Too tall, too narrow, and the gunports open
The short answer has been known since 1628. The long answer is still being researched.
Vasa, the Swedish warship of 1628. Dates and figures come from the sources linked beside them; where sources disagree, we show each one.
The short answer
The museum’s short answer: Vasa was top-heavy, a little too tall and a little too narrow, with too little hull under water for what stood above it, and the gunports were open when a sudden gust made her heel. Vasa Museum FAQ
Top-heavy
The upperworks were too tall and heavy for the small amount of hull below the waterline. That might have made her fast, but it put the centre of gravity too high, so even a light breeze could heel her alarmingly. Vasa Museum
An appendix records the opinion of expert captains and shipwrights: the ship did not have enough ‘belly’ to carry its high, heavy upperworks. Vasa Museum
Hybertsson was an experienced, respected shipwright, but Vasa was new to him in size and armament, and there was no way to calculate a ship’s performance in advance: the mathematics was more than a century away. Vasa Museum
New warships were often unstable at first (‘tender’ or ‘crank’) and there were accepted fixes: change the guns, add planking at the waterline, or take off a deck. Vasa was so crank that she did not survive long enough to be fixed. Vasa Museum
The open gunports
Under the cliffs of Södermalm there was little wind. A small gust made her heel and slowly recover; at the gap in the cliffs at Tegelviken a stronger gust pushed her so far over that water poured in through the open lower gunports. Vasa Museum
The museum calls leaving the gunports open ‘a fateful decision’: closed, they would have kept the water out, and the ship might have survived long enough to be rebuilt. Vasa Museum
They knew she was tender
Before she sailed, captain Söfring Hansson had 30 men run back and forth across the deck while Vice Admiral Klas Fleming watched. The ship rolled so much that the test was stopped for fear she would capsize at the quay. Vasa Museum
Fleming was overheard to say ‘If only His Majesty were at home!’, but he did not report it, and the king was pressing for the ship to go to sea. Vasa Museum
What the inquest heard
Captain Söfring Hansson was imprisoned and questioned ‘before his clothes were even dry’. He swore the crew had been sober and the guns properly lashed. Vasa Museum
The ship’s master, Jöran Matsson, had stowed the ballast, 120 tons of stone, and said the ship was ballasted as deep as it should be. Vasa Museum
The builders said Vasa was built to Hybertsson’s design, which the king had approved. Hein Jakobsson added that he had widened the ship by around 40 centimetres. Vasa Museum
The 1969 article says no plans or models were used in building the ship, and the king had personally approved its main dimensions. USNI Proceedings, 1969
The museum calls the hearing, to a degree, ‘a piece of political theatre’: blame had to fall somewhere without embarrassing the king. Vasa Museum
In the end nobody was officially blamed or punished, and everyone questioned was eventually promoted. Vasa Museum
The modern research
Fred Hocker, an archaeologist at the Vasa Museum, measured every piece of wood in the ship and found it lopsided, more so than most ships of the time: there is more structure on the port side than the starboard. PRI, 2016
Hocker says that without ballast the ship would probably heel to port, the side she went over on. PRI, 2016
Hocker found the deck structure heavier than it needed to be for Vasa’s guns, probably because Hybertsson, who had never built a two-gundeck ship, erred on the side of caution. PRI, 2016
Some historians blamed the king for changing the ship’s dimensions after building began, but Hocker’s measurements found no evidence for that. PRI, 2016
In Hocker’s words, ‘the design was simply flawed from the beginning.’ PRI, 2016
The museum’s 2012 survey measured the whole ship digitally at more than 80,000 points, and found it leans more than had been thought. There were no drawings to build from. Vasa Museum, 2012
Two kinds of ruler
Four of the workmen’s rulers were found: two in Swedish feet of twelve inches and two in Amsterdam feet of eleven inches. PRI, 2016
Radio Sweden, citing the news agency TT, put a Dutch foot at 281 mm and a Swedish foot at 297 mm. Radio Sweden
A broken fragment of a rule, lost during building in 1626–1627, was found behind a hull plank removed in 2010. Both kinds of rule are found on Vasa, ‘but no two are the same length’. Vasa Museum
Radio Sweden reported that the researchers do not think the uneven shape made Vasa sink, though it could have made her slightly less stable; the gunports, for example, are not in matching places on the two sides. Radio Sweden
Our reading of the sources: no single mistake sank Vasa. A design that was new to its builder, with no way to calculate stability, gave a ship that was too tender; a failed test was not acted on; and the open lower gunports turned a heel into a sinking. The rulers make a good story, but the researchers themselves say they did not sink her.