The Edinburgh-based sister companies – headed by former Forth Ports chairman Bill Thomson – disposed of most of their shipping investments to take advantage of high prices in the market.
The companies' main vessel, the Forth Bridge, which had been on charter in the Caribbean, was sold in April 2008 for $7 million.
Forth and Celtic, thought to have some 5m between them in assets, had intended to buy back into the shipping market when prices were lower.
Although the companies said their strategy to exit the market had "proved to be a good decision" as ship values had since plunged, they admitted it had proved difficult to find suitable investments.
"Although we have examined more than a dozen projects and still have one possible investment under appraisal, we have to advise that we have not so far found one which meets our criteria," said Thomson in a letter to shareholders.
"There are vessels for sale, some at historically low prices, but the difficulty is always finding employment at rates which will not only generate a satisfactory return but is provided by a company that we are confident will still be around if the hard times persist."
Thomson said the directors of the two companies had now reconsidered their strategy and believed it would be in the best interests of shareholders to look to return capital to them and was in discussions with its advisers on the best route.
In the meantime, Thomson said the companies were still in a position to buy back shares on the PLUS market where they are traded.
Thomson left Forth Ports as chairman in 2000. He had earlier been linked with a possible 750p-a-share offer for the company.