What should you include in a ship’s log?

05 November 2019

All boats are required to maintain a proper log when at sea. There are good reasons for this requirement above and beyond remarks made about the skipper’s non-existent tea-making abilities.  A properly maintained log allows a skipper to constantly evaluate current and future weather and sea conditions, monitor the vessel’s systems and resources (including her crew) and serves a critical purpose as an aid to navigation. 

A log can be kept in various ways and there are very many publishers producing a variety of different log books for the leisure sailor. However, there is some basic information that should be included in all log books.

They are;

  • Date
  • Names of vessel, MMSI Number & Call Sign
  • Number of persons on board
  • Time of each log entry (this may be local time, ship’s time or UT - and should be specific clearly)
  • Departure Port / Destination Port & associated HW & LW times and heights
  • Water Log (the ‘milometer’)
  • Water Speed (log speed)
  • Heading (True, Magnetic or Compass). Specify which are being recorded
  • Leeway (this can be estimated and should be recorded periodically in the log)
  • Position Fix (from visual fixes, buoyage or GPS)
  • Current Sail Plan
  • True Wind Speed & Direction
  • Apparent Wind Speed & Direction
  • Visibility
  • Sea State
  • Cloud Cover (Usually marked as a fraction of 8 - for example 5 / 8)
  • Barometric Pressure
  • Weather Forecasts
  • Battery Charge
  • Fuel Tanks
  • Bilge Check
  • Water Tanks
  • Comments (i.e. 4 Miles due South of Portland Bill. 3 more hours favourable tide. Port Watch on deck. Next W/C at 0200 hrs UT. All good.)

With this information faithfully recorded every hour, on the hour, the skipper can go to sleep safe in the knowledge that any changes in course, speed or weather conditions are being properly recorded. She might then leave instructions for the crew to wake her if certain things happen or if vessels are sighted. For example, “Wake me if wind increases by more than 4 knots, cloud cover increases to 6/8, wind changes direction by more than 15 degrees, visibility reduces below 2 miles or you see a vessel within 5 miles.  Wake me if you are unsure.”

If on a longer passage, it’s important to keep a record of when water tanks are changed or refilled, how many hours the engine / generator and battery charger / watermaker have been running, etc. Setting alarms for specific ocean weather reports is likely to become habitual as is periodic contact with home via satcoms. Separate logs are usually kept for vessel defects / repairs and crew health.

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