A nautical mile is roughly 2000 yards, which is 6000 feet. A yard is 3 feet, which is 36 inches. A metre is 39.37 inches. That's about it.
There's really no need to worry too much, as SH4 allows you to use metric if you so desire. All navies used nautical miles, and a knot of speed is one nautical mile per hour, so again all you have to do is think of each measurement as a "unit", and go from there.
