Google is not helping me.  Am I inquiring properly?

Boothbay.

Definitely Dimillo's Floating Restaurant  

... With your prowess in cooking, there are many other excellent choices in the old port

No doubt!   But they don't sit on the water  😊

If you decide to shed your mermaid fins and head inland for a bit try Fore Street Restaurant.  One of my favorite haunts.

is that the restaurant  that you need to make reservations ions in advance?

I don't know about ions, but you should make reservations.  I've always gotten a table calling the same day or day before.  Have fun up in Portland. Great city.

.... Old port tavern, Gritty's, or the Irish pub (can't remember name) just before the ferry terminal-  
Maybe not right on the water, but close enough for me-  
Would love to just hang with you, eat and knock back a few Guiness!

If so it's pretty freaking close to the water  but  ewwwwww on the Guinness lol

Ri Ra is  Irish pub on water

I've heard good things

If you want good food in the Old Port, try Street & Co. and Fore St.  If you want to be on the water (and don't need great food) Flatbread (outside) or Dimillo's. If you want good food, on the water, go to Dockside Grill in Falmouth. It's 15 minutes form downtown.