Vasa (ship) - Causes of Sinking

Causes of Sinking

In the 17th century, the design requirements and calculations for building a ship existed only in the head of the shipwright. Scientific theories on vessel design or stability had not yet been developed, so important factors like the ship's center of gravity had to be estimated from the builder's experience. The hull of Vasa was divided into three decks and a bottom compartment containing the ballast, which consisted of large, tightly packed stones. Upon salvaging, the ship was found to have an intact hold full of ballast stones. Vasa carried 120 tonnes of ballast, but this was not enough to counter its considerable weight above the water line; even a light squall would have seriously destabilized the ship. Common practice of the time dictated that heavy guns were to be placed on the lower gun deck to decrease the weight on the upper gun deck and improve stability. The armament plans were changed many times during the build either to place 24-pounders on the lower deck along with lighter 12-pounders on the upper deck or to place 24-pounders on both decks. The gun ports on the upper deck were in fact the correct size for 12-pounders, but in the end the ship was finished with the heavy 24-pounders on both decks, and this may have contributed to poor stability.

Warships of the period, even when properly armed, were highly unstable. A major reason for this was that they were built with high aftercastles to provide a platform for soldiers to fire upon the enemy with small arms. Also, Vasa may have had the additional problem of an upper hull built with thick wale planks that were much too heavy. This might have occurred because of inexperience with two-decker ships or because of the possibility of adding even heavier armaments in the future. However, nothing is inherently wrong with the hull form of the ship; it is within the norms of the period. Later designs, for example English ships of equivalent firepower developed after Vasa, used their heaviest guns on the lower decks and lighter ones on any upper decks, where extra weight was most likely to be detrimental to stability and the righting moment of the ship. Inwardly curved topsides, so-called tumblehome, were also more pronounced on later designs, so as to bring the mass of the guns closer to the center line of the ship, thus increasing stability.

Captain Söfring Hansson sailed the new ship with open gun ports, which was uncommon. Usually, a brand new ship sailed first with closed gun ports to give the captain and crew an idea of how it would handle, as each ship built in the 17th century handled a little differently from every other ship. This decision allowed water entry through the gun ports when they dipped below the waterline, and the weight of the water caused the boat to stop righting and capsize. Finally, Vasa was supposed to head for Älvsnabben, the naval station in the outer archipelago, to take on all of its stores and personnel, and that might have provided more stability.