An Experienced Catamaran Designer Proves Asymmetry Is More Efficient

Would you like to cruise a 28-footer at 17 mph while getting twice the fuel economy of boats that are a similar weight and size? Maybe you'd prefer to get three times the economy?

That may sound like a pipedream, but manufacturers will continue to chase large gains in fuel efficiency if we're going to continue cruising and fishing many miles from the dock without astronomical cost increases in the future. Well, the future is here now, in the Aspen L80 Launch.

Aspen's L80 Launch boasts a design that I'll wager we'll see copied time and time again, especially if fuel prices continue to rise. It's a powercat with a single 110-horsepower diesel living in the starboard hull. Yup, just one side of the boat has power.

And if you think 110 horsepower sounds downright puny for a 28-foot boat, you're right on target – if this was a conventional design. But the Aspen is radically different. The port hull is about 35 percent thinner than the starboard hull, and the hulls are asymmetric. This reduces overall drag by about 50 percent, while countering the torque created by having an off-center powerplant.

Net result: the boat tracks straight, even when you take your hands off the wheel. And it runs a heck of a lot more efficiently than either a monohull or a modern powercat. It does sacrifice speed and maneuverability can be tough – at least without the standard bow and stern thrusters. But with a base price of $89,000 the Aspen is likely to attract many families who want to get on the water and save money doing it.

DARING TO BE DIFFERENT

Won't the boat list, if one hull is larger then the other? No. The larger hull is the one housing the engine and thus bears a larger load. When all factors are accounted, the waterplane areas – the amount of hull that's actually submerged and displaces water – of the two hulls are identical. The larger hull has 35 percent more load and 35 percent more displacement, and the finer hull has 35 percent less load and less displacement. Step from port to starboard and shift your weight as quickly as possible, and you can't tell any difference.

Now couple the reduced drag of a narrower hull with less waterplane area and a single set of running gear attached to a small powerplant and you get a boat that cruises in the low 20s and tops out in the mid 20s. At 22 mph, the Aspen gets 4.7 mpg. Shave a hair off the throttles and set your course while cruising at 17 mph, and you'll net more than 6.5 mpg. Drop it back even further to a 11.7-mph cruise, and you break 7 mpg. At 7.5 mph, it reaches 8.5 mpg. That means that at trawler-like speeds, your overall range can stretch far beyond normal for a boat of this size.

Compare these performance figures to those of an average monohull in this size range, which would commonly be powered by a pair of 150- to 200-horsepower four-stroke outboards. It would reach a maximum planing speed efficiency of about 1.5 to 2 mpg and a pre-planing efficiency of about 2.5 to 3.0 mpg. Even an average powercat in this class would only get between 2 and 2.5 mpg on plane and 2.5 to 3 mpg at displacement.

Now, in a perfect world, we'd be comparing fuel-burn rates for single-screw inboards, but in the current marketplace, there simply aren't many 28-foot open-deck production fiberglass boats that run with straight inboards. One exception is Shamrock's 270 Open, a center console that houses a 315-horsepower Yanmar below decks. Cruising at about 22 mph, this boat burns around 6 gph, for 3.7 mpg. That's notably better then an outboard-powered boat, but still nowhere near the efficiency of the Aspen – and with a fraction of the deck space.

LOW SPEED PERFORMANCE

Of course, there' a downside to the Aspen's design: It's not exactly zippy. But in the current economy and with fuel prices as volatile as they've been, many boaters may be willing to make a sacrifice in this regard. After all, just 10 or 15 years ago, a 22-mph cruise was considered average. Those who can get back to that mindset can save one heck of a lot of fuel – and cash.

Along with these performance benefits, the Aspen's unusual design provides the usual powercat advantages: a fuller beam from stem to stern, boosting overall deck space; an incredibly smooth ride, with the twin hulls cutting instead of banging through the seas; and increased stability.

Unlike most powercats, however, when you turn the boat, you won't feel like an egg sliding off the griddle. When I tested the Aspen in Biscayne Bay, Florida, I was surprised it handled more like a monohull than a multihull. But, there's a downside to this, too: Since the boat's an inboard, maneuverability is greatly reduced, particularly at slow, dock-side speeds. In fact, it was fairly tricky to slide the Aspen back into its slip at the Marriott Marina – without the four-inch bow thruster and 24-volt Lenco stern thrusters, that is. Apply some sideways power with these, and naturally, maneuvering is a piece of cake. Good thing Aspen includes the thrusters as standard equipment on every boat it builds.

CONSTRUCTION JUNCTION

The Aspen features a fairly techy construction, including vinylester and isophthalic fiberglass resin, S-glass and Kevlar fabrics, and cross-linked PVC cores. The mix of composites is designed to provide the boat with maximum strength at minimal weight, resulting in the L80 tipping the scales at 6,200 pounds (dry). Sure, that sounds pretty hefty for a 28, but remember that powercats usually do outweigh monohulls because there's more surface area, and thus more raw fiberglass, in them. Note, for example, that Glacier Bay's 279 has more than a foot less beam yet weighs in at nearly 5,800 pounds, and World Cat's 290 EC has six inches less beam and tips the scales at 5,700 pounds. Compare that to monohulls like Scout's 282 Sportfish, which comes in at 5,100 pounds, or Sailfish's 2860, at 5,050 pounds.

The 2.5-inch-thick stringers are constructed of foam-cored fiberglass, with 3/8-inch steel reinforcements at the motor mounts. The fuel tanks are beefy, too, and are constructed of 1/4-inch-thick aluminum. Same goes for the stainless steel seat and backrest frames and supports. The standard decking is glass, but you can opt for the synthetic teak on our test boat (which will set you back another $2,800). Another example of prime construction is the windshield, which is tempered glass instead of the more common and easily scratched Lexan or Plexiglas.

The sturdy approach extends to the seating, too, though it may turn off some boaters because it doesn't look slick. While some may prefer molded-in seating for a less-old-fashioned appearance, that would be less functional and less versatile, since it wouldn't be easily removable. Function should definitely come before form, if you ever intend on actually casting off the lines and taking your boat away from the dock.

Torsional force from motor thrust (A) minus torsional force of asymmetric hulls (B) equals straight tracking at all speeds (C).

And the seating is actually one of the strongest assets of the L80. The "Launch" in the L80's name is appropriate, as this boat makes a great one, with seating for up to a dozen people. A low-profile, stainless steel grab rail runs along each gunwale, so everyone has a solid handhold. If you fold out the transom bench seat, you'll pick up seating for two more.

Other highlights: If your crew needs to make a pit stop, they can step down into the lit and vented head enclosure on the port side, equipped with a Porta-Potti. For entertainment, the L80 comes standard with a 200-watt, six-speaker stereo system. Helm chairs for the captain and a passenger are comfortable, padded-arm Pompanettes, and the port-side console is fairly compact. This maximizes deck space, but it also means there's not a heck of a lot of room for electronics. Aspen does offer a factory-installed electronics package including a Garmin 4208 color chartplotter/fishfinder and an Icom VHF, but if you want additional electronics or a screen larger than the 4208's 8.4-inch-diagonal, you'll be hard-pressed to find room at the dash. Of course, for many mariners, this won't be a big deal. But when I stood at the helm, naturally looking at the console with my fisherman's LCD-loving eyes, I wanted more space.

DESIGN INSPIRATION

Where did the idea for such an unusual boat come from? The Aspen L80 is the brainchild of Larry Graf, formerly of Glacier Bay powercats. Graf's powercat designs have won a stockpile of awards, ranging from NMMA Innovation awards to Australia Marine awards. The latest is a 2009 NMMA Innovation Award, for the Aspen design, as the most innovative new powerboat measuring more than 26 feet in length.

In fact the L80 Launch is something of a "mistake," to use the word loosely. Graf started by designing a 39-foot, single-engine cruising cat, powered by a 380-horsepower Cummins diesel inboard. The 28-foot version was originally built as a 2/3 scale model of the 39-footer to prove the concept would work. But as soon as Aspen splashed the prototype, it encountered an unexpected problem: The 28-foot boat proved incredibly popular. After the debut of the L80 and the capture of that Innovation Award at the Miami International Boat Show, Aspen began work on fishing (F80) and cruising (C80) models. It currently offers all three as well as the 39-foot (C130) version of the design and a 48-foot (C150) version as well.

What will come next? Graf hints at extending the L80 by two feet, enlarging the aft deck, and boosting the powerplant up to 150 horsepower. Beyond that, he's not giving anything away. But one thing is for sure: if you want futuristic fuel economy, the Aspen L80 can provide it – today.

Lenny Rudow was senior technical editor for Boating magazine for more than 10 years, and is currently the electronics editor for Marlin and GoBoating magazines.

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