You guys all forgot an obvious one: "Sailing, sailing, over the bounding main..."
"Sea of Love" by Maurice Williams and the Zodiacs; also the Honeydrippers, that one-off project by Robert Plant, Jimmy Page and Jeff Beck.
Speaking of Led Zeppelin, how about "Down by the Seaside," a lesser-played cut from Physical Graffiti. And of course, there's "The Ocean."
"Sail On" by The Commodores (a bit wimpy but it fits).
A one hit wonder called Every Mother's Son did a song called "Come on Down to My Boat."
"Ships" by Barry Manilow (another wimpy one but you won't find a title that's more to the point). And one more wimpy one, if you can hang in there: John Denver did a song about Jacque Cousteau's boat "Calypso."
If you're in a metal mood, "Children of the Sea" by Black Sabbath might be the best Ronnie James Dio-era Black Sabbath song. His own group Dio later did a little-known but absolutely marvelous song called "All the Fools Sailed Away."
Iron Maiden's epic (nearly 14 minutes long) "Rime of the Ancient Mariner." The live version on Live After Death really smokes! They also did a song called "Sea of Madness."
An obscure cut on Deep Purple's Burn album is called "Sail Away." After Ritchie Blackmore quit Deep Purple, he formed his own band Rainbow and their song "Catch the Rainbow" on their debut album has a line about sailing away "on ships of wonder."