Rob, I agree with Gavin Bangor Marina gets the thumbs up. If you can manage it Strangford Lough is fab place to visit, its a fair run from Bangor, but well worth it. Folks could join you at Strangford if they don't fancy the trip by sea. Small wirlpools amazing, as are the big ones
as is the marine wild life centre on Portavogie side of the estuary. Seals plentiful near the enterance. But you must do the chart work prior to entering the lough as the "paddies" (thats shallow rocks are very close to the surface outside the channel). 2 large towers in the enterance give good navigation aids.
Lobster Resturant in Strangford recommended or fish and chips opposite and sit on the harbour wall watching the world go bye.