Museum of Ancient Inventions: Keel Breaker

Keel Breaker, Sienna, 15th Century CE

A keel breaker is a counterweight hull-piercing device. It was originally designed by Mariano di Iacopo (or Jacopo) 1382-c.1453), known as Taccola. Like many men of the early 15th century, Taccola was an antiquarian and inventor. He viewed himself as an inventor, but also as a restorer of ancient knowledge. He was sometimes called the “Archimedes of Siena,” a title that refers to his ancient predecessor. The keel breaker was designed to rest underwater in shallow lagoons and marshes, especially around the ports of Talamone and Orbetello. It was intended for protection against pirates. When the trigger mechanism is tripped by the hull of a ship a counterweight is released downward and a claw extends upward piercing or tearing the keel (hull) of the ship.

Method of Construction

Constructed by: Stacey Cooney and Dara Weiner

Drawings by Taccola and others based on his work, served as our model. The support structure and arm were made of wood. The claw was either metal or wood. Its base was a tray in which stones were put so that it would remain on the bottom of the lagoon. The counterweight was also a tray of stones. We constructed our model from Taccola’s schematic. We chose to construct the entire machine from wood. Where Taccola might have used iron pins or have lashed the materials together with cords, we have used nails and wood glue. We used the ban saw, drill press, and sanders to shape the claw and cut the supports. We pondered whether there was anyway to reset the mechanism, but due to the lack of writing on the device, we can’t be sure if it could be reused. However, in light of the fact that once a hull is pierced the boat sinks, the sinking boat probably landed on the keel breaker, making the issue of resetting moot.


Galluzzi, Paolo. Mechanical marvels: invention in the age of Leonardo. Florence: Instituto e Museo di Storiea della Scienza, 1997.

Prager, Frank D. and Gustina Scaglia. Mariano Taccola and His Book Di Ingeis. Cambridge, MA: MIT Press, 1972.


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