I do this often. First, your VHF should always be set to Channel 16 when you're underway, in the event you overhear or need to make a Security, Pan Pan or Mayday call. If you don't know, learn the differences between them. Second, the 'conversational' channels are 68, 69, 71 and 72. So, here's how it goes.
Both boats' VHF's are set to channel 16.
I hail my friend...
(me) 'Escapade III calling Menemsha Blue. Come in, Menemsha Blue"
(my friend) This is Menemsha Blue. Go ahead, Escapade III"
(me) "Hi. Tom. Switch to 72"
(me, now on 72) "This is Escapade III. Are you there, Menemsha Blue?"
(my friend) "I'm here, John. Over"
Now, a SHORT conversation to say whatever you need to say. State your business and end the call. VHF channels are NOT the place to catch up on old times. Nothing more annoying then trying to tell someone they need to drop an anchor, or set their fenders to tie up on my port side, and trying to break through a bunch of chatter. You want to talk about what you did last night? That's what cell phones are for.
(me) 'Escapade III switching to Channel 16. Escapade out."
(my friend) "Menemsha Blue out."
Both boats switch back to Channel 16.
As for contacting a local marina, you need to look them up before you leave, and note which VHF channel they monitor. Their phone numbers, too. It's often easier to telephone.
My .02
