Before you give up, it might be worth checking out that Adam MacNab 1804. You can get a photocopy of the actual page from the baptismal register in which the baptism was recorded from scotlandspeople.gov.uk and only from Scotlands People. It is a pay per view site but much cheaper than any other source of bmd records in the UK. Also, you can do a lot of searching and narrowing down on the site for free before you actually have to pay. You find the record you are after, buy 30 credits for 7 pounds and then use 6 of those credits (about £1.50) for the copy. It is instantaneously on your computer screen to print off, no hanging around for the post to arrive, and remains in your account permanently. You can get 5 records for your 7 pounds.
These pre-1855 OPRs are hit and miss. At worst you might only get the name of the child, father's name and date of baptism. At best you get parents, address, occupation, witnesses and anything else the registrar might think fit to add. Most are somewhere between the two. Got to be worth a look at the 1804 Adam MacNab in case it gives a father's occupation of "sea captain" which, while not definite, would certainly look very promising.