Mercy Island

Mercy Island is a 1941 American drama that was nominated at the 14th Academy Awards, held in 1941, for Best Score of a Dramatic Picture, for which Walter Scharf and Cy Feuer received nominations.
Plot.
A young man takes his wife and a friend on a fishing trip to the Florida Keys on a boat owned by local "Conks". Following a blow on the head when their boat hits a shallow bottom and loses its propeller, the husband becomes mentally unstable and believes his wife is having an affair.