Sembcorp Marine's Q2 net profit down 15 pct

* Q2 net profit S$149.7 mln; Reuters f'cast S$183.5 mln

* Secured S$2.6 bln new orders in 2011, orderbook at S$5.7 bln

* Shares down 1.3 pct in 2011, underperforming Keppel, market

SINGAPORE, Aug 2 (Reuters) - Sembcorp Marine , the world's second largest rig builder, posted a worse-than-expected 15 percent fall in second quarter net profit, despite stronger margins.

The company, a unit of waste-processor to infrastructure conglomerate Sembcorp Industries , said it has secured S$2.6 billion ($2.2 billion) worth of new orders so far this year excluding ship repair jobs, taking its total orderbook to S$5.7 billion.

The new orders come after a massive slowdown in the past two years as a result of the global economic crisis and a world-wide disruption in offshore drilling after an accident in the Gulf of Mexico led to an environmental disaster.

"The fundamentals driving the offshore oil industry remain intact with exploration and production spending by oil majors and national oil companies expected to increase in 2011," the company said in a statement.

"As offshore rig demand continues to strengthen in most regions around the world, there is a need for technically advanced, versatile and efficient rigs that will address both the shallow and deepwater prospects."

The company said the lower net profit was mainly due to timing in recognition of rig building projects.

Its earnings before interest, tax, depreciation, and amortisation (EBITDA) margin stood at 21.5 percent compared to 20.3 percent a year ago.