David and Petulia have sailed their yacht to Peru and we see them relaxing at a marina somewhere south of the border while a radio station chatters away in Spanish in the background.
Then ... But sombreroed locals and a few potted palms dotted about didn't fool CitySleuth. This scene was filmed at Kappas Marina in Sausalito (map), just north of San Francisco! Check out what appears to be a causeway at upper right and a mountain slope behind it in the composited panorama below.
... and Now, the causeway is Highway 101 crossing Richardson Bay and the mountain, fully revealed under clear skies, is Mount Tamalpais. The hills behind Sausalito are in the left background.
Then ... Here's an aerial photo of Kappas Marina taken in 1968, the year Petulia was filmed.
... and Now, compare it with the marina today, now called Richardson Bay Marina, as captured in the Google satellite view below. The marina has been renovated and expanded and a houseboat community, retaining the Kappas Marina name, has been built between it and the adjacent Highway 101.
Below deck, David is overcome with self-recrimination. "Only a crazy man can hit a woman ... or a coward". He commits never to do it again and Petulia, believing him or not, forgives him.