This is the Wintertide which is a barge that I made up:
At first the ship had some problems. It was bending in the middle, putting minifigures in the command deck was tricky, and overall the ship looked a bit plain. To make the ship stronger I added 2×6 bricks under the deck and I added a removable roof on the command deck. The gun set the tone for the rest of the details like the foghorn, the smokestacks and the grill on the roof:
I used one of my favorite building techniques to attach the gun to the ship, five stacked plates on their sides are the same width as a 2x brick or plate.
There you have it. That’s how I built the Wintertide.