There is several elements to this. It is public space that is being occupied, so in my view, there is a duty of care associated with that. The other aspect, is it is very difficult to put a price on fair compensation for having excuse use of a public space. I thought the cost covers AT's admin, not the compensation of the public amenity. Much the same as the water rights argument.
Rightly or wrongly, I think the duty of care extends to keeping the boat seaworthy and well maintained. As an example, our club requires that, and actively chases up any boat owners who are letting things go. It