"It's crazy how quickly you were able to retreive this information"
Not really - I've got years of practice and you gave really good information to start with. I started working on my own Norwegian ancestors and began haunting these messsage boards long ago checking for strangers who gave information I could try to find as PRACTICE for myself. There were far fewer online resources then but things have drastically improved and continue to get more comprehensive all the time.
Not being familiar with the Kristiansund areas I went to the NHDC census databases with my fingers crossed that John was actually born in 1865. I felt that Bjerkestrand would be the name of a farm or residence and that Petersen should be the "last name". I used database wildcard (%) to substitute for any spelling that might differ and used the 'Easy' version of the 1865 census because it allows a search which includes farm name for an individual.
I actually searched for (First name) Jo% (Surname) Pe% (Farm name) B%r%k%st%. Only one of the very limited returns appeared to be a match.
Tip - NEVER count on consistent spelling!
This is probably John leaving from the city/port of Kristiansund on or about 4 April 1888 -http://digitalarkivet.uib.no/cgi-win/webcens.exe?slag=visbas...