Sane looked at the Crown Prince with confusion: "Iron hull? What do you intend to use it for?"
Joseph replied without hesitation: "Of course, it's for deflecting cannonballs."
Sane likewise shook his head with a smile, not hesitating: "That's impossible, Your Highness. Even to defend against cannon fire from a greater distance, say a 24-pounder at 500 meters, you'd need at least 5 centimeters of iron plating."
He quickly did the math in his head: "That would increase the weight of a fourth-level battleship by more than 250 tons. You know, even though steam battleships are quite powerful, such extra weight would reduce their speed to less than 9 knots, and would greatly affect the amount of coal and supplies they could carry."
He was being polite—in reality, for a fourth-level ship with just over 1,000 tons displacement, if external armor takes up a quarter of that, it's all but unseaworthy.
