* Net premiums up 6.5 pct to $2.04 bln
* Average weighted premiums down 3.2 pct
* Pretax profit up 118 pct to $318 mln
* Shares up more than 5 pct (Adds COO, analyst quotes; share reaction; details)
By Richa Naidu
LONDON, Aug 8 (Reuters) - Bermuda-based Catlin Group said first-half profit more than doubled as the insurer's geographical spread shielded it from weak pricing that has dogged its British rivals during the period.
Catlin's London-listed shares shot up more than 5 percent on Friday, making it the biggest FTSE-250 percentage gainer.
Rates of insurance against potential disasters have been either stagnant or in decline mainly due to increased competition and fewer large catastrophe claims over the past year.
Catlin said its exposure to "more resilient" pricing in the United States, Europe and Asia had made it less vulnerable to sinking rates in London and Bermuda, where wholesale and catastrophe reinsurance lines dominate the market.
Bermuda has no corporate income tax, which has helped it become a major centre for reinsurance companies, which help insurance firms cover claims from major events such as earthquakes or floods in exchange for part of the premium.
"Nearly 50 percent of (underwriting) now comes from non-London hubs," Chief Operating Officer Paul Jardine told Reuters.
"We are getting access to business that quite frankly is at better pricing levels than we might see in our more traditional hubs of London and Bermuda. And that's a differentiator."
Catlin, which operates the biggest syndicate in the Lloyd's of London insurance market, said net premiums earned increased by 6.5 percent to $2.04 billion in the six months ended in June, even though average rates decreased 3.2 percent across its portfolio.
Rates for catastrophe-exposed business classes decreased by 6.4 percent, while rates for non-catastrophe classes fell by only 0.1 percent, the company said.
"Catlin reported the strongest set of numbers across its peer group so far," Barclays analyst Andy Broadfield wrote in a note. "What Catlin is repeatedly demonstrating, and what is so important at this early stage of the softening environment, is the benefit of a diversified and 'value adding' business model."
Barclays has a "equal rate" rating on Catlin shares, which were up 5.3 percent at 0928 GMT.
Catlin's peers, including fellow Lloyd's underwriters Amlin and Hiscox and insurance broker Jardine Lloyd Thompson, have all warned on the impact of softening prices.
Pretax profit rose 118 percent to $318 million, helped also by better investment returns and a "relatively benign" first half for claims.
Catlin posted a combined ratio of 85 percent, down from 88.1. A ratio below 100 percent means an insurer earns more in premiums than it pays out in claims.
The underwriter, which covers risks ranging from aviation and marine to kidnapping and livestock, said it took hits totalling $31 million from the missing Malaysia Airlines flight MH370, a U.S. barge collision and a fire at an offshore drilling rig.
It said it would incur a loss of less than $50 million from the downed Malaysia Airlines flight MH17 and aircraft losses from violence at Tripoli's international airport last month.
Catlin's investment return for the period rose to 1.6 percent from 0.2 percent, while the company raised its interim dividend by 5 percent to 17.7 cents. (Reporting by Richa Naidu; edited by Yousra Elbagir and Simon Jessop)