Shipowners whose vessels are not inspected for structural seaworthiness on time will be penalized under new rules approved by the world's top classification societies.

Starting next year, a ship's classification will be suspended if a special survey, due every five years, is not completed or under way by the expiration date on its existing certificate.Classification societies now allow some leeway, but this flexibility will end Jan. 1, 1996, the International Association of Classification Societies said. A three-month extension may be allowed in exceptional circumstances.

The societies announced plans to tighten up the survey rules in June, but released further details last week.

A ship without classification would be automatically detained in many countries and also would not be able to obtain business from reputable charterers or obtain insurance cover.

Classification also will be suspended if a ship's annual survey is not completed within three months of the due date, the 11 members of IACS decided at their June council meeting.

The societies, which together classify around 90 percent of world tonnage, also agreed to give flag states, port states and insurers greater access to ship data compiled by inspectors.

"Information is the key to the exposure of substandard shipping and linked penalties to enforce upgrade - or prevention of further trading - are key to its progressive elimination from the world fleet," said James Bell, IACS permanent secretary.

The societies will accelerate a seven-point action program so that all the initiatives are fully implemented by the beginning of next year. These include tighter rules on the transfer of classification from one society to another and stricter standards for the employment, qualification and training of surveyors. A number of other proposals will be discussed at IACS' next council meeting in December.