Moving ship cannon into coastal forts

How often were cannon from a ship used in a fort?

Quite often, especially in coastal forts, where the same guns could stay on ship carriages anchored to the wall.

Naval and coastal artillery often used the same cannon. Near the sea, a gun could remain on its compact ship carriage rather than being transferred to a field carriage. Fort walls sometimes carried anchor points resembling those on a ship so recoil tackle could secure and run the weapon. That made it practical to lend guns from a warship to a siege or harbour defence, as Suffolk did during the Trincomalee operation. Common equipment and fittings connected naval firepower with operations ashore.