Irish-American inventor Herbert Williams has unexpectedly resigned from the board of Irish tidal energy group OpenHydro.

This follows the disclosure that in 1987 he was criminally convicted relating to the design and construction of a 92-foot semi-submersible catamaran for Colombian cocaine dealers, according to a report on Newstalk 106 yesterday.

Williams spent 4½ years in federal prison after he plead guilty to conspiracy charges in the District Court for the Southern District of Florida.

In a statement, OpenHydro said: "Herbert Williams tendered his resignation to the board of OpenHydro Group in April 2007, which was accepted, following disclosure to the board that he had a criminal conviction dating back to the 1980s."

OpenHydro, which is chaired by businessmen Brendan Gilmore, has informed all stakeholders of this decision, it said.

"Herbert was unaware of the vessel's purpose at the time of taking the commission and it was impounded by US authorities prior to ever being used. Herbert pleaded guilty to conspiracy and received a custodial sentence," the company continued.

"While disappointing for all, this event will not impact OpenHydro's business," it continued.

A former Alaska fishing trawler designer, Williams patented OpenHydro's unique tidal energy technology in the early 1990s. Its turbines are currently being tested at the European Marine Energy Centre in Orkney, Scotland.

Along with Mr Gilmore, OpenHydro's other high-profile directors include Philip Lynch, chief executive of investment Group One51, and Prof Gerry Byrne, dean of engineering at UCD. It has raised about €12.5 million in over the past two years.