ssh, sftp, and public key authentication

[dave]

Hello,
    I've got a machine i use public keys on to which i'm trying to ssh. When
i created a key for this user i did not define a passphrase, yet i am being
asked for one when i ssh in to the box. I use the command ssh -i
<filename.pub> hostname however if i do sftp username at hostname i'm allowed
in no questions asked.
    Help needed!
Thanks.
Dave.