The Jargon File (version 4.4.7, 29 Dec 2003):

boat anchor
 n.

    [common; from ham radio]

    1. Like doorstop but more severe; implies that the offending hardware is
    irreversibly dead or useless. ?That was a working motherboard once. One
    lightning strike later, instant boat anchor!?

    2. A person who just takes up space.

    3. Obsolete but still working hardware, especially when used of an old,
    bulky, quirky system; originally a term of annoyance, but became more and
    more affectionate as the hardware became more and more obsolete.

    Auctioneers use this term for a large, undesirable object such as a washing
    machine; actual boating enthusiasts, however, use ?mooring anchor? for
    frustrating (not actually useless) equipment.


The Free On-line Dictionary of Computing (30 December 2018):

boat anchor

   1. Like doorstop but more severe; implies that the offending
   hardware is irreversibly dead or useless.  "That was a working
   motherboard once.  One lightning strike later, instant boat
   anchor!"

   2. A person who just takes up space.

   3. Obsolete but still working hardware, especially when used
   of an old S100-bus hobbyist system; originally a term of
   annoyance, but became more and more affectionate as the
   hardware became more and more obsolete.

   [Jargon File]