Specifying drive to write IMG file to

Hi, I have installed Reallymine on my main Linux 320Mb HD. I have a defunct WD 2Tb HDD (dev/sdb) that I am trying to decrypt. I successfully started decrypting then realised that the IMG probably wont fit in the bin folder on my main 320Mb drive so I did CTRL C and checked out the IMG file. Sure enough it was finding photos and portions of MP3 files. Now I have added a blank 3Tb HD (dev/sdc) formatted in EXT4 to save the full IMG file to. However, now I cannot find the write command line to write to the new disk.
Tried sudo ./reallymine decrypt /dev/sdb /dev/sdc/decrypted.img but just got the error
"running decrypt: open /dev/sdc/decrypted.img: not a directory"
Tried variations of this but no luck. Where am I going wrong? Is it because Reallymine is not installed on the new disk?
Any help is really appreciated, especially if you're out there @themaddoctor