Yet, if you wanted to use such a weapon, one of the problems being that ships are slow, and bigger shipa require a higher rank (usually a ship that even has obsidian shouls be a manowar+). Also, a ship requires mainly two things: wood/whatever material you are using, and wool. Obsidian is considered as armour, and the wood and wool need a percentage of the ship, or else the ship will sink. In conclusion, be careful about how much obsidian you are using, for power should not be abused!                      .