Why did they cast lots?
Rashi citing Pirkei d'R. Eliezer 10: They saw other boats going serenely, and their boat was breaking. They said, it is due to one of us.
Radak: This is astounding. Why did they think that it is due to the people of the boat? Were there not other boats on the sea? Do all boats cast lots when there is a storm, to see who is the cause?! We can answer based on Pirkei d'R. Eliezer (refer to 1:7:1:1).
How can they rely on a lottery? It must fall on someone, even if no one is liable!
Malbim: They will cast many lots. If it always falls on the same person, either it is due to him, or he knows the reason for it. Therefore, they said "v'Nede'ah beshel'Mi ha'Ra'ah ha'Zos." Indeed, each time it fell on Yonah.
What is the meaning of "beshel'Mi"?
Rashi: Due to the deeds of which of us?