Eight of the 15 surviving crew members from a South Korean ferry that capsized in April are appealing their convictions on charges of negligence in the country's worst maritime disaster in more than four decades.

The eight, who have been given prison sentences ranging from five to 30 years, filed appeal papers on Thursday.

Video footage of the crew escaping the listing vessel after telling passengers to stay inside has sparked nationwide anger. The families of the victims, many of whom were high school students, have demanded harsh penalties.

The captain was sentenced to 36 years in jail on Tuesday, but was acquitted of homicide. Prosecutors had sought the death penalty. He is not among the eight who filed for appeal.

While a court ruled that the captain and crew did not do enough to help direct the passengers to safety, it said they were not the only ones responsible for the tragedy and the captain's negligence did not amount to an intent to kill.

A prosecutor involved in the case said after the rulings that the results are "disappointing".

The overloaded Sewol capsized while making a turn on a routine voyage to Jeju, a holiday island. The vessel was later found to be defective, and modifications that were made to increase passenger capacity made it top-heavy and unstable.

Only 172 of the ferry's 476 passengers and crew were rescued. Of the 304 confirmed dead or still listed as missing, 250 were students from a single school.

Defense attorneys have said the crew panicked and were not adequately trained to evacuate passengers.