Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Designation | Bore | Weight | Service Charge | Range (yards) | Number Made |
| --- | --- | --- | --- | --- | --- |
| 12-pdr small | inches (cm) | pounds (kg) | — | — | 23.0 |
| 12-pdr light | inches (cm) | pounds (kg) | ounces (g) | — | 177.0 |
| 12-pdr heavy | inches (cm) | pounds (kg) | pounds (kg) | yards (m) at 5° elev. | 456.0 |
| 12-pdr rifled | inches (cm) | pounds (kg) | pounds (kg) | yards (m) at 6° elev. | 424.0 |
| 24-pdr | inches (cm) | pounds (kg) | pounds (kg) | yards (m) at 11° elev. | 1009.0 |
Question:
What is the bore of the boat howitzers with a 12-pdr heavy designation?
Answer:
inches (cm)