Stardock's Galactic Civilizations III Ship Designer Contest is pretty simple as these things go. It's open to everyone of legal age in their country of residence, with the exception of Stardock employees. Entries must be original, must not be "vulgar or harassing," (so that's the Good Ship Spacepeen ruled out), and have to be submitted by 11:59 pm EST on November 16. A panel of judges at Stardock will select the top eight entries, all of which will be included in the game; after that, fans will vote to select the best overall design from the eight finalists. The winner gets a $1000 prize.
Simple or not, I would urge any and all aspiring shipbuilders to check out the rules at the Galactic Civilizations III Ship Designer Contest page. More information and a really brief FAQ are up on the Stardock forums, and if inspiration is what you need, have a look at our Galactic Civilizations III Early Access review—bearing in mind that since it ran, Stardock has added the missing trade and diplomacy functions, which you can read about here.
Galactic Civilizations III is slated to come out in early 2015.