“A ship is safe in harbor, but that's not what ships are for.”

John Shedd, p. 81
They Both Die at the End (2017)

Source: Antigone, Line 163

This saying appears to be due to John Augustus Shedd; it was quoted in "Grace Hopper : The Youthful Teacher of Us All" by Henry S. Tropp in Abacus Vol. 2, Issue 1 (Fall 1984) ISSN 0724-6722 . She did repeat this saying on multiple occasions, but she called it "a motto that has stuck with me" and did not claim coinage. Additional variations and citations may be found at Quote Investigator http://quoteinvestigator.com/2013/12/09/safe-harbor/
Misattributed

Ch. 6.

Pt. 1: Bimini, Section 1 (the opening two paragraphs of the novel)
Islands in the Stream (1970)
Context: The house was built on the highest part of the narrow tongue of land between the harbor and the open sea. It had lasted through three hurricanes and it was built solid as a ship. It was shaded by tall coconut palms that were bent by the trade wind and on the ocean side you could walk out of the door and down the bluff across the white sand and into the Gulf Stream. The water of the Stream was usually a dark blue when you looked out at it when there was no wind. But when you walked out into it there was just the green light of the water over that floury white sand and you could see the shadow of any big fish a long time before he could ever come in close to the beach.
It was a safe and fine place to bathe in the day but it was no place to swim at night. At night the sharks came in close to the beach, hunting at the edge of the Stream, and from the upper porch of the house on quiet nights you could hear the splashing of the fish they hunted and if you went down to the beach you could see the phosphorescent wakes they made in the water. At night the sharks had no fear and everything else feared them. But in the day they stayed out away from the clear white sand and if they did come in you could see their shadows a long way away.

Source: The Best Advice I Ever Got: Lessons from Extraordinary Lives

Quoted in "American Caesar: Douglas MacArthur" - by William Manchester - 1978 - Page 195