The Sea-Gem: a 100mph Air-Cushion Ship by 1963 (Mar, 1962)

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The Sea-Gem: a 100mph Air-Cushion Ship by 1963


NON-ELECTION year 1963 may nevertheless bring a spectacular inauguration.

Some time next year, America’s first air-cushion ship, the Sea-GEM (for sea-going ground effect machine) may streak New York to London on her maiden “flight.”

Riding 3 to 6 ft. above the waves on a frictionless cushion of air, the giant 100-ton craft will be propelled at better than 100 mph by four jet-prop pusher-type engines.

Part ship, part plane, and wholly revolutionary, the Sea-GEM promises its 100 first-flight passengers some surprises.

Your seat-belt cinched, you’ll scarcely notice when the aluminum and stainless steel craft makes the transition from land to water. Though you’ll be “airborne,” the ocean will be but a yard or two below you. Between you and the sea will lie nothing but air—a low-pressure air cushion churned into being by the Sea-GEIV^ dual horizontal fans. “Afloat” but almost “flying,” you’ll feel no sea-sensation, no roll or pitch. Nor will the thundering jet engines (a total 22,000 hp) be audible through the aircraft-like hull. Thirty super-smooth hours after leaving New York, you’ll “land”—actually, slide up a ramp—in London.

The figment of a naval architect’s imagination?

Not at all. The U.S. Maritime Administration announced recently that it’s negotiating a $370,000 Sea-GEM design-study contract with Vehicle Research Corp., Pasadena, Calif., and its subcontractor (and probable Sea-GEM builder), big Douglas Aircraft Co.

The Maritime Administration’s admitted goal: to launch the craft by 1963.

“We’ve been at work on the project for some time now,” confirms Dr. Scott Rethorst, Vehicle Research’s president and one of our country’s foremost aerodynamicists.

The first Sea-GEM probably will be the 100-ton model, but Douglas Aircraft’s president, Donald W. Douglas Jr., recently indicated there is almost no size limit. He pegged as “most efficient,” sea-skimmer ships in the 500- to 1000-ton class.

The Sea-GEM, although using the same air-cushion principle (see page 73, June ’60 S&M), will resemble neither Britain’s now abuilding 25-ton SRN-2 (which is powered by four turbine engines) or several U.S.-sponsored GEM-vehicles, including the now-declassified Avro craft. Pentagon insiders say the Avro failed, in wind-tunnel tests, to meet military altitude specs.

In contrast to the Avro, the Sea-GEM will, at most, skim the water, its great weight supported by the cushion of air (only about 1/4 psi, or 36 lbs. per square foot). Douglas estimates that even a 500-ton craft would operate about half of the time at just 3 ft. or less above the surface—closer in calm seas; higher, and probably slower, when it’s rough.

For its main propulsion, the craft will depend on its four jet pusher engines. But propulsive power, even for the 500-ton ship envisioned by Douglas, won’t need to be anywhere near as big as for either jet planes or helicopters. Reason: The jet engines’ total power is translated into thrust; none of it (as in aircraft) is squandered on lift.

Artist’s drawings of the first 500-ton craft confirm Donald Douglas’s statement that “the craft’s configuration will tend toward a low, functional profile with essentially straight-line elements which permit the structure, although aircraft type, to be simple and low in cost.”

Although the Maritime Administration’s underwriting of the first Sea-GEM ostensibly aims at faster, more economical over-water transport, the Navy is also eyeing the craft as a multi-functioned amphibian: a land-to-water assault and supply ship.

  1. MrSatyre says: December 2, 20101:27 pm

    Interesting. I wonder whatever became of it? When I Google “Sea-GEM”, I come up with a British off-shore drilling rig of the same name, erected around the same time, but also collapsed in ’65.

  2. Christoph says: December 2, 20101:55 pm

    Why would anyone want to do NY-London at 100 mph? Even then you could go way faster by plane. Sounds like a total and utter dud right from the start.

  3. Mason Dixon says: December 2, 20104:03 pm

    Actually the Russians were raising these things to a fine art – google “erkanoplan” – or “Caspian Sea Monster” if you want to see the biggest yet flown – they had them over 300mph. Among the advantages are being able to bigger/more things than one can fit in an airplane at significantly higher speeds than a ship.

    A good Wikipedia entry is here:…

  4. Mason Dixon says: December 2, 20104:13 pm

    Here is an excellent site that shows the “Lun” a Soviet missile launching version – lots of photos that give you a good idea of the enormous size of this thing, and the obvious military applications.…

  5. jayessell says: December 2, 20108:25 pm

    For them to predict it ONE YEAR in the future wouldn’t it have had
    to be under construction when the article was written?

  6. Stephen says: December 3, 20106:16 am

    The nearest approach to this seems to have been the SR.N4 (see link). That had a maximum speed of 70 knots. It was, however, a very different creature, used as a ferry over twenty miles instead of as an ocean liner over three thousand. Hovercraft use a lot of fuel, and because they sink if their engines stop over water, they have to be maintained to a very high standard and packed with backups like an aircraft. The result of the SeaGEM project would have been a machine which was as expensive to build and run as a plane, but not much faster than a ship. It’s hard to see who would have wanted to use it.

    The ekranoplan, referred to above, is a somewhat different technology where lift is provided by wings instead of downward-pointing air jets. It operates at higher speed and can land on water, so it is superior in some ways to the hovercraft. It is surprising that nobody is operating them yet.

  7. LightningRose says: December 3, 20109:37 am

    Stephen, there’s absolutely no reason why a hovercraft (aka Air Cushion Vehicle) has to sink when it loses lift over water. Commercial hovercraft have, in fact, been used on the English Channel for over 40 years.

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