This is a gunport design used for ships in 1:40 or bigger. It uses the sideways hull as base, but it could be adapted in to other hull designs.
The parts
The tanned parts are making up the hull where the gunport is mounted. The gray is the parts that make up the moveable part.
Steps
As a gunport is essentially a hole in the side of a ship, I start by presuming that there already is a hull built and focus entirely on how the 3x3 gunport can be a part of this.
This is the most basic side of a ship. The plates make up the planking and the 1x8 brick (3008) make up the decks.
To start off remove part of the hull, thus making a gap in it.
As the gunport is attached by hinges there is a gap that needs to be filled. I usually use a variation of the 1x2 plate in combination with a 2x3 plate.
The hinged bit.
The great advantage of this design is that it works very well in the upper curvature of wooden warships