The study of the development of stern rudders for ships is a subject studied internationally.
I shall give a brief summary. Clay models of boats with stern rudders are found in Egyptian Tombs of four thousand years ago. In the first century A.D. the Chinese were building big ships with stern rudders. At the same time in the Roman Empire some river boats and barges had stern rudders. However, the big ships on the grain run from Egypt to Rome had side-mounted steering oars.
The practice of putting stern rudders on big ships spread across the Indian Ocean. In the Islamic Middle East their big dhows had stern rudders by the start of the tenth century. The technology spread to the Vikings through Constantinople and up the Danube. Crusaders from north west Europe were so impressed with the dhows' performance - they knocked spots off the lumbering Christian transports - that they also took the technology back.
Representations of ships with stern rudders were carved into Tournai fonts - the one in Winchester Cathedral is dated 1180.
The Ipswich Ship Seal dating from the Hundred Years War?
If we look at the ship seal of Ipswich, round the outside the inscription in Latin translates as ‘The Master Seal of the Town of Ipswich'. There is an image of a ship with stern rudder and forecastles and a flag on the mast. This is a warship. Most ships of this time did not look like this, even those used for military purposes. There was no English Navy; if the King needed ships he summoned ordinary cargo vessels from the major ports.
At the beginning of the Hundred Years War (1337-1453), Edward III assembled a large fleet in the River Orwell comprising 370 vessels of assorted sizes. This was to transport the king's army and entourage, including horses, to Antwerp. They set sail on 16th July 1338 and had no trouble in getting there.
Again, in the summer of 1340 Edward assembled a fleet in the Orwell. However, the French fleet sailed up the Dutch coast and blocked the access to Antwerp. News got back to England and Edward had the fleet converted for a sea battle. At this time a sea battle was almost unheard of, certainly not on this scale.
About 180 ships had stern and forecastles and large crow's nests added. Only fighting personnel were embarked. This delayed departure somewhat but on June 22nd 1340, Edward boarded the Cog Thomas in the Orwell and led the fleet over to Sluys where the English captured or obliterated the entire French fleet: a stunning victory, the Trafalgar of its day.
To commemorate the battle Edward minted the Gold Noble coin which was first issued in 1344. The reverse has an image of the King aboard a warship, possibly a representation of the Cog Thomas. This design has a striking similarity to the Ipswich ship seal. So when you consider that the earliest accurately dated example of this seal is June 1349, I would suggest that this seal design was also produced in commemoration of Ipswich's part in the Sluys Expedition.