I just finished this one last night, squeaking by with a bronze in the very last month.
It is a tough one with no captives coming in. My strategy was to build the black market and supply cutlasses only for the first frigate only. I used the schooner for raiding and kidnapping only at this point.
My first cruise with the frigate was amazingly successful, with $10,800 gold, 22 wealthy, 1 skilled and 10 recruits! The next two were similar, but on the fourth, she sank.
I was getting low on money and captives at this point, so I tried a cruise with the schooner and she immediately sank too. Luckily I did have a shipyard, but only one shipwright in process of building another frigate so it took a long time to get going. My advice is to kidnap 3 right away so you can build faster.
I went through several brigs and built another snow just for raiding but did send it on one cruise near the end and it was very successful too. In the last few months, in desperation, I set all my ships to miserly and got lucky with three good cruises and lots of wealthy captives, so ransoming them put me over the top with a hoard of 11,717 and score of 22,676.
So the bottom line is to keep cruising and raiding and be sure to have a good ship or boatyard building ships constantly. You will need at least a couple of good sawmills going to do this too. It's a matter of luck and brute force as Charlemagne says.