The 'F' maneuver cards should be used for maneuver & speed only.
Of most of the chase & capture/destroy the merchantmen games I've played, it seemed there was never enough turns to do much good before the quarry was off board.
I like the idea of trading guns for treasure, a true test to see how greedysome merchant owners can be. Use pennies or dollars, depending on your income for each cargo box. Your opponent keeps what they sink/capture, they pay for what gets through. (It's not the money, it adds a bit of realism to being a merchantman or a pirate/privateer)
A series of playtests would be needed to see how the rest would turn out.
If I ever get the time, between my other 'fun things' I'll try it out.

Keep up your good ideas.