Just throwing this out there...
If Charles Snr was a boilermaker then its possible he too was somehow connected with ships.

There are records of a Charles Sherlock / Shurlock, mariner, b 1848 in either Hyth, Beds according to the 1871 census (RG10; Piece: 3777; Folio: 125; Page: 8;) or Heath Oxford according to the following TNA record:
http://discovery.nationalarchives.gov.uk/details/r/C11738569In 1871 there is also an unmarried Mary Carter aged 30 from Liverpool lodging at Percy St Tynemouth. The family she is lodging with is also called Carter so may well have been family.
Possibly entirely unconnected but the 1881 census has the following in the Tynemouth Union Workhouse, North Shields:
Catherine Sherlock, 22, b Blyth
Mary Ann Sherlock, 3, b Bedlington
Isabella Sherlock, 1, b Blyth
I cant find Catherine in 1871 so whilst its a long-shot it may be worth getting the birth certificate of one of the children to see who their father was and whether he too was a boilermaker. If nothing else it MAY place Charles the mariner in North Shields at the right time