What type of Baptism is mentioned in 1 Peter 3:21

Here is my understanding... 

1Pe 3:18-21  For Christ also died for sins once for all, the just for the unjust, so that He might bring us to God, having been put to death in the flesh, but made alive in the spirit;  (19)  in which also He went and made proclamation to the spirits now in prison,  (20)  who once were disobedient, when the patience of God kept waiting in the days of Noah, during the construction of the ark, in which a few, that is, eight persons, were brought safely through the water.  (21)  Corresponding to that, baptism now saves you--not the removal of dirt from the flesh, but an appeal to God for a good conscience--through the resurrection of Jesus Christ,

The NASB says 'corresponding to that, Baptism now saves you'. NKJV says 'There is also an antitype which now saves us--baptism'.

I don't believe Peter is speaking of water baptism for three reasons:

1. Water baptism itself doesn't save anyone

2. Peter makes the point that he is not speaking of outward ceremony or outward water/washing but that which cleanses the conscience through Jesus' resurrection.   

3. Water in his typology of the flood was the judgment of God, not the means of salvation. It was the water that killed those not in the place of safety. 

If we look at his analogy, God judged the world through water, through a great flood. The only means of salvation was being 'in the Ark'. That was the only safe place to make it through these waters of judgment. The Ark (picture of Christ) was that which saved them.

So what baptism is it that does save the believer today? It is the baptism that occurs when the believer places their faith in Christ and is placed 'in Christ' (which the Ark pictures). At salvation we are baptised into the death and resurrection of Jesus. We are then in the only safe place from the coming judgement of God. Verses that speak of this include:

1Co 12:13  For by one Spirit we were all baptized into one body--whether Jews or Greeks, whether slaves or free--and have all been made to drink into [40] one Spirit.

Rom 6:4  Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life.

Col 2:11-12  In Him you were also circumcised with the circumcision made without hands, by putting off the body of the sins [7] of the flesh, by the circumcision of Christ,  (12)  buried with Him in baptism, in which you also were raised with Him through faith in the working of God, who raised Him from the dead.

This is a spiritual reality the moment we are born again and it is this baptism and association with the death and resurrection of Jesus that saves us. We instantly are placed 'in Christ' (the Ark) at salvation and His history is our history. We are in the only safe place from the judgement of God. Water baptism is the outward expression of this reality. Water baptism acts out that which has already occurred at the point of salvation. Thus in water baptism we go down into the waters and rise up again, symbolising our association with the death and resurrection of Jesus. This is important, but again, it is not this act that saves us. It simply points to the spiritual reality that occurs at salvation. 

And all of this is only possible of course because Jesus was willing to take those judgmental waters for us as you pointed out. He experienced a baptism right unto death on the cross... for us!

Hope this helps. 

Iain.