So, two nations are in a war, land is off-topic as it's filled with zombies and necromancer zombies. The other logical option is the sea.
Now, one nation has these creatures, called wyverns.
Wyverns are quadrupedal creatures, capable of flight. They retained five digits on both their forelimbs, with an extra sixth one being modified into the rest of the wing, however, wyverns' posture is similar to that of a vampire bat, which makes fine-manipulation awkward. They're lightly-built and if were to stand on two legs, they would probably reach four meters (mostly because of their long necks). Wyverns have human intelligence and are capable of speech.
Now, they'd make for great scouts and messengers, however, for some reason, they also have to board enemy ships and fight.
The world's technology is roughly an age-of-sail level, except for that guy, but he stays in the background.
Now, wyvern flight is not so super. For a start, forget carrying stuff, as you wouldn't be able to take off even if the load was only a few kilos. And then there's the fact that it's not actually powered flight, just gliding for the most part.
Wyverns are people, and they hate throwing away their lives like a Survey Corps(e) member in Attack on Titan, so don't even think about screaming "Shinzou wo Sasageyo!" and charging into a suicide mission like Leeroy did.
So, I need to find a reasonable tactic/method for wyverns to board enemy ships, while knowing they can't take off with stuff. What could that tactic be?