So for pirate round, I made a boat with only Vending Machines, Blue Barrels, and Money Stacks, I place 1 cannon, the whole ship sunk instantly, is the cannon weight to heavy?!
This is not a bug, locked, if you want to complain about balancing make a thread about it in the flood section in the future.
Cannons do have a lot of weight to them actually and you will need to balance your boat accordingly. The money stacks are good for counter balancing the cannon if used right.