Frigates do require Iron -- it was mentioned in Greg's Strategic Resources article.
That's super weird.
One Frigate had as many cannon on board as a whole army. At the Battle of Blenheim, one of the major late Renaissance battles in Europe, the English-Dutch army had 66 cannon and 52,000 men, the other side, an alliance between France and Bavaria, had 90 cannon and 56,000 men. In the same war (the War of the Spanish Succession), there was a minor battle when the English tried to capture the island of Tenerife with a force of 13 ships with 800 cannon.