The hole on the inside of the fill area looks as tho someone pushed something sharp thru the overflow hole. The result is the coolant expands and bypasses the pressure seal in the cap and blows out around the cap as you describe.
If I remember correctly (which gets less likely as time passes), in days of yore, when your boat was built, we didn't have overflow tanks for the coolant. Or maybe I'm just remembering raw-water-cooled engines.