What is the joke in Simpsons where Homer has rat poison a boat and baby?

The joke is that Homer, despite being a bumbling fool, is able to figure out how to use a boat and a baby to create a makeshift submarine. This is in contrast to his usual behavior, where he is often unable to perform even the most basic of tasks. The humor of the joke comes from the unexpectedness of Homer's success, as well as the absurdity of the situation itself.