I don't see a problem with narrow boats , there are one or two around Beccles and they all seem to be very well controlled , unlike some of the huge fly-bridge monsters that would be more at home cruising the Med .
I haven't seen any comments on some of the Dutch barges that are seen quite often surely they are also steel and are very well behaved.
I'm also old enough to remember the coasters heading up to Norwich through Reedham in the sixties now they really were something to dodge.