All starships other than Borg cubes and spheres leave massive unexplained holes inside the "envelope" defined by the extremities. A donut might be the best way to create a ring of sensors or shield emitters without adding unnecessary mass. But when you create a tiny ship, you probably would wish for everything you do build to be of standing height! Unless you think crew health is paramount, and a racetrack thus the best way for them to commute from their cabins to their action stations.
Timo Saloniemi
Timo Saloniemi