Only four soaps ever started as hour-long programs, all on NBC: Texas, Santa Barbara, Sunset Beach and Passions. All three were at or near the bottom of the daytime ratings throughout their respective runs, but only one never lasted longer than four years. (Santa Barbara ran for nine years and Passions ran for eight years, followed by an ninth that aired on what eventually became the now-defunct Audience Network after NBC dropped the show in 2007 to make room for the fourth hour of Today.) I'm not sure if Santa Barbara (1984–93) was ever dead last in the ratings at any point, given there was a lot of low-rated competition at various points during its run (Loving, Generations, Ryan's Hope, Capitol and, having spiraled into its nadir during its final years following its 1982 move from CBS to NBC, Search for Tomorrow).
The Aaron Spelling-produced Sunset Beach was technically the least successful of the three serials, only lasting for three years from January 1997 to December 1999. (Fun Fact: It was the only conventional daytime show to ever be featured on the overnight block once known as "NBC All Night".) Oddly, despite consistently having poor ratings throughout its run, NBC chose to give Sunset a few multi-month renewals toward the end of its run because it performed well among younger audiences. That decision to renew the show short-term in early 1999, along with NBC and Sony securing a deal to renew Days of Our Lives after settling disagreements during contract talks (including issues over same-day PPV rebroadcasts on DirecTV, with speculation that it somehow would end up being picked up by ABC should NBC drop it, despite a lack of room on ABC's daytime schedule at the time to allow for a fifth soap), contributed to Another World getting the axe.
Passions (1999–2008; until 2007 on NBC) had similar issues as Sunset Beach, finishing at of near the bottom of the ratings (and doing at least slightly worse in total viewers than the soap it replaced, Another World (which placed eighth in the ratings out of the eleven soaps on the air at the time of its cancellation, ahead of only Sunset and Port Charles), did during the last couple of years of its run); it didn't land in last place among the soaps until ABC canceled Port Charles in 2003, reducing the number of daytime serials from ten to nine. Like Sunset Beach, Passions stayed on NBC because of its performance among teenagers and women 18-34 (it typically placed first among both demographics).