A boat travels six nautical miles. Another boat travels at six knots. The numbers match, but the statements answer different questions: how far, and how fast. Keeping those questions separate makes sailing accounts much easier to follow.
Put a label beside the number
A nautical mile measures distance; a knot measures speed. NOAA explains the distinction: one knot is one nautical mile per hour, and one nautical mile is exactly 1.852 kilometres.
That means “six knots per hour” is not the usual way to describe a steady speed of six knots. The time component is already inside the unit. Write the full phrase once if the abbreviation feels unfamiliar.
Try a deliberately simple example
Imagine a classroom example in which a boat maintains a speed over the ground of five knots for two hours. Distance equals speed multiplied by time: 5 × 2 = 10 nautical miles. In kilometres, that is 10 × 1.852 = 18.52.
Now reverse the question. Ten nautical miles at a constant five knots takes two hours. The useful habit is to write the units at every step, rather than trusting a number that has lost its meaning.
Keep the example separate from a passage plan
This calculation assumes a constant speed over the ground and leaves out the practical complications of a journey. It is a unit exercise, not an arrival forecast or permission to attempt a route.
When you read a passage account, look for what the writer actually measured: speed through water, speed over the ground, elapsed time, or distance along a route. If the terms are missing, leave the ambiguity visible. Our introduction to tides and currents gives another useful pair of ideas to keep separate.