This discussion reminds me of the one I hear from some people about speeding tickets.
They say the road and their car was designed to handle a speed of (pick your speed), but the ticket was issued for less than that speed, and the road was wide open and it was a sunny, dry day at the time of their ticket.
Good luck using that excuse to get the ticket dismissed.
How do you think these many arguments are going to hold up if the MP stops you for having either too many people (by count) or too much weight in your boat if there is a capacity plate on your boat? Of course, I don't think the MP rides around with a scale to weigh all your passengers, but even so, don't over load your boat, especially if there is a capacity plate.