By Daniel Emery
Technology reporter, BBC News
The Sirius Star's cargo has an estimated value of $100m
The hijacking of giant Saudi oil tanker Sirius Star has focused the world's attention on piracy.
In the past five years, the number of piracy attacks around the world has fallen from 452 incidents in 2003 to 282 in 2007.
But it is a different story off the coast of Somalia; pirate attacks have increased by 100% in the past year.
The Sirius Star is the biggest tanker ever to be hijacked, with a cargo of 2m barrels of oil worth more than $100m.
But other than arming crews - a move opposed by ship owners and maritime organisations alike - what measures can be put in place to keep ships, their crew, and cargo safe?
Long-Range Audio Device (L-RAD) and Magnetic Acoustic Device (MAD) are pieces of equipment that many ships are now starting to deploy. Classified as a 'non lethal' weapon they create a beam of sound that can travel far further than sound from a normal loud speaker.
Vahan Simidian CEO of HPV Technologies, who developed MAD, explained how it all worked.
"We create our sound through what we call a plane sound source of information, which means a message can be heard a long way away.
The long throw planar magnetic speaker can be heard miles away
"If the captain had concerns about a vessel, they would activate siren mode on the MAD. That will definitely get their attention. You would then tell them that you know that they are there, and that they do not have the element of surprise.
"Should they keep on closing, the captain would commence evasive actions and switch on 'tone' - this is a piercing sound that will irritate and disorientate them," he said.
Currently they are used to communicate to a potential attacker that the ship knows they are there, but experts say that on full power it could knock someone off their feet.
"For now, the speakers on a merchant vessel aren't capable of hurting a person. Is our technology capable of hurting someone? Absolutely," said Mr Simidian.
We don't advocate the use or carriage of weapons on board a vessel
International Maritime Bureau
Nick Davis, a former pilot who runs Anti-Piracy Maritime Security Solutions, an organisation set up to help protect merchant vessels, has three-man teams working on vessels in the Gulf of Aden.
He said that ships - and more importantly ship owners - need to take precautions to help themselves.
"There are certain types of ship that are liable to pirate attack. It needs to be slow moving - less than 20 mph - and have a low freeboard (that's the distance between the water and the deck)," he said.
"For vulnerable vessels, the usual measures employed when a ship leaves port is to hang barbed wire all the way round it, flood the ballast tanks, keep the fire hoses on full power and maintain a permanent deck watch.
"If any [small] ship comes within a mile, you sound the general alarm and crank up the Long-Range Audio Device (L-RAD) and get all the crew on deck."
Nick Davis said that having technology such as L-RAD or MAD, along with an alert crew, can make all the difference.
His team recently helped repel an attack on an 8,500 tonne chemical tanker.
"The team identified three boats coming at speed - once they got within a mile, they activated the piracy general alarm. The ship increased speed, and called local coalition forces on VHF.
"The L-RAD was activated and the crew got on deck. The pirates got within 400m brandishing weapons. However, we were sending warning tones via the L-RAD and eventually they withdrew."
Frequently though, crews will have to repel boarders. The usual method is to use a high pressure hose to try and push an assailant off the ship.
But a company in the Netherlands has come up with a simple solution: a 9000 volt electric fence. Secure Ship is a set of electrified guard rails surrounding the ship, which the manufactures say is similar to systems used to protect military installations.
The International Maritime Bureau manager Cyrus Moudi said that the Secure Ship system had its uses, but wasn't suitable for every ship.
"The electric fence is non-lethal and can help deter attackers. But it's not strictly safe and you cannot use it on vessels carrying flammable cargo. Electricity and explosive vapour is not a good mix," he said.
"We don't advocate the use or carriage of weapons on board a vessel. There are better ways of securing your ship. And the primary defence is having a good lookout."
The task of keeping a good lookout usually falls to radar, except when the crew is on alert. But many attacks are conducted in small vessels and spotting and identifying them is easier said than done, especially when wave 'clutter' can confuse radar.
But a technology development firm in East Anglia are working on a system that not only spots a target, but can identify it too.
The marine holographic radar can detect and image small targets
Gordon Oswald, technology director with Cambridge Consultants, who are developing the holographic radar, said that while the idea was still in its infancy, it had the potential to be a valuable tool for ships and their crew.
"The holographic radar looks all round a ship, rather than seating a beam in a 360 degree circuit. Which means you can continually observe the target and get more information on what it's doing, rather than having to plot a course," he said.
The device works on a fixed line of sight and would be used in conjunction with regular radar. But unlike other devices, it can form an image of its target, enabling the crew to actually see what the target looks like.
At least 12 vessels - including the Ukrainian freighter MV Faina carrying 33 tanks and other military hardware, which was seized in September - remain captive and under negotiation, with around 250 crew being held hostage.