There were always two aspects to the people of Penti: their world in the Second Sphere and their empire in the Third. The former came first, including its single great ocean and tiny islands. I used that imagery a long time ago for a book that was never finished. The empire grew out of the maps and was developed in the first Platinum Mind book as well as the Karasor series. In fact, it was the brief visit by James Stone that inspired me to write more about their empire and the problems between the clans.
The style of the ships used by the Penti are based on models I made out of Lego when I was just eight. I liked the idea of catamarans with a bit of WWI dreadnoughts and WWII bombers thrown in. The Kyzyl Kum and the scout featured in Platinum Mind but the former wasn't really explored until I came to write The Karasor.
I've always enjoyed the imagery associated with vast and impossible ships, like the Death Star and the warships in Star Wars to the original Battleship Galactica, and wanted one of my own to play with...