A boat was traveling at 5 knots. It speeds up gradually at a rate of 2
Knots per
Hour.


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A vessel's speed may be recorded at specific periods of time, but
nobody familiar with the movement of a boat that is effected by winds,
currents, etc would presume that the change had been, or even likely
would be, evenly graduated over
a period of time.

If you boat is making 5 knots at 0500 and 11 knots at 0800, that
doesn't mean that it sped up at a rate of 2 knots per hour. It is
entirely possible that the boat didn't speed up until 0759, when the
wind shifted.