Hi David
Welcome to Rootschat.
Probably no help to you, but my Great Grandmother was a Christopher from Dorset. I've traced her line, mainly using Ancestry UK and Find My Past back to 1752. I've also visited the Dorchester Records Office which you can contact and for a fee they will research specific areas for you. By the way, each county in the UK has it's own archive records office.
The records office for Dorset is:
https://www.dorsetforyou.gov.uk/article/386613/Dorset-History-CentreThe one for Somerset is:
http://www.swheritage.org.uk/somerset-archivesI also found the Dorset Online Parish Records site very helpful which is free to use:
http://www.opcdorset.orgThere is a similar free site for Somerset records.
You can try here as well:
http://www.dustydocs.com.au/county/33/somerset.html?country_id=1I would not discount the Family Search site as a great deal of the records used by Ancestry have been acquired from Family Search and other free sites like FreeBMD.
There are a considerable amount of records transcribed for Dorset and Somerset that are available for free, but probably the first thing to do is obviously check that the records (i.e. passenger lists) actually exist. The UK National Archives website tells you what is available and where the records are located (some records are at the National Archives itself located in Kew (not too far from London), others are kept at the individual county records offices as mentioned above, and other various locations around the country such as the British Library.
Again, if the records are not digitally available, you can pay for an archivist to research for you.
This is the link to the National Archives Maritime archives:
http://www.nationalarchives.gov.uk/help-with-your-research/research-guides/crew-lists-agreements-log-books-merchant-ships-1747-1860/and from the same site, this shows you where other records are held i.e. Liverpool Records Office (most ships sailed to and from Liverpool).
http://www.nationalarchives.gov.uk/help-with-your-research/research-guides/maritime-history-records-held-by-other-archives/Some shipping companies (e.g. P&O), have their own archives as well that you could try.
Also, don't forget to post any queries on the specific County discussion boards on Rootschat. Many people will go out of their way to help you and even visit the records office for you. You will find Rootschat members very knowledgeable and very willing to help.
Anyway, I'm in Brisbane, Australia but have managed to get quite an extensive list of Christophers (on both sides, I have two sets of Christopher cousins marrying, which caused no end of confusion!)
Let me know if I can help you in anyway. Happy searching.
Kind regards
Caroline