Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_8 (bore VARCHAR, designation VARCHAR)

### Question ###
What is the bore of the boat howitzers with a 12-pdr heavy designation?

### Accurate SQL ###

SELECT bore FROM table_name_8 WHERE designation = "12-pdr heavy"