If you just keep using it and don't stop moving then it doesn't give the weed much time to grow :-).
With our old RIB that lived in the marina year round, we'd only haul out once a year for scrub and maintenance, and that wasn't anti-fouled.
There are some "special" (presumably boating-priced) brushes and scrubbing devices to try and help with just this, e.g.:
https://www.yachtingmonthly.com/gear...g-system-66045 . We used to have one for the sailing yacht, but never found it that useful in terms of being able to generate enough pressure and being able to guide it around all the chines and edges, etc.
With our RIB, admittedly in the Summer, we'd just anchor in the shallows and scrub it off, or put it on the beach, although I can appreciate if you're talking about the current season that may not be highly desirable!
Failing the above, do you have or can you borrow a trailer to just haul it out and scrub off occasionally if you want to?