Usually the second officer is responsible for the navigation of the ship.
This includes but is not limited to :
Check the proper working of all bridge instruments before departure
Select all nautical charts necessary for the crossing
Draw courses on charts in consultation with the Master
Check if all mandatory (and not mandatory) literature (Lists of Lights, Admiralty Lists of Radio Signals, Pilot Books, Notices to Mariners, etc) is on board
Keep all charts and books well corrected and up to date
Keep his watch on the bridge (usually from 00.00 to 04.00 hours and from 12.00 to 16.00 hours
Usually the third officer is responsible for the safety equipment of the ship.
This includes but is not limited to :
Check if all fire fighting equipment is present and properly functioning
Check if all life-saving equipment (life-boats, life-rafts, their inventory) is present and in order
Check if all pyrotechnics are present and not outdated
Check if all signalling flags are present
Check if all emergency panels on the bridge (fire alert, watertight doors, etc.) are properly functioning
Keep his watch on the bridge (usually from 08.00 to 12.00 hours and from 20.00 to 24.00 hours
NOTES
As a rule, the third officer runs his watch for the Master.
On ships where there is no third officer, the master usually keeps watch from 08.00 to 12.00 hours and from 20.00 to 24.00 hours.
Pierre Deseck