In the 1620s, Sweden—at the time a regional power—had concluded its wars with Denmark and Russia, but was still at war with Poland. In 1625, King Gustav II Adolf signed a contract with the master shipwright Henrik Hybertsson to build four ships. The flagship Vasa was to be the most formidable warship in the Baltic.
However, on her maiden voyage in 1628 this magnificent ship capsized in Stockholm harbor. What went wrong? And whose fault was it? There was plenty of blame to go around, but political- and military expediency protected the guilty parties.
Although some of the cannons were recovered in the 1660s, it wasn’t until the late 1950s that salvage of the ship itself began. Today, the restored ship is the centerpiece of Vasamuseet in Stockholm. It has much to teach about history, naval architecture, project management, and human nature.
Naval warfare
At the time, naval warfare entailed capturing enemy ships. To that end, a warship carried as many soldiers as sailors. Warships had a single cannon deck with sufficient fire power to disable an enemy ship. Then the soldiers would board the ship and fight to take control of it. Of course losing a warship to one’s enemy would be a disaster, so Sweden’s Admiral of the Realm ordered sailors to blow up their ship if capture was imminent.
King Gustav was a fan of artillery, however, and Sweden made the best cannons of the day. After the Vasa’s keel was laid, he ordered additional cannons, necessitating a second gun deck to accommodate them. This change in the design followed the evolution in naval warfare tactics from capture to destruction of enemy ships. It took more firepower to sink a ship than simply to disable it.
The gun decks were inside the ship’s hull. Gun ports in the hull would be opened during battle and closed otherwise. However, the gun decks had to be well above the water line at all times to avoid taking on water. That is, these were cannons, not torpedoes.
Why did the Vasa capsize?
Ships float because they displace enough water to support their weight. The weight of the water they displace equals the buoyancy force. It acts through the centroid of the volume of the ship that’s below the waterline.
Ships remain upright because of the righting moment. So long as the center of gravity of the ship and everything on it is below the center of buoyancy, the righting moment will act to return it to the upright position. The farther below the center of buoyancy the center of gravity is, the greater the righting moment and the more stable the ship.
In the 17th century no one knew about centers of gravity and centers of buoyancy. But they had plenty of empirical knowledge about the stability of ships. They knew to add ballast in the ship’s hold to make it more stable. A stability test consisted of running back and forth on the deck between port and starboard to see how easily the ship righted itself.
Empirical knowledge works best when technology changes slowly. That way people’s intuition can evolve along with it. But when there’s a major shift in circumstances or technology, empirical knowledge can’t keep up. The second gun deck added a lot of weight above the waterline—well above the center of buoyancy. That is, the additional cannons raised the center of gravity above the center of buoyancy.
As the Vasa set out from Stockholm harbor, a light breeze caught the sails, causing the ship to roll. Unfortunately, it was so unstable that it capsized then and there. Most of those on board were able to swim to shore, but at least 30 of them drowned.
The inquest
One of the most interesting exhibits in Vasamuseet is the recreation of the Royal Council inquest that followed this fiasco. Most of the records remain intact, so there’s plenty of information to go on.
The captain supervising the construction of Vasa, Söfring Hansson, calls Vice Admiral Klas Fleming down to the ship…because he is worried. He has thirty men run back and forth across the deck and the ship rolls alarmingly. The Admiral has the demonstration stopped, afraid the ship will sink at the quay. Under pressure from the king to get the ship to sea, he orders Söfring to sail anyway. Months later, Vasa sets off on its first and last voyage.—Vasamuseet website
That is, they knew it was unstable, but no one wanted to tell the king.
At the inquest, expert testimony indicated that the ship lacked the hull depth and breadth to carry the heavy upper works. The builders insisted that they had followed the design the king had approved. They had even widened the hull to increase its stability.
The Royal Council faced a dilemma: whom to blame without either embarrassing the king or depriving the Swedish navy of the expertise it needed to continue the war against Poland?
In the end, no one was officially blamed or punished, and all of those questioned were eventually promoted. Hein Jacobsson [Henrik’s successor] worked at the navy yard until he retired in 1638, building a string of large, successful ships for the Swedish navy. Jöran Matsson [ship’s master] became a captain, and Söfring Hansson became the supervising officer for the navy yard. Klas Fleming was not even questioned, but went on to serve with distinction and died a hero’s death in 1644.—Vasamuseet website
Lessons for today’s engineers
In many ways this story is relatable for today’s engineers. My favorite projects have been for either of two kinds of clients: those who have no technical expertise but are willing to trust me, and those who know a lot and take a “hands on” approach. The most difficult clients are those who don’t know much but still want to manage every detail, especially if they keep changing their minds. King Gustav’s addition of the second gun deck after the keel had been laid made it hard to provide the necessary stability. This is why we have change orders—to document who orders what changes when, along with the estimated cost.
Implementing new technology always entails risk, as we can’t anticipate all the consequences. Factors of safety help to account for what we don’t fully know, but “unknown unknowns” can still trip us up. That’s why bench scale and pilot scale versions are a good idea, as are mockups. These trial versions help us spot potential problems and resolve them. By the time Admiral Fleming witnessed the stability tests of the Vasa, it was too late to remedy the problem.
Lastly, while expediency doesn’t always win over truth and transparency, that’s the way to bet.