Children play with video games while their parents doze on deck. Teen-agers watch a film in the cinema while truck drivers prop up the bar and day trippers stock up on duty-free cigarettes and alcohol.

With their many leisure facilities and relaxed easy going atmosphere, the dozens of ferries that sail back and forth between Britain and the continent each day give even the most nervous of travelers little cause for alarm.But because so many millions of people use the ferries each year, the Zeebrugge ferry tragedy seemed particularly shocking. It is all too easy to imagine the dreadful scenes on board as the Herald of Free Enterprise capsized just outside the Belgian port. Families were separated; corridors became vertical shafts; chairs, luggage, life jackets, bottles, crockery and cutlery were hurled around as the ship flipped over.

Even though the final death toll of 134 was much lower than at first feared, the disaster will haunt Britain for years to come, if only because of the freak nature of accident.

People who could never be persuaded to fly are quite happy to take a ferry across the English Channel - and some 20 million do each year. Although an element of danger is clearly apparent when journeying by air, and even by road or rail, the ferries seemed, until that fateful day of March 6, quite literally as safe as houses.

While the risk of collision with a giant tanker as the ferries cut across one of the busiest sea lanes in the world might seem a remote possibility, who could possibly feel in danger just a mile out of port and well in sight of the harbor lights on a calm clear evening?

But even as investigations began into the cause of tragedy, ferry services were continuing as normal, and there is little likelihood of more than a temporary dip in passenger traffic as a result of the accident. Certainly commercial traffic will not be affected - for there is no alternative but to ship most freight by sea.

As an island, Britain is faced with only two choices for moving goods in and out of the country - air or sea. And as a major trading nation whose exports account for about one-third of gross domestic product, the U.K.'s overseas trade is absolutely vital. The ferries are the country's lifeline to its most important overseas market.

This was not always so. In fact, Dover, the country's busiest port, only began handling cargo in 1965.

But as the pattern of trade shifted after Britain joined the European Community in 1973, so the east coast ferry ports grew in importance, while the deep-sea ports on the other side of the country started to lose business.

Prior to membership, about 20 percent of Britain's foreign trade was with other members of the Commonwealth (former British colonies such as Australia, New Zealand, Canada and more than 40 other states spread around the world). That proportion has slipped to around 11 percent, while the share of trade with other EC countries has climbed from under 30 percent to more than 50 percent. West Germany equals the United States as Britain's single largest trading partner.

The roll-on roll-off ferries, with their fast turnaround times, carry a very substantial share of cargo shipped between Britain and the continent. There are around 250 ferry services across the English Channel and the North Sea each day to and from dozens of different ports.

But the ferries provide far more than just a commercial link. Unlike the Staten Island ferries that primarily carry commuters to Manhattan, the cross- channel ferries cater for a broad range of passengers. In addition to the truck drivers who regard the short crossing as a welcome break in a journey that might take several days, huge numbers of holiday-makers heading for Mediterranean beaches take their cars across the channel on ferries, English trippers pop over to Calais for the day to stock up on wines and cheeses, while French and Belgian visitors make frequent trips to Britain to shop for clothes and electrical goods - or whatever exchange rates dictate is a good buy.

The ferry that sank was capable of carrying 1,300 passengers and 350 automobiles (or an equivalent of cars, coaches and trucks) on its huge 420- foot-long car deck, while in the summer a new generation of super-ferries with almost twice the vehicle and passenger capacity are scheduled to come into service.

Commercial pressures and worries about competition from the channel tunnel when it is completed in 1993 are forcing ferry owners to operate bigger and faster vessels and cut down the time spent in port. In Dover, the port to which the Herald of Free Enterprise was heading, the turnaround time is down to about an hour.

This factor is bound to come under close scrutiny during investigations into the disaster since the fact that the ship sailed before her bow doors had been closed - a common enough occurence as any regular traveler will testify - clearly contributed to the accident.

Normally these are well above the water but on that Friday something caused the vessel to dip, and once water had poured through the doors into the huge open car deck, the ship became unstable within minutes.

Whether or not the ferry disaster strengthens support for the channel tunnel will not become apparent until the summer when financiers are due to subscribe to a 750 million ($1.2 billion) funding effort. The first share offering last year received a poor response and more enthusiastic support next time might indicate a reappraisal of the tunnel's commercial prospects.

But all that is some way off, and in the meantime the ferries will continue to provide an economic, social and cultural lifeline between Great Britain and the rest of Europe.

Britain's worst-ever peacetime shipping tragedy since the Titanic won't be forgotten, but neither will it be allowed to interfere with the essential part the ferry services play in the day-to-day running of the country.

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