Re: knots per hour
There is no term of "knots per hour", just simply knots. When speed was determined by a chip log which was just a float designed to not move through the water, the line attached to it had knots tied into it at set intervals. When the chip log was thrown over the stern of the vessel and stabilized in the water the line attached to it was allowed to run out of the spool that held it. At discrete intervals, a knot was tied to measure the distance. A timepiece, usually a sand dial was used to measure the time that the log was in the water spooling out the, line. The speed was measured in the amount of knots that went overboard. The math was knots per time thus already knots per hour and reported as knots.
I still use a chip log occasionally, and it is very accurate at low speeds.
Check out Chapman's Piloting. It has a section and pictures of the old chip log.
