(1:07 p.m. EDT) -- Carnival Cruise Lines is enhancing its vacation guarantee, which promises passengers will enjoy their cruises or get 110 percent refunds and free return flights.

The Great Vacation Guarantee, which takes effect immediately, also includes complimentary ground transportation and hotel accommodations, if needed. Those interested in trying a different Carnival cruise will receive a $100 shipboard credit for a future sailing.

To invoke the guarantee, dissatisfied passengers must reach out to guest services within the first 24 hours from when the ship leaves port.

"Within a day's time you've had a real chance to experience the product and the service and make a decision as to whether it's meeting your expectations or not," Carnival's Chief Marketing Officer Jim Berra told Cruise Critic .

Passengers may invoke the guarantee for any reason. If the problem is something guest services can fix, it will offer to do so. But if passengers don't want a fix, don't believe their expectations are being met or just don't think Carnival is the right fit for them, Berra said the line will honor the guarantee, no questions asked, get them home from the first port of call and provide the 110 percent refund. If the return home violates the Jones Act, which prevents cruise passengers from traveling between two U.S. ports without also stopping at a foreign port, Carnival will absorb any penalties that may be incurred.

"We did do training to make sure crew understood how the guarantee works and how we want these interactions to take place at guest services," Berra said. "We're being relatively relaxed about this because we want to make it as consumer friendly and easy as possible," Berra said. It doesn't hurt, of course, that Carnival is very confident in the experience it offers.

The company hopes the guarantee will encourage first-time cruisers and experienced cruisers who have never tried Carnival to give the line a try. In the wake of high-profile incidents such as a fire onboard Carnival Triumph and an emergency diesel generator problem on Carnival Dream, Berra said Carnival recognizes potential passengers might have some concerns.

"There are a lot of questions, barriers and uncertainties about cruising," Carnival's chief marketing officer Jim Berra told Cruise Critic. "We believe this guarantee is a chance to show just how confident we are in our product and also give cruisers more peace of mind in selecting Carnival."

Berra told Cruise Critic that Carnival expects a tiny fraction of passengers to use the guarantee, even factoring in passengers who might abuse it. "We do a lot of research around guest satisfaction, and the vast majority of our guests are very satisfied with their experience, and we expect that to improve as we make further investments in our product."

In an interview, given in 1998, two years after the original vacation guarantee was created, former president and CEO Bob Dickinson said only one-tenth of one percent of passengers had used the guarantee.

With the heart of hurricane season looming, Berra acknowledged bad weather could play a part in passengers deciding to use the guarantee. He said the benefits outweigh the risks. Passengers aren't only the ones to benefit, Berra pointed out. "This is important input for us as we try to continue to improve our product and our service experience. If we notice that the guarantees are being triggered by a particular issue, this gives us an opportunity to go in and address it."

The Great Vacation Guarantee is available to U.S. and Canadian residents on all three- to eight-day cruises to the Bahamas, Caribbean, Mexican Riviera, Alaska, Canada and New England departing through April 30, 2015.

--by Dori Saltzman, News Editor