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Cutting a Wide SWATH

David Schneider

Unlike passenger liners or oil tankers, scientific research vessels are rarely behemoths. The average length of the ships in the University–National Oceanographic Laboratory System (essentially the U.S. academic research fleet) is, for example, just 51 meters. The rolling and pitching of such small ships, which stay at sea for many weeks at a stretch, can bring on a debilitating mal de mer. And the rocking motion makes it difficult for queasy scientists to deploy delicate instruments, which can easily smash against the side of the heaving vessel as they are lowered into the sea.

One solution is to use bigger—and thus steadier—ships. But taking the QE II out for routine oceanographic surveys would be rather expensive. So scientists at a number of research institutes are now pursuing a different course. They are opting for ships of a variety that was pioneered more than two decades ago, known as Small Waterplane Area Twin Hull, or SWATH for short.

Western Flyer . . .Click to Enlarge Image

SWATH ships have two pontoon-like hulls, which are connected to vertical struts that support the central decks and compartments. Unlike pontoon boats, the two hulls of a SWATH ride under the waves. In a sense, the twin hulls resemble two shallowly submerged submarines. And like submarines cruising under the surface, they do not feel the effects of the waves crashing above them, giving rise to a notably smooth ride even in rough conditions.

"Sometimes you can be going 15 knots, and you feel like you can play pool," says Larry Mayer, a marine geologist at the University of New Hampshire, who has often worked aboard the Frederick G. Creed, a 20-meter SWATH survey vessel of the Canadian Coast Guard.

The Creed was named for a naval architect who began promoting ships of this type in the 1930s. But it was not until 1968 that the first vessel of this design was built in the Netherlands. The greatest strides in advancing this technology came in the following decade, when the U.S. Navy constructed a 27-meter SWATH vessel for testing and demonstration. Named the Kaimalino (Hawaiian for "calm waters"), it served admirably. In particular, Navy engineers were able to investigate the stresses imposed on the structure and use this information to design bigger SWATH vessels, ones intended to make work more bearable for crews patrolling storm-tossed northern seas for Russian submarines.

Built in the 1990s, these Navy surveillance ships (a class that is known by a military acronym, T-AGOS-19) achieved their aim. At the same time, quite a few similar vessels entered service for a variety of other purposes. The 50 or so SWATHs now plying the world's waters provide everything from comfortable dinner cruises in Hawaii to smooth ferry rides across the stormy Irish Sea. And two SWATHs now sail just for scientific research: the 62-meter Kaiyo of the Japan Marine Science and Technology Center and the 36-meter Western Flyer of Monterey Bay Aquarium Research Institute (MBARI). Two more are on the drawing boards and will soon put to sea for the Woods Hole Oceanographic Institution and the University of Hawaii.

Although the prospect of conducting research from a stable ship is inviting, some seagoing scientists have expressed reservations about SWATHs—about their deep drafts, their limited ranges and particularly about the seaworthiness of these vessels. Robin Bell, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory, says, "I wouldn't be too thrilled about taking one out on Georges Bank," alluding to some notably treacherous shallows east of Massachusetts (and not far from the sinking of the Andrea Gail, the doomed fishing vessel documented in Sebastian Junger's The Perfect Storm). And the experience of MBARI's Western Flyer does little to calm such concerns.

This SWATH research vessel entered service in 1996, and serious problems immediately became obvious. During one of its early cruises, half-meter-long cracks opened up on the transom, less than two meters above the waterline. With this not-so-subtle hint that something serious was amiss, the crew looked harder and soon discovered more cracks in the framing of the vessel and in various watertight bulkheads.

The Glosten Associates, a firm of naval architects retained to study these problems, recommended that operation of the Western Flyer be severely restricted. They indicated, for example, that it should not be subjected to waves larger than a meter or so in height coming at it from the side. The vessel was taken completely out of service in 1998 so that a comprehensive strengthening of the structure could be done. Bruce Hutchison, Glosten's senior vice president for ocean engineering and analysis, acknowledges the immense scope of that task, which required taking the skin off the vessel and dismantling much of it: "In truth, one could have built a new SWATH for what it cost to fix."

Giving a twin-hulled ship enough strength to resist Neptune's fury is indeed no small feat. Al Dinsenbacher, who once headed the Navy's research and development for the structural aspects of SWATH design, explains it simply: The ocean is "trying to take those thin little struts and bend them right off the upper box." Dinsenbacher reports that even the well-regarded T-AGOS-19 ships sometimes experienced some minor cracking. And he notes that Japan's research SWATH, the Kaiyo, may have required some later hull strengthening. Part of the problem, he says, is the very steadiness of these ships: "With SWATHs in a beam sea, it feels great. So there's no tactile sensation that tells you you're really working the structure."

Designers of Woods Hole Oceanographic Institution's anticipated SWATH vessel are well aware that having too smooth a ride can sometimes be dangerously lulling. So they will be outfitting the new ship with a system that can gauge the stress on the hull and display the results on the bridge. The team, which includes members from the Oceanographic Institution itself, from The Glosten Associates and from Blue Sea Corporation of Houston, are confident that the future SWATH vessel will be able to navigate stormy New England waters better than a much larger monohull. But Robertson Dinsmore, a naval engineer at Woods Hole, says that one problem remains vexing and may account for the reticence of some sea captains at his institution to welcome SWATHs: "They are probably the ugliest ships afloat."

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