History - especially Romans - could be the perfect inspiration; at their time, there was no gunpowder.
From the image source :
The use of the corvus negated the superior Carthaginian naval expertise, and allowed the Romans to establish their naval superiority in the western Mediterranean.
The corvus is kind of a "boarding bridge", which allowed the Romans to use their experience in on-land warfare. You just need strong, and preferably well armored soldiers. Enemy archers or crossbowmen would stand almost no chance if your ground troops are as disciplined as the Romans.
Also, it's worth noting that they also had a ram and ballistas, proving the proposals made by other users very efficient.
However, there's a difference between pirates and romans : the latter ones are not interested in looting anything; they only care about defeating the enemy fleet.
You, on the other hand, only want to immobilize your enemies, but not to sink them, as in that case, all your loot would be lost. So a ram could be "too" dangerous.
This is actually the main advantage of the corvus.
Read more about the roman navy and their tactics on Wikipedia.