Rated at 557 ponies, 59 percent more power than its closest rival, Seven Marine’s 557 is the world’s most powerful outboard. This brute is based on a supercharged, 6.2-liter, aluminum Cadillac LSA V-8. It’s the only outboard with a closed cooling system, a key anti-corrosion feature.
The horizontal powerhead turns the drivetrain 90 degrees through a ZF Marine electronic transmission, a derivative of the gearbox used in ZF’s pod drives. The 557 can be had with gear ratios ranging from 1.4:1 to 2.1:1.
The beefy, twin-pinion lower unit accommodates propellers up to 18 inches in diameter, ensuring delivery of the engine’s 550 foot-pounds of torque. The 557 also features dual exhaust outlets; at low speeds, exhaust gases exit through ports above water. As speed increases, this transitions to a through-hub exhaust. There are also dual water inlets. The 557’s 150-amp alternator surpasses the output of any other outboard. Integral power-assist steering, co-developed with Latham Marine, helps rein in the torque. The 1,045-pound 557 weighs 282 pounds more than Yamaha’s 763-pound F350 V-8. The 557’s power-to-weight ratio is 0.53 — 15 percent more than that of Yamaha’s and equivalent to Mercury Racing’s Verado 350 SCi. It’s 7 percent lower than that of Evinrude’s E-TEC 300.
Aboard our Midnight Express 39 test boat, triple 557s pulled with exhilarating acceleration and the screaming sound of a jet fighter, peaking at 105 decibels at wide-open throttle. They are louder than other triple outboards in our boat test database. Think “satisfying roar.”
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During factory trials, Seven Marine pushed this 39-footer to 81 mph, a credible number. We ran with a full gas tank and a crew of four. Plus, our test boat’s owner ordered the boat set up for cruising rather than speed. And Seven is in the process of optimizing the engine’s computer mapping.
Triple 557s with joystick steering cost $270,000 for 1,671 hp. You’d need five 350 hp outboards to match it, a power package weighing up to 22 percent more. Five outboards would also require more rigging, and a quintet of gear cases would generate more drag. Yet, you can buy five 350s (without joystick) for between 42 and 45 percent less than the triple 557s’ cost.
Still, Seven Marine’s 557 is an engineering triumph: the world’s most powerful outboard.
