Hi

Here's some things I would, you may or may not have tried these.

Look for a death record
Check immigration and passenger lists
Use variations of his name or wildcards in your search
Do a newspaper search, you will be surprised at what you may find
Was he living with parents, cousins, aunts etc
Look at his neighbours in the last census you can find him on and search for them in the following census, he could still be their neighbour but transcribed incorrectly.
Look on the national archives site for any merchant navy records, also check the wills.
Do a deep web name search. I use Pipl.com but there are many others.
Do a google name search remembering to put the name in inverted commas "Frederick William Strong"
Search as many free sites as you know, such as find a grave, billiongraves, Geni, My Heritage, Wikitree you may find someone doing the same research

These are a few pointers off the top of my head or of course there are many of us here willing to help.

Thanks, Tried all then census up to 1881. As he went to sea and by 1859 was an officer (Only Mate) in the merchant navy, I'm not surprised that he's not on a census list. I'll have a go at some of the other things you suggest.
Bryan