How the Constantinople Blockade should work

[Marcelo88]

In the game there are separate forts and ports but not port cities like Constantinople was.
For the siege to start it must first be sea locked. Greek fire was what prevented Constantinople from falling many centuries before because it dominated the sea and was supplied from abroad.

The same would happen if, once in the hands of the Ottomans the Balkans are invaded by Hungary Poland or Austria, they could reach Istanbul but never capture it.
It could only be reconquered with the help of Spain and Venice (as it happened historically with the formation of the Holy League), or bomb it and assault.

 

[Vin55]

why though? If you break the walls with cannons you can march on in. After 1453 cannons became better not worse. So this would only make sense if there are no gunpowder weapons being developed. Which were so your point is invalid. The only thing it would make the siege faster which is already a mechanic. Constantinopel wasnt an island.
And dont forget a normal Ottoman builds up to 150 galleys or so because of the awesome buildings they build in every single coastal province. So how would Spain do anything with their heavy ships.

 

[Blk82]

Historically, the siege of Constantinople took slightly less than two months, far quicker than what happens in game. While Constantinople was nearly impossible to siege in the medieval era, siege cannons already existed for decades by the 1444 start date. The Theodosian walls were already outdated by the 1444 start date, as they were build centuries before cannons existed. The bonus to defense for Constantinople makes sense in CKII, not so much in the EUIV timeframe.