“When my ship comes in” is an idiom meaning “when my fortune arrives.” People who have bad luck (and who doubt that their ship ever will come in) have added an extra ending to the saying. “If your ship doesn’t come in, swim out to it” (or, “If you ship doesn’t come in, swim out to meet it”) is a variation that has been printed on many images. ” If your ship doesn’t come in, swim out to it!” was printed in an October 1990 newspaper.
 
“‘If your ship doesn’t come in, swim out to it.’—JONATHAN WINTERS” was printed in an October 1991 newspaper. American comedian Jonathan Winters (1925-2013) is usually credited with the line, but it’s uncertain when he first said it.
     
         
Wikipedia: Jonathan Winters
Jonathan Harshman Winters III (November 11, 1925 – April 11, 2013) was an American comedian, actor, author, and artist. Beginning in 1960, Winters recorded many classic comedy albums for the Verve Records label. He also had records released every decade for over 50 years, receiving 11 Grammy nominations, including eight for Best Comedy Album, during his career.
 
The Free Dictionary
when one’s ship comes in
Fig. when one becomes rich and successful.
 
(Oxford English Dictionary)
when one’s ship comes home (or in), when one comes into one’s fortune.
▸?a1513   W. Dunbar Tabill of Confessioun in Poems (1998) 273   Thou mak my schip in blissit port arrive, That saillis heir in stormes violent.
1851   H. Mayhew London Labour I. 175/1   One [customer] always says he’ll give me a ton of taties when his ship comes home.
1886   D. C. Murray Cynic Fortune xii,  The wealthy relative..proposed to supply him with an income of a hundred pounds per annum until the major’s next expected ship should come in.
         
18 October 1990, The Current Local (Van Buren, MO), “Carter-Butler County Line News” by Jean Carter, pg. 11, col. 4:
Thought: If your ship doesn’t come in, swim out to it!
 
9 December 1990, Florida Today (Cocoa, FL), “Sharon Masson—Cocoa High,” pg. 12D, col. 3:
If your ship doesn’t come in, swim to it.
 
6 October 1991, Star Tribune (Minneapolis, MN), pg. 9J, col. 8 classifieds:
Weekly Quote: “If your ship doesn’t come in, swim out to it.”—JONATHAN WINTERS.
 
27 September 1992 The Post and Courier (Charleston, SC), pg. 7-F, col. 8:
“If you ship doesn’t come in, swim out to it.”
—Jonathon Winters
 
22 December 1992, The Times (Munster, IN), “Interesting thoughts and tips to help motivate ourselves” from James Sherman of Hammond, pg. D-10, col. 1:
5. If your ship doesn’t come in, swim out to it.
   
Google Books
How Do You Want Your Room—Plain Or Padded?:
Sanity-preserving Tactics for Today’s Woman
By Jo Ann Larsen and Artemus Cole
Salt Lake City, UT: Shadow Mountain
1995
Pg. 209:
“If your ship doesn’t come in, swim out to it!” (Jonathan Winters.)
 
1 December 1995, Austin (TX) American-Statesman, “Street Talk” by Tom Green and Bruce Hight, pg. D1, col. 5:
Also, “If your ship doesn’t come in, swim out to it,” from Jonathan Winters.
 
philosiblog
If your ship doesn’t come in, swim out to it!
by Philosiblog on 14 May 2013 in action, common sense, humor, procrastination, reflection, wonder
If your ship doesn’t come in, swim out to it! – Johnathan Winters
   
Facebook
Jack Canfield
July 5, 2013 ·
“If your ship doesn’t come in, swim out to meet it.” -Jonathan Winters
 
Google Books
Words of Power:
365 Inspirational Messages, Spiritual Powerlines, and Prayers
By Jeanne Alcott
Bloomington, IN: WestBow Press
2014
Pg. ?:
If your ship doesn’t come in, swim out to meet it.—Jonathan Winters.