LONDON (Bloomberg) — Bermuda-based Frontline Ltd., the world’s biggest oil-tanker owner by capacity, said it will convert a vessel into a heavy-lift ship to benefit from rising oil-rig construction.The tanker Front Target<$> will be converted between May and August next year, allowing it to be used for 15 years, Hamilton, Bermuda-based Frontline said yesterday in a statement to the Oslo Stock Exchange. Front Targ$> will be converted by China’s Cosco Shipyard Group Co., Ltd.

There are a “limited number” of heavy-lift vessels available, Frontline said. Demand for the ships to transport oil-rig parts is increasing as a rally in crude prices over the past five years spurs oil companies to boost production and exploration. Tanker owners are also up against a 2010 deadline when some of their ships will be banned from carrying oil.

The ship Frontline is converting has only one layer of steel separating its cargo from the ocean so it carries a greater risk of spillage in the event of an accident. Such vessels are due to be banned from carrying oil under United Nations-led rules that come into force in 2010 and take full effect five years later.

Frontline had an option to convert Front Tar<$>. It has a further four options to convert tankers to heavy-lift vessels, and is looking for more, Oscar Spieler, chief executive officer of Sea Production Management AS, a Frontline unit dedicated to converting single-hull tankers, said by phone from Oslo yesterday. Another ship, Front Sunda, is due to be delivered from a conversion yard next year.

Shares of Frontline dropped two kroner, or one percent, to 198.5 kroner as of 9.13 a.m. in Oslo. They have slipped 21 percent this year, valuing the company at 14.9 billion kroner ($2.42 billion).