Well, your log starts on tuesday - leaving the port - and you write down several times a day the important stuff like daytime, position, weather, heading, sightings, major events - and once a day distance sailed surfaced, distance sailed submerged, fuel state, torpedos left, ammunition left - plus important happenings aboard and thoughts of yourself considering your task.
And the next day you simply add one weekday as usual - wednesday in our case.
http://www.calendarlabs.com/online-c...939&m=0&v=year