Knomad...
Your interpretation is a little off... consult a lawyer or you can ask the MP. When I did (both) this was what I was told.
270-D:1 Definitions
VI. "Headway speed'' means 6 miles per hour or the slowest speed that a boat can be operated and maintain steerage way
The interpretation of the law is that you are allowed up to 6 MPH, if you are above 6 MPH you must be able to demonstrate that you need the extra speed to maintain steerage. (Spring current in the Weirs Channel for example)
The reasoning is that different boats need different speeds to maintain steerage, but it is essentially universally recognized that 6 MPH works in 99% of cases. Most people think that No Wake Speed = DEAD SLOW and it does not.
There is no such thing as no wake... any boat moving forward displacing water will create a wake of some sort. The height of the wake is certainly debatable.
Here is an easy explanation:
https://en.wikipedia.org/wiki/Wake
I apologize, but as an engineer, the term No Wake really bugs me as it is physically impossible for a boat.
Woodsy