John Flavel (1630–1691) on 1 Peter 3:19–20

If you look into 1 Peter, 3:19, 20, you there find that Christ "went and preached unto the spirits in prison; which sometime were disobedient, when once the long-suffering of God waited in the days of Noah." The meaning of which is, that in the days before the flood, Christ by his Spirit strove with the disobedient and rebellious sinners in the ministry of Noah, who then were living men and women as we are, but now are "spirits in prison," that is, damned souls in hell, for their disobedience...

John Flavel, Christ Knocking at the Door of Sinners' Hearts; or, A Solemn Entreaty to Receive the Saviour and His Gospel in This the Day of Mercy (New York: American Tract Society, 1850), 97.

Bio:  
Wiki
DNB

Flavel's interpretation is right. The text is speaking about Christ in his pre-incarnate state in the days of Noah, and not of his intermediate state between his death and resurrection. I am weary of all the bizarre theories [one might even say 'myths'] that surround this text.

Flavel himself, however, may need some clarification. The "spirits in prison" are technically not in their final abode, i.e., "hell" in that sense, but they are in a place of torment among the unregenerate dead in their disembodied intermediate state, and awaiting their final judgment, i.e., "hell" in that sense. Flavel is not wrong in what he says, but the reader may be left confused because of the equivocations that can occur in the use of the term "hell."

For good exegetical studies on this, see the following commentaries:

Curtis Vaughn and Thomas D. Lea, 1, 2 Peter, Jude (Grand Rapids: Zondervan, 1988), 94–99. This is in the Bible Study Commentary series. I would highly recommend all the volumes by Dr. Curtis Vaughn in the New Testament portion of this series.

Wayne Grudem, 1 Peter (Grand Rapids: Eerdmans, 1989), 157–162; 203–239. This is in the Tyndale New Testament Commentaries series.

Paige Patterson, A Pilgrim Priesthood: An Exposition of First Peter (Nashville: Thomas Nelson, 1982), 134–146.