“Only a seaman realises to what great extent an entire ship reflects the personality and ability of one individual, her Commanding Officer. To a landsman, this is not understandable—and sometimes it is even difficult for us to comprehend—but it is so! A ship at sea is a different world in herself, and in consideration of the protracted and distant operations of the fleet units, the Navy must place great power, responsibility and trust in the hands of those leaders chosen for command. In each ship there is one man who, in the hour of emergency or peril at sea, can turn to no other man. There is one who alone is ultimately responsible for the safe navigation, engineering performance, accurate gunfire and morale of the ship. He is the Commanding Officer. He is the ship. This is the most difficult and demanding assignment in the Navy. There is not an instant during his tour as Commanding Officer that he can escape the grasp of command responsibility. His privileges, in view of his obligations, are almost ludicrously small; nevertheless, this is the spur which has given the Navy its great leaders. It is a duty which richly deserves the highest, time-honoured title of the seafaring world—Captain.”

Letter to the Naval Committee of Congress http://www.rulit.me/books/the-last-ship-read-334944-1.html (14 September 1775)

On American ships sighted sometime between 1801 and 1803, as quoted in The Royal Navy: Its Influence in English History and in the Growth of Empire https://books.google.com/books?id=mlNnAAAAMAAJ&pg=PA149 (1914) by John Leyland
1800s

Otto Neurath (1921), "Spengler's Description of the World," as cited in: Nancy Cartwright et al. Otto Neurath: Philosophy Between Science and Politics, Cambridge University Press, 28 Apr. 2008 p. 191
1920s

Employment of Naval Forces (1948)

Memorandum of February, 1588.
Conyers Read, Lord Burghley and Queen Elizabeth (London: Jonathan Cape, 1960), pp. 418-9.

Statement (March 1805) [citation needed]
1800s

Epilogue
The Flower of Old Japan and Other Poems (1907), The Flower of Old Japan
Context: p>Carol, every violet has
Heaven for a looking-glass!Every little valley lies
Under many-clouded skies;
Every little cottage stands
Girt about with boundless lands;
Every little glimmering pond
Claims the mighty shores beyond;
Shores no seaman ever hailed,
Seas no ship has ever sailed.All the shores when day is done
Fade into the setting sun,
So the story tries to teach
More than can be told in speech.</p

Captain Joel Chase, p. 15
Sharpe (Novel Series), Sharpe's Trafalgar (2000)

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