The permanent cruise

A number of years ago, Lindquist of Northwestern met some older travelers on a Caribbean cruise who had essentially retired on water -- even though they shared the same sorts of health problems as her patients living in assisted-living facilities.

That gave her the idea to compare cruise-ship living to assisted living. She concluded in a paper published in an academic journal in 2004 that the costs are about the same, and many of the amenities and services line up as well: dining, escorts to meals, help with medicine and housekeeping.

In between trips, they might stay with family, or in a hotel.

Ralph Ponce de Leon, a 78-year-old retired Motorola executive who lives in Phoenix, spends at least one-third of every year seeing the world aboard Carnival's Holland America line with his wife, Kathie.

On their first cruise with the company, he says, he was surprised to see a number of passengers in their 90s, including a 92-year-old from the United Kingdom who told him she had taken 18 world cruises, which can last as long as four months.

One big advantage on a cruise ship: "You have a 24/7 physician and nurses," while doctors aren't always on-site at an assisted-living facility, Lindquist says.

It isn't clear how many people already are living on cruise ships full time, but more than 400 people reached out to Lindquist after reading her paper, she says, many of whom planned to attempt it. The costs of the two choices have remained roughly the same since, she says.

Spa living

Portnoy of Miami Beach isn't the only person who used a spa instead of an assisted-living facility. Melinda Minton, the executive director of the Spa Association in Fort Collins, Colo., says others are beginning to connect the dots.

One reason: Spa resorts increasingly are trying to expand into residential communities, "so you have people typically your age and in the same phase of life as you are," she says.

Meanwhile, Portnoy says, a friend's mother recently moved into Canyon Ranch, and he has talked to more people who live at the resort part time, or have vacationed there, and are considering similar arrangements with their own parents.

For other adult children considering such a move, he cautions that there were times when he felt he was in over his head, particularly in hiring nursing aides. But Canyon Ranch's medical and wellness teams "couldn't have been more supportive," he says. "They embraced me in what I was trying to do."

Of his mother, Portnoy says, "I think she lived much longer than she would have if she'd been in an institution."

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