Never mind! See update at bottom of post.
Otis's answer suggests that you are remembering "The Tunnel Under the World" by Frederik Pohl, which was originally published in Galaxy Science Fiction, July 1955. That is quite a famous story; you can read it at the Internet Archive or Project Gutenberg or listen to a reading at Librivox or listen to the X Minus One radio play from 56-03-14. That story was also the answer to this old question and this one.
I'm sure Otis is right; the part about the boat clinches it, that is from "The Tunnel Under the World". Also, the story begins "On the morning of June 15th . . .", so it could have been titled "The Ides of June". However, there is another story which fits some of your data points better than the Pohl story: there is a day of the week in the title, it was an Analog story, and its magazine appearance was somewhat closer to the 1970s. Could it be that you read both of those stories and have conflated them?
The story I'm thinking of is "All Day Wednesday" by Richard Olin, originally published in Analog Science Fact & Science Fiction, March 1963; you can read it at Project Gutenberg. There is no boat, but like Pohl's story it's about an endlessly repeating day:
Ernie shook his head again. "Wait a minute. Let me get my head clear—O.K., now you say everybody is in some kind of trance. Why?
"I tried to make you see it today. The world is stuck. It's stuck in this God-forsaken one day! We don't know why. Some of us—just a few—have known it all along. But even we can't remember what caused it."
"You mean it's happening everywhere?"
"Yes. Or not happening, I guess you'd say. We're not getting reports from overseas . . . not any that are any different from the first Wednesday. So it must be the same over there. It's the whole world, Ernie."
[. . . .]
Ernie laughed scornfully. "You've got a good deal. Why louse it up? What do you stand to gain?"
Jory shook his head. "You're wrong, Ernie. For one thing, everything is slowly running down. Miners go to the same part of the mine each day and send out nothing but empty cars. The same thing is happening all across the country, in farms, in factories, in hospitals—"
Ernie got up. "Keep talking," he said.
"Hospitals are hideous these days, Ernie. Don't go near a surgeon. All he can do are the same operations he performed on the first Wednesday. If you're the wrong height, the wrong weight, or just there at the wrong time, he'll cut you to pieces.
"Homes burn to the ground. And nobody tries to get out of them. The fire department is no good. It's stuck in that first Wednesday.
Update. You must have read "The Tunnel Under the World" in the 1975 collection The Best of Frederik Pohl. From Pohl's afterword titled "What the Author Has to Say About All This":
In 1954 Lester del Rey and I were writing a novel in collaboration, and it was taking forever. [. . .] So one day, when we were on the third draft of chapter six, or possibly the sixth draft of chapter three, I announced I needed a vacation, and I took a week off and wrote "The Tunnel Under the World." (I didn't call it that. I called it "The Ides of June," and I still like that title better, but it seems a little late, now, to change it back.)