Hi Stan,
I fish a lot on the Antrim Coast and I have heard a few guys talking about Belfast Harbour being a good spot.
The opposite side of the river from the Odyssey can attract hassle from security guards based at the various offices but I think you'll be safe on the other side.
There are no permits required as far as I know.
You might get some grief from the drunks coming out of the Odyssey but I

do know that if you move downstream 100 yards to the old H&W site, there would be no distractions there.
Good luck