The members of the Ship-Clans consisted of those travelers that decided to remain on the great starships that had taken them across space to their new homeworlds. This group were reluctant to abandon the large vessels which gave them a great deal of power as they were the only form of space travel available to the Romulans at the time and allowed for constant contact between ch'Rihan and ch'Havran.
The Ruling Queen, T'Rehu, had the support of the Ship-Clans whose vessels allowed her to move her armies allowing her to conquer much of the planet. Later on, rival armies gained the Ship-Clans support through the use of crystals that allowed the creation of laser technology. However, ultimately, the time of the Ship-Clans came to an end when their vessels were too old to support and many of the ship systems were transfered to the developing colonies on the two worlds. This, combined with many departing Ship-Clan members, resulted in their end when the four ships made controlled crashes onto the new homeworld of the Romulan people. (TOS - Rihannsu novel: The Romulan Way)
Despite the loss of the Journey ships, the Ship-Clans remained a powerful force in the Romulan Star Empire's politics well into the 23rd century. In an attempt to break their hold on power, in the 2220s the Romulan Senate exiled them from the Romulan system to Imperial border planets such as Mirhassa and Ssuvat. The Ship-Clans countered by smuggling out with them valuable plants, such as those used to make tivish fabric, and used the proceeds from smuggling to fund the secret construction of a number of large starships with which they meant to leave the Empire entirely. In the event, these ships were instead pressed into service as heavy capital ships and troop transports for the Free Rihannsu during the Romulan Civil War in 2276, backing the installation of Commander-General Ael t'Rllaillieu, a kinswoman of Kaveth Ship-Clan, as Empress of the Romulan Star Empire. (TOS - Rihannsu novel: The Empty Chair)