Agatha Christie: And Then There Were None

For the propeller, you must first solve the hidden bookshelf puzzle in the office, then the safe puzzle in the secret room behind the bookshelf, and then the sliding panel puzzle in the room behind the safe. After you solve those three puzzles, there will be another passage after the sliding panel puzzle that will lead you to the grotto. The propeller is located on the rusty old broke down submarine.

For the fishing line, it's NOT on the beach where the General is ranting on about his Lesley. I can already tell you that you haven't been to the beach that it is on because you have to complete another puzzle first that requires the propeller in order to get an item to access the beach area where you get the fishing line.

I hope that I didn't spoil anything for ya and that this can guide you into the correct direction