Skakel, a nephew of Robert F. Kennedy's widow, Ethel Kennedy, says in the appeal filed late Monday that Michael Sherman had significant financial problems and did not devote enough money to prepare the case.
He says Sherman failed to challenge the state's star witnesses by finding witnesses who rejected his claim that Skakel confessed to the crime.
Skakel says Sherman also did a poor job in closing arguments.
Sherman says he did all he could to prevent Skakel's conviction.
Skakel is serving 20 years to life in prison for the fatal beating of Martha Moxley in Greenwich in 1975, when they were both 15.