I put about 8” of water in my boat last year. It was leaking a lot. The plug wasn’t tight enough. The screws though the transom for the transducer. Lots of rivets and must be a crack under the keel. Paint can stop some of the leaks. I put some silicone on it and I’m going to get a second bildge pump. It gets water in it when it rains anyway.
keep working on it you’ll get it stopped.