The passengers who were on Princess Cruises' Sea Princess will probably always remember the start of their three-and-a-half month round-the-world cruise, but not for the reasons you might expect.

The early days of the trip weren't notable for the gourmet meals, five-star staterooms or sophisticated deck parties, but because the ship had to go dark for 10 straight nights out of fear of pirate attacks.

The ship's crew was worried about pirates as the Sea Princess sailed through the western part of the Indian Ocean. About 1,900 passengers were on the 1,000-cabin Sun-class cruiser when the captain ordered cabin curtains be drawn and lights dimmed from sunset until sunrise for 10 straight nights. The blackout included a ban on music, movie screenings, deck parties and other nightlife events, which are usually a major part of such trips.

Passengers took part in a "pirate attack" lockdown drill, and the captain reportedly told them that crew members were ready with fire hoses and sonic boom equipment intended to disorient and unbalance anyone trying to climb onto the ship.

Despite the danger, the Sea Princess did not encounter any pirates and safely sailed through the Suez Canal and into the relative safety of the Mediterranean Sea.

AsukaII and Sea Princess at Yokohama Port in Japan The Sea Princess, like many cruise ships, is normally lit up at night. (Photo: Koichi Shibata/Wikimedia Commons)

Was there really a reason for the Sea Princess to worry?

Princess Cruises played down the incident, saying it regularly holds piracy drills when its ships enter dangerous areas. A spokesperson told the New York Daily News that despite the media focus on this particular instance, such security practices are common. "Any measures aboard Sea Princess were simply taken out of an abundance caution and not in response to a specific threat and are common to international shipping sailing in the region."

Perhaps Princess Cruises was right to play down the blackout. This was not the only example of a cruise line turning down the lights and music to avoid unwanted attention. The Telegraph reported that a P&O cruise ship called the Aurora had a similar blackout and pirate attack briefing with passengers as it passed the Horn of Africa earlier in 2017.

Hasn't piracy been defeated?

Royal Marines embarked aboard the Royal Navy frigate HMS Portland (F 79) investigate two suspected pirate skiffs in the Gulf of Aden Naval operations, like this one with Royal Marines in the Gulf of Aden, have helped to reduce, but not eliminate, piracy in the Indian Ocean. (Photo: U.S. Navy/Wikimedia Commons)

Piracy off the coast of East Africa used to be much worse, particularly in the Gulf of Aden where it was a major problem in the early 2000s. Pirates commonly targeted cargo vessels, but there were several incidents involving cruise ships, and even instances of private yachts being hijacked. The height of the crisis was in 2008, when more than 100 ships were attacked.

A multinational naval task force has been credited with making the area safer. Some countries, including Great Britain, have allowed armed guards on to ships as well. However, the hijacking of an oil tanker in March 2017 has signaled that piracy might be making a comeback after a decade-long lull.

What can ships do to limit the threat?

A dhow in the Gulf of Aden Most local boats in the Gulf of Aden are used for fishing, not piracy. (Photo: Mate 1st Class Robert R. McRill/U.S. Navy/Wikimedia Commons)

Anti-piracy strategies and practices have improved over the past two decades. During the worst year of the crisis, some cruise ships put grills over their portholes and strung razor wire or electrified barriers around the ship's body to keep anyone from climbing aboard.

Some boats have armed security personnel, but it's more common to see anti-pirate equipment such as high-pressure hoses, hoses that spray a slippery and irritating foam, and sonic weapons meant to disorient attackers with high-pitched noises. A British company has even developed a non-lethal laser that crews can shine on pirates to disorient them.

The captain of the Sea Princess assured passengers that his vessel could outmaneuver pirates if necessary. The speedboats favored by modern-day buccaneers are faster than cruise ships in calm water, but not in the rough, open ocean.

In 2005, a cruise liner operated by Seabourn Cruises came under attack in the Gulf of Aden. Despite using rocket-propelled grenades and machine guns, the pirates were not able to follow when the ship's captain took evasive maneuvers.

The most effective anti-piracy measure may be simple geography. Ships, even large ones, may only be visible from 10-12 miles away in open water. That's a long distance, but when you consider that the Indian Ocean covers millions of square miles, the chances of finding a ship with the naked eye, even if you know the general location of ship lanes, is slim.