Corky Scott wrote:

The folk etymology from deduced is not documented in the OED or any
other historical dictionary. Dead reckoning is navigation without
stellar observation. With stellar observation, you are "live", working
with the stars and the movement of the planet. With logs, compasses,
clocks, but no sky, you are working "dead".

Thanks for looking that up, Corky. Another explanation I've heard is
reckoning against something dead in the water (i.e. not under sail), but
that doesn't sound entirely convincing either. I wonder if it has any
relationship to the phrase "dead ahead".


All the best,


David