cast iron cannon

Can someone out there help me identify my old cast iron ship cannon. I purchased it from an estate. They had it at their St Croix home for decades. They said it was originally found in the Christiansted Harbor. While cleaning the cannon the only marking I could make out was P1767 which I believe...

I need help figuring out what this cannon is used for. I bought it at a auction in TX. The description said it was a race starter, but when I researched online I found that it could also be used as ship signaler????? Anyways it is pretty heavy I'd say around 20-25 pounds. It is 17.5 inches from...