Not quite as simple as that. Mooring, within limits, is an ancillary use of the canal - and whether it is residential (fixed or moving) or leisure use is not entirely decisive. Once beyond the reasonable limits, it is no longer an ancillary use and/or you may have created a fresh planning unit such that it is no longer part of the main canal.
The rather vague, reasonable limits of ancillary use are more readily breached by fixed location, full-time residential use. But it doesn't change the principle. For example (and without case law!) An employee keeping an essential eye on water levels or whatever, but living in a fixed location might well be an ancillary use of the canal - and not require separate planning permission. On the the other hand, if you jam-packed a mile of canal arm with leisure boats such that no-one could reasonably leave to use the canal for cruising, you may have over-stepped the mark.