DANISH Ancestor - Help Please

[Anne Wilson]

I would like to trace the details of my GGrandfather who was born in Denmark abt 1840 but I have very little info to go on, so I'm at a loss as to where to start! If someone could give me a few tips & point me in the right direction, I'd be really grateful.
What I do have:
He signed his 1868 South Australian marriage cert. as John Nielson (although it was registered under the name NELSON) & his age was listed as 28, giving a birth year of approx. 1840. His father was listed as Charles on same cert.
His death cert in 1878 gives his age as 38, once again confirming an 1840 birth, but unfortunately no further details regarding place of birth is listed on those early certs.
His trade was a mariner & I believe he came to Australia in approx. 1865/66. The last I've picked up from two 1877 Adelaide Hospital records (IF it's the same John Nelson) which says he was born in Denmark & arrived in the colony aboard the Alexander/Alexandra (listed differently on both records).
Oral family history says he was one of six children & he was born in Denmark!
Because of the Danish naming system what should I be looking for in the Danish census'. Would John be Johann...would Charles be Carl?? or would he be Neil Neilson??
 I'm very confused so any help on how to track him in the census' would be wonderful
Annie

[jorose]

As John gives his surname as Nielson (Nielsen) and his father as Charles then the obvious option is:

Johan Carlsen (son of Carl Nielsen)
or
Johan Nielsen (son of Carl Nielsen)

Plenty of possible variant spellings, e.g. Carl could also be Karl

Unfortunately these names are not uncommon and you don't have any idea of the place in Denmark he came from, which makes things more difficult.

According to Australian newspapers (NLA beta site), there does seem to have been a ship Alexandra around the 1866 period, possibly sailing from England to Sydney and Melbourne at least, and there was also a ship Alexander, a Dutch ship which came in from Boston to Hobson's Bay in 1866.

[Anne Wilson]

Thanks for the naming hints jorose
I guess without a mother's name it's going to be difficult to pin him down in the census' but I'll give it a go.
Excuse my ignorance but is the NLA site the same as Mariners in Australian Waters?
Annie

[jorose]

No, I was referring to this site:
http://newspapers.nla.gov.au/ndp/del/home

Ship arrivals/departures etc are often listed in the newspapers of the times, along with names of captains and sometimes of passengers, but not usually of ordinary mariners unless they'd gotten in trouble!  It does make a good starting point to figure out what date/port you should be looking at.

Best to search exact phrase and put "ship" in front of the name. e.g. "ship Alexandra" filters out all the other Alexandras who were not ships.

[Anne Wilson]

Thanks once again
Just one more question please 
Are there any online sites where you can trace a particular ship and/or crew details...I vaguely remember having read once where if you knew the ship's name you could possibly track it's crew...where they had signed on/off etc. Not just a crew list but more detailed info on the individual?