of British vessels, incomplete starting in 1849;
and lots more.
Scattered in are resources explaining the records which you'll appreciate after you've struggled to interpret the many abbreviations used.
Thanks to Christine Jackson for the tip.