The Cannon

After multiple attempts, the cannon was successfully recovered and is currently in the process of restoration.

35°16’.089 S

174°07’.221 E

Once the story of the lost cannon was identified, it was immediately obvious that the rum being made at Kororāreka would become “Sunken Cannon”.

RECOVERY

It also did not take long before a plan was hatched to search the vicinity of Mill Island for this cannon. 

Underwater searches of Mill Island had been attempted in 1980 by Kelly Tarlton and later in 2018 by New Zealand Underwater Heritage Group.

The original references talked of a cannon being on the island and secured to the Mill. The storm was said to drag the Mill and cannon into the sea. The search area inferred from this approach resulted in a number of fruitless searches, and the collection of many old beer bottles.

A change of search strategy adopted an assumption that the cannon was initially placed in the sea as a mooring, which in turn was secured to the Mill. This change of context, identified an alternative location to investigate.

Cannon on the seabed

In early 2023, two years of attempts by the team at Sunken Cannon came to fruition. A strong metallic signature was discovered in the location where a mooring would most logically be placed to  access Mill Island. 

Cannon located by metal detector

During 2023, the cannon was lifted and placed into a conservation bath alongside the rum at Sunken Cannon. Extensive concretions and marine growth were evident, but it was immediately recognisable as the cannon that had been used in the battle of 1845 and underwater for 166 years.

Cannon on sling underwater

CONSERVATION

For a period of 18 months a small current will be run through the cannon to reverse the corrosion and stabilise the metals.

Steel anodes in the bath provide fresh metal ions to be deposited into the cannon and drive out the embedded salt. A fascinating part of this electrical process was the bubbling of hydrogen from the cannon, with the outline of the cannon evident on the surface of the bath. The conservation bath is Sodium Hydroxide, added to fresh water to create a conductive solution with approximate ph13. This is changed every six weeks.

Reversing the corrosion

The Mill Island Cannon appears to be a 12 Pounder Carronade. It has a distinctive narrow muzzle and a nozzle within the bore to assist loading. This was a “ship smasher” style that achieved prominence in the 1805 Battle of Trafalgar. 

Conservation work on submerged metals suggest that 1 year of electrical stabilisation is required for every 100 years of salt water immersion. Using this metric, conservation work is expected to be completed in mid-2025.