New York Times: "Are crunches worth the effort?"

Apparently, evidence demonstrates that "ripped abs" are for "show" but there is a small caveat: Those with weak cores should strengthened them:

From The New York Times:

No one needs to perform hundreds or even dozens of crunches, said Brad Schoenfeld, a professor of exercise science at Lehman College in the Bronx and an author of a newly published review article about core exercises titled “To Crunch or Not to Crunch.” And while everyone needs some basic minimum of core strength — getting up out of a chair requires a certain amount of core strength; serving a tennis ball requires more – “six or eight crunches would be plenty,” he said, “and only a few times a week. ...”

There is also a procedure in the New York Times article as to how one can do a correct sit-up without injuring lumbar or cervical discs. The abstract linked to above says crunches are not friendly to spine health.

The question is, how important is it to have a "ripped" core for swimming?

This study listed at the National Institute of Health seems to support that there comes a time when your core is strong enough:

Abstract: Development and validation of a core endurance intervention program: implications for performance in college-age rowers.

The objective of this study was to examine the effectiveness of a core endurance exercise protocol. Forty-five college-age rowers (age 21 +/- 1.0) were assigned to either a core training group [core group] (n = 25), which took part in a core endurance intervention exercise protocol, or to a control training group [control group] (n = 20), which was not given any specialized core training. Training took place 2 days per week for 8 weeks. Trunk endurance was assessed using flexion, extension, and side flexion tests, whereas a variety of functional performance measures were assessed (vertical jump, broad jump, shuttle run, 40-m sprint, overhead medicine ball throw, 2,000-m maximal rowing ergometer test). The results revealed significant improvement in the two side flexion tests for the core group (p < 0.05). Interestingly, significant differences were noted in the trunk extension test endurance times for the control group (p < 0.05), but not for the core group. No significant differences were found for any of the functional performance tests. In summary, the 8-week core endurance training program improved selected core endurance parameters in healthy young men, but the effectiveness of the core intervention on various functional performance aspects was not supported.

[Link]

As for me I have never been happy with my core strength which could be the result of seeing too many "ripped abs" in billboards, magazines, beer commercials, and music videos. I suspect actually doing the sport you do will give you the abs you need unless it is running.