Why no single invention defines shipbuilding before 1800

What was the most important development in shipbuilding before 1800?

Cross-bracing is the initial choice, followed by the keel and iron nails. The broad time span makes a short list more appropriate.

Cross-bracing is the first proposed answer, but the unrestricted period before 1800 makes the choice difficult. The keel is another candidate because the question reaches far back into shipbuilding history. A suggestion of iron rivets is revised to iron nails during the exchange. The conclusion favours a short list of developments rather than a single invention covering the entire period.