A cruise ship leaves port in Le Havre, France, Jun. 20, 2017. Getty Images

A cruise ship might seem like an isolated safe haven, but luxury liners may actually pose “hidden dangers” such as the risk of sexual assault. Due to a confluence of factors, most sexual assaults on cruises are barely investigated or never prosecuted, according to a report released Wednesday by NBC News.

More than two-thirds of the 92 alleged criminal incidents aboard cruise liners last year were sexual assaults. One in three of those incidents involved victims who were minors, according to a congressional report.

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“It happens more often than cruise lines will admit,” Miami attorney Jim Walker told NBC News. “A lot of times the victims will be so confused, so shocked, they’ll actually leave the ship without reporting it on the ship. And I think crew members are kind of banking on that possibility.”

A cruise ship leaves port in Le Havre, France, Jun. 20, 2017. Getty Images

Jurisdiction issues often throw a wrench into sexual assault cases: the ship might be in international waters but registered in a different country and the situation might involve a suspect who is foreign.

“There’s not law enforcement on these ships,” said Walker. “So when a crime occurs the reporting has to be done to the cruise ship security. There’s a conflict of interest, of course, in having the security investigating a crime that involved one of the ship employees.”

While the FBI told NBC it couldn’t discuss specific incidents, it did claim that such crimes on ships pose “significant challenges for investigators.”

“I think the biggest disappointment were the actual FBI,” Anne Smith, whose 16-year-old daughter said she was sexually assaulted by a gym trainer on Carnival Cruise, told NBC News. “They took a brief statement from both of us and pretty much made it clear that there wasn’t gonna be much after that.”

Travelers could only begin accessing official crime statistics from cruise ships in 2016, when concrete numbers were finally released. A report issued in October showed that sexual assaults on cruise ships increase 550 percent in the first six months of 2016, while overall crimes reported on ships increased 408 percent.

“If you go back three years ago, when we raised the question with the FBI: ‘What are you going to do if someone is raped on the high seas?’ The answer was, ‘Nothing,’” Kendall Carver, founder and chairman of the International Cruise Victims Association, told Arizona Central in 2016. “Now they are doing something.”

Laws passed in 2014 made mandatory public disclosure of all serious crimes that occurred onboard cruise ships. The FBI also put in place a system that would put victims in contact with a federal agent while they were still on the cruise.

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The cruise industry, however, maintained that ships were safe. Michael McGarry, Cruise Lines International Association senior vice president for public affairs, told NBC News that the number of sexual assaults on board ships was a “small fraction of the comparable rates of crime on land.”

“We are unaware of any case where a cruise line did not report an alleged serious crime as required by law. Out of a strong duty of care for guests, cruise lines are motivated to ensure that any allegation of a crime is immediately reported. Cruise lines have every incentive to ensure a safe and enjoyable holiday experience for all passengers and therefore continually access improvements to passenger security and safety.”

A cruise ship docks in London, England, May 5, 2016. Getty Images