Hello,Welcome to Just Answer and thanks for your question. Do you know about when he was born or where? By tracing him do you mean you are looking for his parents?
We can do only one thing per question. What one piece of information about him would you like to begin with?
Thank you. I will see if I can find that for you.
I've got the marriage certificate of William McKersie 1879 he was 28 and lived at 70 Ashbornham Grove, Greenwich.
Then that would be the first step, since it would provide names and ages of parents. Sometimes they include other information such as occupation of the father. Here is the information you will need to order it http://www.gro.gov.uk/gro/content/ if this is the same William.
Name: MUCKERSIE, William Henry
Registration district: Marylebone
Year of registration: 1850
Quarter of registration: Jul-Aug-Sep
Mother's maiden name: Not available before 1911 Q3
Volume no: 1
Page no: 221
There was no baptism information online that could confirm that his father as Robert.
I did not find a Robert McKersie on any census for England and there was no birth or marriage record for him, and no death record.
The fact remains that there is no birth, marriage, or death record for him online from anywhere in England. Since you had told me he was a mariner, I didn't expect to find him at home with his family. However, censuses were also done on the ships, and in the armed forces barracks all over the world on census day, but his name is XXXXX XXXXX them.
I'm sorry all my hours of work didn't provide anything you didn't already know. The enxct step would be to hire a genealogist who can look for paper records that have not been transcribed and put online. You can find reputable ones at www.apgen.org or www.progenealogists.com Expect to pay about $75 per hour whether they find anything or not. One pays a genealogist for their work, not for whether there are records or not. Do be aware though that Progenealgists charges a non-refundable $1900 upfront to undertake any project.