Might as well start now - these things take time.
In Norway, we introduced the metric system in 1889, but there's still a lot of non-metric measurements still around, at least in common speak.
* Length of a boat are measured in feet.
* Lumber is measured in inches, two-by-four and so on.
* Most engines are measured in horsepower(though nowadays the kw/h is usually given as well).
* Firewood have different measures, most of them derived from the pre-metric system.
* distances at sea are measured in nautic miles
* Boat speed is measured in knots. (not sure what the status of these last 2 is regarding SI these days).
Knots are non-SI, since they're based on the non-SI nautical mile (1 knot = 1nm/hr). But they are a good example of why context is important; the nautical mile is absolutely superior to the kilometer for use in navigation (at sea or in the air). Forcing the SI unit there would actually make the relevant tasks more complex and more difficult.
It solves headaches that come from trying to project the not-flat earth onto flat charts.
As Wikipedia puts it:
"In most projections, scale varies with latitude, so on small scale maps, covering large areas and a wide range of latitudes, the linear scale must show the scale for the range of latitudes covered by the map."
"Mariners generally use the nautical mile, which, because a nautical mile is approximately equal to a minute of latitude, can be measured against the latitude scale at the sides of the chart."
so if we used gradians/gon where the full turn corresponds to 400 instead of 360, the kilometer would be an approximation as good as the (international) nautical mile.
* Length of a boat are measured in feet.
* Lumber is measured in inches, two-by-four and so on.
* Most engines are measured in horsepower(though nowadays the kw/h is usually given as well).
* Firewood have different measures, most of them derived from the pre-metric system.
* distances at sea are measured in nautic miles
* Boat speed is measured in knots. (not sure what the status of these last 2 is regarding SI these days).