Old Sea Dogs Nautical Jargon Speed, Distance & Time Dead Reckoning – A method of estimating your position based on speed and course. Drift – The effect of current or wind pushing the vessel off its course. ETA – Estimated Time of Arrival. ETD – Estimated Time of Departure. Knot – One nautical mile per hour. Used instead of mph at sea. Log – A record of speed, distance, time, and voyage data.