Leary was among those on a "pretty chocka" boat which left at about 7.35am. The delay would make her late for a meeting in Hamilton.
She said there was none of the violence or abuse of ferry staff that had been reported last month - just "laughter and rolled eyes and 'Here we go again'".
Leary called for the return of a second operator on the Waiheke run, saying the service was better when there was competition.
Explore withdrew in 2016, leaving Fullers as the sole ferry provider for Waiheke.
Commuters last month said tensions had been rising since Fullers switched from half-hourly sailings in summer to its winter schedule with hourly sailings at off-peak times and reduced spaces on its boats, resulting in passengers being left behind.
Fullers chief Mike Horne said today, "This morning our crew aboard the 6am ex-Auckland service to Waiheke on board Quick Cat was notified of an engine-cooling issue mid-journey.
"... we made the decision to turn the vessel around at Bean Rock and return to Auckland where we immediately transferred the 23 passengers on board the Korora for the 7am departure. This delayed the journey by an hour but was the safest and most efficient solution to an unforeseen issue.
"The 7am ex-Waiheke Quick Cat service was subsequently cancelled and approximately 100 passengers who had been due to travel then boarded the 7.30am service aboard the D5, our replacement vessel immediately deployed upon news of Quick Cat's earlier issue.
"We know these cancellations impact the day-to-day life of our customers and sincerely apologise for the inconvenience this may have caused."
The Quick Cat was now being repaired.
"We're running a four-boat service today, which allows a half hour departure schedule for peak commuter periods and do not foresee any other impact to services."
Horne defended the quality of Fullers' Waiheke services, highlighting its statistics for May:
• 1384 services in total.
• 18 cancellations.
• 10 cancellations related directly to weather events, for example fog and unsafe weather.
• 8 cancellations due to unforeseen operational issues.
Horne said the last point on that list "is our current focus".