if your wanting to make a rapier style parrying dagger, the guard will be surround the hand alot more, have bigger curvy quillions( to trap the blade ) and have a short thick blade. This might look a bit out of place on a pirate so I would suggest a more simple style.

For example looking at sabre no. 398 above. Shorton the blade and stretch out the grip and hand guard.

Only my views though.