Star Trek, Hornblower, and the lone-ship voyage

How similar are the original Star Trek series and Hornblower?

They share the broad idea of an independently cruising ship, but the relationship is closer to homage than a close character or story parallel.

The main resemblance is the independently cruising ship and the camaraderie among its crew. Star Trek's five-year mission is associated with the idea of a ship sailing around Earth on its own, though the comparison is treated as an homage rather than a close parallel to Hornblower. A lone spacecraft also faces a different operating environment because space itself is continuously hostile to life. Submarine service provides an institutional analogy for operating crewed vessels where a failure of the surrounding life-support arrangements can be fatal.