Rafting is totally permitted/expected/at times required on most of our public docks. It's certainly considered courteous to ask permission if the owner's aboard, but in reality many of our public floats flat-out state rafting is to be expected.
We always fender outboard in expectation of possibly being rafted to while off on a shopping run.
No moorage fee discount for being three boats out either....
Here's the rafting we grew up with on BC's central coast!