Any conscientious navigator accepts that the need to maintain regular log book entries has not been compromised either by GPS or the chart plotter. Amongst other headings, any log carries columns for ‘log reading’ and ‘course steered’. Race boats might add ‘speed through the water’. These are still important, but two extra columns make sense today. COG (‘Course over ground’, or ‘track’) and SOG (‘Speed over ground’) can be read off the GPS and entered in seconds.
The log book provides data to work up an estimated position. If GPS packs up, the log may conk out as well, but it’s unlikely we’ll lose track of time, which has always linked speed to distance. Given that COG and SOG have remained reasonably steady they offer an excellent path to finding a new position.