You need to check in. I understand that. Your choices are Great Harbor or Sopers. Got that part, too.

There is this " thing" on your boat called a VHF radio. You can use it to find out " what your chances are" of getting a mooring in Great Harbor.
Start on Ch 16.

" Blind Squirrel, Blind Squirrel calling for traffic report in Great Harbor Jost.".

May have to repeat that a couple of times.

" Blind Squirrel this is Pure Vida. Go to CH xx_

"Blind Squirrel on CH xx to Pure Vida"

"Pure Vida copies, what is your question"

"Pure Vida, we need to check in and need a mooring, are there any open?"

" Blind Squirrel, Pure Vida counts 3 open"

" Blind Squirrel thanks Pure Vida. "

Done.