Charles Spurgeon Commentary Jonah 1:13

"Nevertheless the men rowed hard to get them back to the land; but they could not: for the sea grew more and more tempestuous against them." — Jonah 1:13 (ASV)

But they could not: for the sea wrought, and was tempestuous against them.

Their safety lay in the sacrifice—not in the labour. They rowed hard to bring the ship to land, but their efforts were of no avail. If they would cast Jonah overboard, then they would be safe.