A large ship, with three masts, lay becalmed on the water, with only one sail set; for not a breeze stiffed, and the sailorssatidle on deck or amongst the rigging.
"What you could measure is the productivity of assets that are left idle for a day - the ship that doesn't get built and so on, " Prof Mayhew adds, with the caveat that the British economy is far less dependent on building things like ships than it was half a century ago.