The stake will see Gamesa and BARD jointly marketing and developing offshore services and products. There is also a possibility that Gamesa will manufacture BARD wind turbines under license.
Negotiations on the deal are set to run until March.
Previously Gamesa has experimented with the idea of adapting its 4.5MW machine for offshore usage.
The deal with BARD marks a major change in Gamesa’s reluctance to take the plunge offshore. In 2007, the company pulled out of an offshore wind development joint venture, Ceowind, then describing the offshore segment as a mere "niche".
More recently, insiders have expressed surprise at Gamesa’s exclusion from an offshore R&D project to develop floating turbine technology for deep waters led by Iberdrola Renovables, the world’s top wind operator and Gamesa’s biggest client and shareholder.
Instead, the turbine manufacturing partner in the project is competitor Ecotècnia, acquired by France’s Alstom in 2007.
Jorge Calvet, Gamesa chairmain, said: "Working together, Gamesa and BARD will become leading players in the world's offshore wind power market, by combining BARD's technology and leading position in the German market with Gamesa's industrial, financial and marketing muscle in the three markets that have most potential in the future, namely Europe, the USA and Asia."
BARD managing director Heiko Ross said: "BARD welcomes the strong interest from Gamesa and believes that the envisaged collaboration provides great opportunities for the future growth of both parties."
See 'Analysis - Gamesa moves into offshore with BARD stake' for more
