ROME, Jan 19 (Reuters) - Czech investment group KKCG on Monday said it was launching a voluntary offer worth up to 182 million euros ($212 million) to double its stake in Italian yacht maker Ferretti and push for boardroom changes.

KKCG's offer, which values Ferretti at 1.2 billion euros according to Reuters calculations, comes after a string of share purchases by the group's main shareholder, China's Weichai, drove the stock price higher.

KKCG said its bid of 3.50 euros per share, though below the current market price, represented a 21.3% premium over Ferretti's share price on December 11, the last trading day before Weichai started adding to its holding. 

By 1034 GMT Ferretti's Milan-listed shares were 0.4% lower at 3.63 euros each. The company's shares are also traded on the Hong Kong bourse. 

KKCG, which currently owns 14.5% of Ferretti through its KKCG Maritime unit, said it would put forward its own candidates for a new Ferretti board.

Two people close to the matter told Reuters that KKCG's slate of board nominees would not seek to replace the company's current top management.

It added it had no plans to take Ferretti private, targeting a stake of just below the 30% threshold that triggers a mandatory full takeover.

"This offer reflects our ambition to strengthen our long-term investment in Ferretti and contribute to its future growth and development," KKCG founder and chairman Karel Komarek said, adding that his firm would support both internal growth and acquisitions. 

UniCredit acted as lead financial adviser for the offer.

($1 = 0.8604 euros)

(Reporting by Giulia Segreti, Valentina Za and Elisa Anzolin; Editing by Thomas Derpinghaus, Kirsten Donovan)