Shells and Stones: Ballast and the Mary Rose

Ballast on a ship can be any type of material loaded into the hold that adds extra weight to ensure stability when sailing, counterbalancing the weight of the upper decks and sails. Without ballast, ships would become less stable in the water when the weight of cargo and stock is removed. Measurements and careful calculations are needed to ensure that a ship is balanced perfectly. In the Tudor period, ballast was solid, often made up of a collection of rocks and gravel, which needed to be manually carried through the ship to fill the hold.

Ballast found on the Mary Rose was estimated to weigh around 100 tonnes and included rocks and gravel, but also shells of cockles, oysters and periwinkles that indicate it was likely to have been sourced from Portsmouth beaches. Ballast in the hold would have also included the weight of ‘secondary ballast’, from two large brick ovens in the galley and their log fuel. This adds further considerations to the calculation of the ships weight.

Today, ships are balanced with water; pumps and measurements ensure the ship remains a perfect weight to sail safely. Water is now pumped out automatically to adapt to the ships weight; a much easier method than the Mary Rose crew were used to! But the transition between gravel and water also included the development of other solid ballasts including stone, sand, old guns, unused shot as well as construction rubble and iron bars.

Though iron ballast was not used until 200 years after the Mary Rose, it still plays an important role in conserving the ship today.

Conservation of timbers from the Mary Rose and her objects is carried out in what is known as the Cable Test House of the dockyard; a Victorian building once used for testing the strength of cable and chains for anchors. Today it acts as a workshop behind the scenes for the staff of the Mary Rose Trust to carry out important work in caring for the ships 19,000 objects. All of this is done over a vast floor made almost entirely of pig iron ballast bars.

Pig iron became commonly used in the Navy as a form of ballast in the early 18th century. Though sometimes referred to as iron pigs, they are 3ft long bars, much less exciting than actual miniature pigs but still equally as useful. Pig iron ballast was easier to move manually, and their uniformed weight made calculations much quicker for the sailors.

The “Po” stamped into each bar mark their origins in Portsmouth; much like the ballast of the Mary Rose, these were locally sourced and once again show how important Portsmouth has been in the history of naval ships.

Another example of ballast, demonstrating how it can be repurposed, can be seen on College Road in Portsmouth Historic Dockyard. Upon entering the Historic Dockyard, turn right past the Porter’s Gardens to view the “Pique Stone”. This piece of ballast from HMS Pique, was famously used to cover damage in the hull to prevent further leaks after the ship ran ashore in 1835. Today it stands as a reminder of the resourceful sailors using stone ballast to ensure the durability of their ships.

As ballast continues to have a valuable role in maintaining the safety and buoyancy of a ship, the weight of the Mary Rose ballast remains a topic today. A ship’s weight must be calculated perfectly to ensure the correct amount of ballast is used. Could a miscalculation of the ship’s weight have been a contributing factor in the sinking of the Mary Rose? Could a stone or two have played a role in the fate of the ship? Whether this is true or not, ballast, despite often appearing as a pile of rocks, is evident in the history of ships, connecting the Mary Rose to Portsmouth dockyard today.