user: Question: What is the bore of the boat howitzers with a 12-pdr heavy designation?
Columns: ['Designation', 'Bore', 'Weight', 'Service Charge', 'Range (yards)', 'Number Made']
Types: ['text', 'text', 'text', 'text', 'text', 'real']
Sample row: ['12-pdr small', 'inches (cm)', 'pounds (kg)', '—', '—', 23.0]
SQL:

assistant: SELECT "Bore" FROM "Table" WHERE "Designation" = '12-pdr heavy';