On 24Mar2017 0628, Timothy Collinson wrote:

> [3] I ask this because evidently my subconscious was remembering the
> (very very old) ship I spent two years on (which I'm pretty sure could
> NOT be started from the bridge!), got best fuel economy at something
> like 12 knots instead of the 20(?) I think it was capable of.

Aside from ships using nuclear power, just about all will be rather more
fuel-efficient at a lower speed than their maximum. Exactly what this is
will depend on their size, hull form, and power. For a non-planing hull
that isn't massively over-powered something around 1/4 of maximum power
will get you half maximum speed.

--
Rupert Boleyn <xxxxxx@gmail.com>
Chief Assistant to the Assistant Chief