1. The Hero has greater speed and mobility. We've got the initiative in this fight, both because we're faster and because he doesn't want us to destroy his ship, which we've shown ourselves perfectly capable of and willing to do.
2. Ruin affects the ship, so we have authority over what is and isn't reliable footing.
3. We have some ranged options, be it the two discharged ballista bolts, broken debris from the ship, or the crewmen themselves. The last may be going a bit overboard though.
4. We can grab those grappling ropes, the curiously resilient bowstring, and had already grabbed that grappling hook. We can likely briefly restrict his motion or even turn this into a 3D fight if we break the floor, which would be even more in our favor.
5. Our most dangerous weapon - our tongue! Shut up, Gisena. We should try to find psychological weaknesses and strike at them. Not much to go on right now, but he's already engaged in banter, so we can take advantage of that to draw out more information.