I'm quoting myself here, but I just got my first naval victory. Finished in 1694, Conquistador, Large, Epic (with the pathetic normalized score of 590). I declared in May 1689 at 65% sentiment with 9 privateers (and a frigate from John Paul not the Pope). I had two admirals, and 1 privateer had 3 stars while 7 had 2 stars and 1 was a rookie. The REF had only 4 warships, plus 18/12/14 other units. I placed some caravels at sea adjacent to Isabella, mostly as bait. [There were only 3 sea tiles between Isabella and the border, so my plan was to attack the REF after the first landings.]
When the REF first showed up they only sent 3 MoW, two of which attacked caravels. Both caravels escaped! Yes, they were both down to 0.3, but one had taken an MoW down to 10.4. Twelve units landed.
I counterattacked, but I only had 4 privateers in range, along with the frigate. I sent in a 2-star which was sunk, but the frigate finished that one off. Sent in another 2-star and it was sunk, but the 3-star admiral finished it off. Sent in another 2-star and it was sunk, leaving the MoW at 8.4 or so. So on the first turn I traded 3 privateers for 2 MoW and damaged a third. Meanwhile on land my dragoons killed 12 units without losses.
On the next turn a miracle occurred: the third MoW attacked a caravel, and the caravel sunk the MoW (and had 2.4 points left!!)
A few turns later the remaining MoW showed up, landing 4 units. I attacked those, and the dragoons went 4 for 4. Then my second admiral attacked the MoW and sank it. Victory, with 28 REF land units stuck in Spain.
However, it looks my naval effort was almost unnecessary. My dragoons killed 16 units without loss, while the navy sank 4 and lost 3 (actually, the navy sank 3 and the merchant marine sank 1). All hail the mighty caravels, with three fighting Men-of-War without losing a ship!
[The key to this result was Simon Bolivar's bonus to combat strength, plus the late LB surge that minimized the size of the Royal Navy.]