Overboard (1987) plot summary
Joanna, a spoilt rich girl, hires a carpenter called Dean to make a closet for her yacht while it's stuck in port. He makes a really cool one, but she says that she wanted a different kind of wood and refuses to pay.
In the night, Joanna falls off the yacht and is picked up by the coast guard the next day- but she has lost her memory. Her husband hears about it, but, as he doesn't really like her and only married her for her money, he denies knowing her.
Dean hears about it and decides to get revenge by pretending that he's her husband, and makes her come cook, clean and take care of his three sons.
She actually turns out to be really cool, and the kids want her to stay, so even though Dean feels bad, he doesn't tell her the truth, because they're getting along so well.
Then, her husband shows up, but that's going into the ending...