I would think a sea-side city, of all the cities would need such a legislation due to the abundance of boats in their neighborhoods.

Perhaps this is not about sight as much as about proximity. I'm guessing parking, walking or driving next to a boat could be not as safe as compared to e.g. a parked car.

Are you suggesting that walking by a boat or rv is somehow dangerous?

I don’t know about RVs but American boats are famous for spontaneously attacking pedestrians with their flying jibs.

If the boat is not correctly secured on its trailer, uses an inappropriate trailer, lacks chocks on an incline, has dangling elements, etc - then sure.