A week ago, 2,600 passengers boarded the Star Princess on Seattle's waterfront. Among them was a 15-year-old boy traveling with his grandmother. The boy says along the way, he was sexually assaulted by another passenger in the sauna.

When the Star Princess docked in Skagway, Alaska troopers arrested 61-year-old John Johnson from Pacific, Washington. Prosecutors charged him with first degree sexual assault and sex abuse of a minor.

"We've had a number of sexual assaults on board cruise ships... it's not a unique situation," said Alaska State Trooper spokesman Greg Wilkinson.

Wilkinson says troopers have investigated three other cruise ship sexual assaults. And, Alaska prosecutors say the assaults have dramatically increased the past decade.

The problem got national attention in 1998 when a Carnival Cruise engineer raped a ship's officer. The investigation revealed 108 sexual assault accusations over a period of 5 years onboard Carnival ships.

Former Carnival employees said there was pressure to keep accusations secret. But the investigation changed that, and all cruise companies agreed to report alleged assaults to local police.

That's exactly what Princess Cruises says it did this week in Alaska.

"Cruise ships are considered one of the safest forms of vacation as you have a very closed -- close and closed -- community where all the passengers are known... all the crew is known," said Julie Benson, a Princess Cruises Spokeswoman.

We've also learned that John Johnson is known to police here in Washington. In King County he was arrested in July for indecent liberties. And in 2000, he was arrested in SeaTac for indecent exposure and loitering.

He's in court in Alaska next week.