Platinum Underwriters Holdings Ltd sustained a net loss of $224.1 million for 2011 in a year when the company was hit hard by catastrophe claims.The company managed to scrape net income of $7.1 million in the fourth quarter, a result impacted by $55.4 million in losses relating to catastrophes throughout 2011, about $27.9 million of which was due to the Thailand floods. There were also net impairment losses of $13.1 million, net of taxes.“2011 was a challenging year for Platinum with catastrophe losses dominating our results,” Platinum CEO Michael Price said. “Our book value per common share was $47.59 as of December 31, 2011, a decrease of 5.2 percent for the full year.“The book value per common share reduction was muted relative to the return on equity due to strong performance of our investment portfolio on a total return basis and the favourable effects of buying back shares.”The results for the quarter include net premiums earned of $167.3 million, net favourable development of $27.1 million and net investment income of $29.8 million.Mr. Price added, “Absent major events in the insurance or capital markets, we expect relative stability in overall reinsurance rate adequacy in 2012. We believe we are well positioned to participate profitably in select reinsurance classes, prudently manage our investment portfolio, and continue actively buying back shares.”The company’s net loss broke down to $6.04 per share for the full year. The impact of catastrophe activity was the main factor in the 57-point rise in Platinum’s combined ratio for the year to 143 percent. The ratio represents the percentage of premium dollars spent on claims and expenses.Net investment income decreased by $8.5 million, or 6.3 percent.Shareholders’ equity was $1.7 billion as of December 31, 2011, a decrease of $204.6 million, or 10.8 percent, from $1.9 billion as of December 31, 2010.Book value per common share was $47.59 at the end of last year, a decrease of $2.61, or 5.2 percent, from $50.20 a year earlier.