The 'stealth zone' is one of many safety measures to protect sailors from the threat of piracy off the coast of Somalia [GALLO/GETTY]

French team Groupama became the first boat to reach the so-called "stealth zone'' of the Volvo Ocean Race on Thursday, an area where the yachts can not be tracked by the public as they head for an undisclosed location to avoid possible pirates.

Groupama was more than 80 nautical miles ahead of the other four boats in the second leg of the round-the-world race, organisers said, as the yacht slipped into the area where the boats positions will be kept secret from the public.

"It's fast and noisy and very wet, with a lot of water on deck,'' said skipper Franck Cammas, who will celebrate his 39th birthday on Thursday.

"The helmsmen love steering in these conditions.''

American team Puma were second, followed by overall leaders Telefonica in third, Camper in fourth and Abu Dhabi in fifth.

Safety measures

The boats set off from Cape Town and are headed for a secret "safe haven'' port, from which they will be transported to a location near Sharjah, United Arab Emirates, before continuing toward Abu Dhabi.

The stealth zone and undisclosed port are part of the measures to avoid pirates off the coast of Somalia.

The teams are expected to arrive at the port in the next seven to 10 days, with the leg finishing in Abu Dhabi sometime next month.

Chinese team Sanya was forced out of the current stage of the 39,000-nautical mile race, which will finish in July next year, because of a rigging problem.

The boat is undergoing repairs in Madagascar, with the team planning to resume the race in Leg 3 to their home port of Sanya.