Another reason it won't sink the boat (even though this fitting is below the water line) is because that hose leads to the raw water pump impeller. If the impeller/engine isn't running water won't flow. If the engine WAS running, and boat was not on plane, then this is below water line and the pump would pull water in through the open connection near the fitting. If on a plane, pump would be sucking air and impeller would burn up and engine overheat. Either way - not sinking (but not good either).