It did not fill up completely.
Just this weekend, the admiral was complaining how tipsy the boat was and she asked me if I was sure that the ballast was completely full. "What a stupid question" I thought, but I know that every time she opens her mouth, she happens to be right. I inserted a stick on the hole and it came out dry!!!I knew that I left it filling for about 15 minutes and normally it takes about 5 minutes to totally fill up. When I opened the screw again, no water came in. I pushed the shaft down and water started rushing in. It seems that the in coming water created a vacumm and shut the flapper closed. I assumed that because the butterfly was totally opened, the tank would fill up completely but apparently, the weight of the screw was enough to shut flapper and it only filled partially.The admiral was right, one more time!!!