How to survive if you fall off a cruise ship in the middle of the ocean, according to a survival expert

• James Michael Grimes survived nearly 20 hours in the open ocean after going overboard a cruise ship.
• An expert told Insider the main concerns for someone adrift in the ocean and how to deal with them.
• Not panicking, trying to find objects that float, and making a signal can help you survive.

If you fall from a cruise ship in the middle of the night and no one knows, there are a few things you can do to boost your chances of surviving and of being found, according to a survival expert.

James Michael Grimes found himself in this exact situation on Thanksgiving Day after he went overboard on the Carnival Valor cruise ship the night before. The 28-year-old told ABC's "Good Morning America" he didn't remember falling, only waking up somewhere in the Gulf of Mexico with no boat in sight.

Grimes described the next 20 hours as a fight for his life spent treading water while fending off jellyfish and at least one unidentified finned creature. He made it through the night and the next day, until night came again, and tried eating objects that floated by, including a piece of bamboo.

He was finally spotted by crew aboard the bulk carrier vessel Crinis and was eventually rescued by a Coast Guard helicopter.

US Coast Guard Lt. Seth Gross, who oversees search and rescue missions in the greater Louisiana Gulf Coast area, told Insider a "whole bunch of factors" had to work out "perfectly" for Grimes to have survived the ordeal: "To survive the fall, to be able to keep himself afloat, that no sharks ended up locating him, and then this motor vessel just happened to be in the right position."

But even if luck, tenacity, and the preparedness of the Coast Guard were key factors, there are some practical things a person who falls into the open ocean can do in order to increase their chances of surviving, according to Cat Bigney, a survival expert who has consulted for Bear Grylls and National Geographic.

Don't panic

There are many things working against a person who goes overboard. First, they have to avoid injury during the fall and when they hit the water. Calling for help or actually finding help in the open ocean is just about impossible. There could be blazing sun, potentially hungry predators, and rough water. Hypothermia and dehydration are also major risks.

"All of these factors make it very difficult for people to survive if they're adrift," Bigney, who has taught at the Boulder Outdoor Survival School for decades, told Insider.

Going overboard on a cruise ship is extremely rare, but the vast majority of those who do are never rescued. Between 2009 and 2019, there were 212 overboard incidents on cruise ships, according to data compiled by Cruise Lines International Association. Only 48 of those people were rescued.

But the first thing a person in an overboard situation needs to remember? Don't panic.

"When people enter into a body of water they usually damage their lungs right away, because they gasp," Bigney explained. "We have such a panic instinct to get air, and when people do that they bring water into their lungs."

Keeping your cool in life-or-death situations is key, as panicking is "the biggest thing that will kill you in a survival situation," according to Bigney.

Find anything that floats

Once you're in open water, your next priority is to stay above the surface. Some people may have a natural advantage and float more easily, depending on their body composition, including body fat percentage and muscle mass.

Though Grimes was in the water for around 20 hours, it's unlikely he was treading water for that entire time, according to Bigney. A combination of floating, treading, and swimming would be ideal, although it would still be exhausting, especially in rough waters. But treading water periodically is still much more doable than constantly.

There are also ways to make floating easier. For instance, Grimes said he had taken off all of his clothes, in order to make himself more buoyant.

"Even a small buoyant device will help you — something you can use with your arms around or your neck over just to help relieve some of the stress if you're not a great swimmer or you're having a hard time staying afloat," Bigney said.

Grimes had said he tried chewing on some bamboo, which Bigney said is extremely buoyant. Even collecting small bits of bamboo or driftwood could help a person stay afloat, she said. In a best-case scenario, you could collect enough that would allow you to make a pile or raft that you could get up on top of and out of the water, which would also make you safer from any potential predators. 

Water would be a concern, food not so much

It's unlikely Grimes was able to get significant energy from chewing on bamboo, but food would not be a primary concern in the amount of time he was at sea.

"Our bodies are perfectly, evolutionarily adapted to have this ability to fast for a long period of time, so he should have been fine as far as food," Bigney said, adding that "psychologically" it may have helped him, but "physiologically" his body was probably okay without eating.

Calories are needed to regulate core body temperatures, but she said most bodies would be able to do that for a couple of days with reserves, including from fat and the liver. Grimes was treated for hypothermia after he was rescued, as the 70-degree water temperature was significantly colder than humans' baseline core body temperature, but moving around and swimming for much of the time he was stranded — as well as factors like what he had recently eaten and his body fat content — may have helped him avoid the worst of it.

Dehydration would be of a much greater immediate concern than food, according to Bigney.

"You don't want to drink any salt water," she said, adding that you'd want to try to conserve whatever water you already had. One way to do that would be to try and use your clothing to create shelter from the sun, such as by wrapping it over your head.

Make a signal however you can — including with trash

Ultimately, if you fall from a cruise ship many miles from shore, it's a waiting game to be rescued, and making a signal is one way to improve your chances of being found.

"There's a lot of trash in our great oceans, unfortunately," Bigney said, adding that collecting any floating garbage into a large pile could potentially form a signal that could be spotted by rescuers.

When an overboard situation is reported, the US Coast Guard uses a program to estimate where a floating object might be, Gross told Insider. The Search and Rescue Optimal Planning System factors in the person's weight, clothing, body fat percentage, and whether or not they have a flotation device, as well as weather and ocean patterns.

For Grimes, the system returned over 7,000 square nautical miles of ocean where he could be, which is about the size of Massachusetts — so anything you can do to increase the chances of being spotted can help.

"In the end, it's kind of a grim situation, but people have survived," Bigney said, adding: "And people sometimes just die."

Have a news tip? Contact this reporter at kvlamis@insider.com.