Clash of the Titans Page 2

Clash of the Titans - Metal Construction continued
Clash of the Titans
Part 2: Today’s Aluminum Alloys

By Capt. Bill Pike — September 2001

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Boon's reasoning is persuasive. For one thing, he contends that today's aluminum alloys have higher strength-to-weight ratios than ever before, a development that makes modern aluminum as strong as steel, which is typically thinner but much heavier. The implications here are obvious. Saving weight while maintaining strength in a given vessel means safely getting away with smaller engines and running gear, which in turn cuts fuel consumption and extends range. Such niceties add cruising flexibility to a yacht's repertoire and help amortize the higher initial material costs of aluminum. Boon also contends that reduced structural weight, when coupled with other complex design factors, makes it possible to put the engine room well aft in an all-aluminum yacht rather than amidships, which is the conventional location on steel-hulled boats. Such a move frees up space for amidship fuel and ballast tanks that can be filled or pumped free without negatively affecting trim and stability.

Boon's not alone in his fervor. Phil Friedman, CEO and president of Palmer Johnson Yachts, bolsters the Dutchman's case with some persuasive reasoning of his own. First, Friedman says the higher initial material costs of all-aluminum construction are offset not only by greater running efficiency but also by time and labor savings gained from the comparative ease of handling lightweight aluminum plates in-build as well as  reduced preparation time and material costs--aluminum bilges, for example, need not be flame-blasted, primed, and painted the way steel bilges have to be. Palmer Johnson, states Friedman, can create all-aluminum vessels of less than 70 meters (about 220 feet) that are price-competitive with steel ones. And second, Friedman suggests that putting engines aft and variable ballast tanks amidships may usher in a new era of big-boat performance.

 "With increasing frequency these days, builders are being asked to boost the top speeds of very large vessels, even trideckers," he says. "Central ballast tanks that don't substantially affect trim may be the answer. You build the boat light to begin with. This gives you extraordinary speed in good weather. Then in bad weather you ballast down for stability and run slower."

Of course, not everybody's as keen on aluminum hulls as Boon and Friedman. Steel is undeniably strong, seaworthy, and cost-effective, else it would not continue to be the preferred material for commercial shipbuilding in the world today. Many proponents charge that steel vessels ride better than aluminum ones in a seaway, mostly because they're heavier and so exhibit superior stability. Michael Breman, sales director of Lürssen Yachts in Germany, a builder well-versed in both steel and aluminum construction, supports this last view. However, he challenges established thinking on steel-hulled yachts with aluminum superstructures--the assumption that the composition of such vessels is supposed to cut weight aloft and thereby bolster stability and performance. Breman maintains that building an aluminum superstructure to current classification strictures and MCA safety standards adds so much extra weight in fireproofing insulation and protective steel panels for galleys, pantries, and other critical areas that the weight advantage all but disappears. "Then you're stuck with steel polka dots all over your supposedly lightweight, aluminum superstructure," he adds. Boon heartily disagrees, incidentally, contending that a fluffy, insubstantial material like insulation does not add that much weight.

The final voice in the aluminum-versus-steel controversy comes from the Big Easy, where the drawl is more soothing than Southern. Billy Smith of Trinity Yachts, which last year split off from commercial and military builder Halter Marine, contends there's little difference between aluminum and steel in terms of building expense, strength, or seakindliness. He states that preparing a steel vessel for painting, especially in bilge areas that must be first sand-blasted and flame-sprayed with hot zinc, ultimately renders the construction cost about the same as an aluminum vessel where interior surfaces can be left bright. As far as strength goes, Smith cites the durability of all-aluminum crewboats and the gutsiness of the all-aluminum, ice-class, ABS-certified yachts being offered by Trinity. And finally, Smith flatly dismisses the old saw about steel boats being more stable and seaworthy. Any vessel worth its salt, he says, should be designed to have a certain measure of initial stability or metacentric height, whether it's made of steel or aluminum--or fiberglass, for that matter.

"Which leaves us with weight as the only primary consideration," Smith summarizes. "If you're building a semidisplacement or planing hull, go with aluminum or maybe just an aluminum superstructure to reduce weight. If you're building a full-displacement boat, go with steel."

Smith adds one caveat, however. Yacht buyers with serious globetrotting aspirations should make the choice between aluminum and steel based not on how the material will serve them in stateside and European environs, but on how it will perform in the middle of nowhere. Specifically, he cautions against taking aluminum-hulled motoryachts or even high-tech composite motoryachts into the uncharted waters of Third World countries.

"Hole a steel boat in Bora Bora," he warns, "and you'll likely be able to come up with a welder who can put on a doubler plate. But finding a guy who can patch an aluminum or fancy composite hull? Good luck! Sophisticated welding and composite repair are in short supply in far-out places."

If he weren't in a pretty far-out place himself at the moment, I'm pretty sure my tug-skipper friend would heartily agree.

Lürssen Yachts Phone: (49) 421-6604-166. Fax: (49) 421-6604-170.
Palmer Johnson Yachts Phone: (920) 743-4412. Fax: (920) 743-3381.
Trinity Yachts Phone: (504) 283-4050. Fax: (504) 284-7171.
Vripack Yachting International Phone: (31) 515-436600. Fax: (31) 515-436634.

Next page > Metal Construction Photo Gallery > Page 1, 2, 3

This article originally appeared in the June 2003 issue of Power & Motoryacht magazine.

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