While a lot of the ground work (both art-wise and as a part of world-building) was done for the series during the development of Book 1, I did manage to pull together a few concept sketches for A Prison of Flesh. This includes drawings for the boats and Corella's favorite figurehead.
"As they drew closer to the Cahimierha, the colorful illustrations that ornamented the ship became clearer. While the boat had no figurehead, its hull was decorated in various geometric patterns and shapes, colored in gold, green and red hues. At the front of the ship was painted a giant snake’s head, its eyes two blocks of gold, its teeth two rows of vertical ivory lines."
-- A Prison of Flesh, Ch. 5
Sketch - The Cahimierha
Mixed media on paper: water color, gouache, ink
Conceptually, except for slight personal touches, I see all three ships on the book's expedition looking fairly the same. For instance, the Aergaeu features the addition of Corella's figurehead (see below). The design is based on the three-masted hoeker/hooker.
"Mounted to the prow was a figurehead carved from wood and painted in bright tones with great care. It was of a topless female body that was part human, part fish, with a single swath of cloth wrapped lasciviously around her breasts."
-- Not Gods But Monsters, Ch. 27
Sketch - Figurehead of the Aergaeu
Color pencil/watercolor pencil and ink marker on paper
While this first shows up at the end of Book 1, it makes its return in Book 2.
"Mounted on the northern wall, behind the pulpit, was a mural composed entirely of 3cm square tiles that ran from the floor to the vaulted ceiling. The multihued creation was mostly colored patterns formed from the tiles. Laid out at head height in the center of the display was a single tetrad of images, encircling an imbued ore that appeared to be affixed to the wall."
-- A Prison of Flesh, Ch. 01
Concept - Byraelian Tiled Mural
Digital, vector-based illustration. Created in Adobe Illustrator
This was put together as a rough concept for the tiled murals. You can see at the center is the Voenth ore.