BERLIN » Pirates are capturing Germany’s political system.

The party with the outlaw name started as a marginal club of computer nerds and hackers demanding online freedom, but its appeal as an antiestablishment movement has lured many young voters to the ballot boxes, catapulting it into two state parliaments in less than a year.

Polls show the all-volunteer Pirates — who offer little ideology and focus on promoting their flagship policies of near-total transparency and an unrestricted Internet — as the country’s third-strongest political force, leapfrogging over more established parties.

The tremendous success has doubled the Pirates’ membership to 25,000, but it has also handed the party a crucial challenge set to dominate their convention starting Saturday: A party founded as a rebellious upstart must reckon with its new political power and its promise of a voice for all of its members.

As 2,000 members gathered in the northern Germany city Neumuenster to discuss the group’s growth, new polls predicted it would win seats in two more state legislatures in May, with forecasters expecting them to secure about 9 percent of the vote in both states.

"Many vote for the Pirates as a sign of protest. It is not directed against democracy, but it’s based on the unhappiness with the functioning of the established parties," said Alexander Hensel, a political scientist who studies the Pirates at the Goettingen Institute for Democracy Research.

Analysts say that despite the country’s robust economy and low unemployment, many Germans — like others around the world — are disenchanted with the established parties, fueled by outrage over seeing the government bailing out banks and businesses to save the economy from collapsing in the wake of the financial crisis.

Thousands in Germany took to the streets last year in protest rallies supporting the worldwide Occupy movement, but it has now all but fizzled out — with the Pirates appearing to inherit the votes of the disenchanted.

While the mainstream parties in Europe’s biggest economy are struggling to come up with a response to the continent’s debt crisis, the Pirates cheerfully admit that they have no answer to the questions raised by the crisis. Nor do they have a stance on whether German troops should continue to fight in Afghanistan.

But many voters welcome their blunt acknowledgment as a sign of honesty in the political arena. Instead of taking a stand on the pressing issues that more mainstream parties are forced to address, the Pirates demand that public transportation be free of charge and that every citizen be paid a basic income without having to work.

"The Pirates are elected less because of what they stand for than by disappointment with the established parties and for their unconventional methods," Hensel said.

The party’s core pledge of full transparency and participation — live transmission of all meetings and the online involvement of all party members in its decisions, countless Twitter debates and email chains — is reaching the limit of feasibility as the number of party members has mushroomed.

The question is: Will the Pirates change Germany’s political system, or will the system crack the Pirates?

"The party is growing enormously. Integrating all those new members puts the party under great strain in terms of organization. They need to grow proper structures now and have a more professional leadership," Hensel said.

"A party run by volunteers has its limit," he added.

The party’s outgoing managing director Marina Weisband collapsed last week between two television show appearances. She was briefly hospitalized, saying she was just heavily overworked. The 24-year-old has now joined the ranks of some top Pirates who advocate for having professional leaders running the party. Some are also proposing that the party’s leaders should have a greater say in shaping the Pirates’ policies.

But to grassroots Pirates, those calls amount to mutiny.

"The Pirates’ opinion is created by the party members, not dictated by the chairman," party leader Sebastian Nerz said. "The individual’s freedom stands at the top."

Recently, however, the party has been marred by a scandal over to handle the far-right past of some of its members, with many Pirates refusing to exclude anyone from the party in a bid to remain a fully open and inclusive party.

Soon enough, the party will have to have more professional politicians if pollsters are right: In North Rhine-Westphalia, Germany most populous state with 18 million inhabitants, the Pirates can expect to get 9 percent of the vote in mid-May, according to Emnid, which surveyed 1,001 people for Focus magazine this week.

Another poll for public broadcaster ARD published Friday equally found the party to secure about 9 percent of the vote in Schleswig-Hollstein state’s May 7 election.

Pirate parties are now present in several European countries, but only in Germany have they skyrocketed to such success. In Sweden, where the movement originated, the party won 7 percent of the vote in European Parliament elections 2009 but less than 1 percent in national elections the next year, making it a marginal party, albeit with a strong voice on cyber issues.

Germany’s political establishment at first did not take them serious at all. Now that they seem poised to be in four of the country’s 16 state legislatures within a month, politicians can’t ignore them any longer.

"They are an interesting appearance. And we don’t know yet how that will develop," conservative Chancellor Angela Merkel told Saturday’s edition of daily Leipziger Volkszeitung.