February 6th 2011. By Lenny Rudow.

Aspen C90: An Asymmetrical Wonder

This unique cruising cat relies on a single diesel and different-sized hulls to achieve high mileage at good speeds.

Aspen Power Catamarans may build the world’s most innovative pocket cruiser, the C90. Hold on a sec—isn’t “innovative” a vastly overused word, when it comes to boats? You bet. Aren’t these claims usually little more than marketing talk and PR gab? Yes. But in this case, the shoe fits.

The C90 is a unique assymetrical powercat.

The C90 is a 28-foot twin-hulled powercat with a full cabin. It can putt along at about seven mph while burning just a hair over a gallon per hour, which translates to nearly seven miles to the gallon. Kick it up to 15 mph, and the boat still gets 3.8 miles to the gallon. Even at wide-open-throttle speeds of almost 22 mph the boat still gets 2.5 mpg. Impossible, you say? That would make it one of the most efficient pocket cruisers in existence! Exactly—and you’ll be stunned at how the C90 attains this performance: it runs on a single 150-hp inboard Cummins diesel, housed in one of the two hulls.

A cat that cruises on one off-center engine? And a relatively tiny engine, for this size boat? Yup. The hulls are asymmetric: the port hull is about 35-percent thinner than the starboard hull. This reduces overall drag by about 50 percent, while at the same time countering the torque created by having an off-center powerplant. As a result, the C90 tracks perfectly straight, while running far more efficiently than either a monohull or a modern twin-engine powercat.

The two hulls are sized differently, but the loads are equal.

To prove the point, let’s look at some numbers. An average monohull in this size range would at best post a cruising efficiency of between 1.7 to 2.0 miles to the gallon at 15 mph. An average powercat in this class, on the other hand, could be expected to get closer to 2.0 to 2.5 miles to the gallon while on a plane. Now remember: the C90 gets close to 4.0 miles to the gallon at 15 mph.

Now I know what you’re thinking: If one hull’s larger than the other, the boat will have a very strange list, or will roll unevenly. Banish the thought, because Aspen’s one-of-a-kind design eliminates this issue. The two hulls are sized differently, yet the waterplane area (the amount of hull that’s submerged beneath the waterline, and therefore displaces water) is perfectly balanced. The hull housing the engine is 35 percent larger than the other hull, and it bears a 35-percent larger load. The net result? Step from port to starboard to shift your weight as quickly as possible, and you can’t tell any difference in effect whether you’re going from port to starboard or vice versa. Rolling in rough seas the hulls remain in balance, and as you load the boat, the two hulls submerge evenly.

More about dealing with rough seas when you’re in the C90: As on most well-designed powercats, impacts are greatly reduced compared to monohulls. The boat rides on a cushion of air compressed between the two hulls, which softens the ride as the extremely narrow hull entries cleave open the waves.

The Aspen C90 galley has a two burner propane stove and oven.

Of course, as with all boat designs, there are trade-offs to consider. Because the power comes from a single, off-center engine, dockside handling would normally be atrocious. Aspen has taken care of the potential problem by fitting its boats with both bow and stern thrusters. With these, the boat can be spun in its own length and easily maneuvered into a slip.

The C90’s innovations don’t end at the waterline. This boat is built with the latest in both green-minded technology and cruising capability. A pair of 80-watt solar panels on the roof feed a pair of group-27 deep-cycle house batteries. The system is controlled via a Solar Boost 2000 automatic charge controller, which ramps down the electrical feed as the batteries come up to a fully charged state. If the controller senses another charge source, like the engine or battery charger, it shuts off its feed entirely. The Nova Cool refrigerator is also the latest in lean and green, with a mere 2.5-amp draw. Between the solar panels and the low-draw reefer, you can spend essentially unlimited time on the hook, and off of dockside power sources.

Since the boat’s long-distance, long-term cruising capabilities are so significant, it’s equipped to be comfortable for the long haul. The galley includes a propane Seaward-Princess oven with a two-burner stovetop. To take full advantage of every iota of space in the boat, a full berth is hidden underneath of the galley. The four-seat dinette provides more sleeping space by converting into a double berth. The Burmese teak-trimmed cabin also has an immensely comfortable Bentley helm seat, with dual-density foam and adjustable armrests. Forward and below, there’s a queen-sized berth, with an enclosed head built into the starboard-side hull, under the passenger’s helm seating.

The hull bottoms are armored to survive heavy impacts.

Go belowdecks to check out all of this stuff, and you immediately wonder how in the world they managed to cram so many goodies into a package that’s so small. Remember—this is a pocket cruiser, just a hair over 28’ long (30’ with the transom step) and just 10’ wide. The secret is, once again, the boat’s dual hull/single powerplant design. The amount of space dedicated to the engineroom is a small fraction of what would be necessary in most straight-inboard boats, since you only need room to house one 150-hp powerplant.

Along with the smaller power is a reduced need for fuel. So the Aspen can open up even more space by utilizing a mere 80-gallon tank. With the awesome efficiency, this still gives you plenty of range (487 miles at 7 mph or 270 miles at 15 mph, with a 10-percent reserve), for which most boats of this size in a twin-screw monohull version would have to haul double the fuel.

If you guessed that such a cutting-edge boat is going to be built with the very latest in fiberglass construction techniques, you’d be right on target. In fact, the Aspen’s put together unlike any other boat. Resins are a mix of vinylester and isophthalic, and fabrics used include both S-glass and Kevlar. Cores are cross-linked PVCs. Stringers are 2.5” molded glass over foam core, reinforced at the motor with 3/8’ steel plates. The bows of the boat are beefed up with three feet of glass-encapsulated Coosa composite surrounded by foam, along with a layer of Kevlar. And the hull bottoms are armored to survive heavy impacts, with double-layer construction consisting of fiberglass backed by two layers of fiberglass-wrapped cross-linked closed-cell foam core. Total thickness of the structure: two inches.

So, does anyone still want to say the Aspen’s claim to innovation is no more than a marketing ploy? That it’s all just PR hype? No? What’s the matter – this cat got your tongue?

For more information, visit the Aspen Power Catamarans website.

Lenny Rudow
With over two decades of experience in marine journalism, Lenny Rudow has contributed to publications including YachtWorld, boats.com, Boating Magazine, Marlin Magazine, Boating World, Saltwater Sportsman, Texas Fish & Game, and many others. Lenny is a graduate of the Westlawn School of Yacht Design, and he has won numerous BWI and OWAA writing awards.