Pierce the ham all over with the tip of a sharp knife. In a 3 1/2 quart slow cooker, combine the port, broth and water. Add the ham, cover and slow-cook until a meat thermometer inserted into the center of the ham reads at least 165 F, 4 to 5 hours on low or 2 to 3 hours on high. Turn the ham once during cooking for even distribution of flavor. Transfer the ham to a platter and cover with aluminum foil to keep warm. Pour the cooking liquid into a medium saucepan, bring to a boil over high heat, and cook until the cooking liquid has been reduced to 2 cups, about 5 minutes. Stir in the raisins brown sugar and vinegar Reduce the heat to low and simmer for 5 minutes. Whisk in the cornstarch mixture and cook until just thickened. Pour the sauce into a sauceboar. Slice the ham and serve with the sauce passed on the side.