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Initially, all the wars were fought either by using small guns, when both the ships used to draw nearer to each other or by ramming or using infantry troops to board the ship. But with the passage of time the methods changed.
The usage of heavy canons started by the end of 1400 but it was similar to the ramming and boarding technique as the canons were placed at the main deck. But the things changed by early 1500s when ships with gun ports into the sides were put to use. The advantage of these ships was that many canons can be used simultaneously and this increased the gun power per stroke.
As several tiers of canon had to be mounted in the hull, the constructers had to provide the ships with heavy framing to support the guns and also to get protected from the enemy’s shots. Also, the hulls were needed to be made deeper to ensure lower guns remained clear off the waters. More and more investment started pouring in for building, operating and maintaining these specialized ships. For this, many constructers started putting in more and more time in research and also in developing methods for calculating the displacement and design of ships so that the canons had sufficient freeboard to operate.

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