Innovative New Outboards from Seven Marine
I am proud to say I was the first writer to collect test data on the most powerful outboard to date – Seven Marine’s 557. I tested and videotaped a center console – the Midnight Express 39 Open – with three of the 557 hp outboards in the waters off Miami, Florida. Ultimately, I walked away impressed with these innovative engines, which generate 59 percent more power than the closest rival.
Wisconsin-based Seven Marine has taken an entirely new approach to outboard design. At the heart of the 557 lies a supercharged Cadillac LSA engine — a 6.2-liter all-aluminum, multi-point fuel-injected V-8. It also stands as the only outboard with a closed cooling system, which will help immensely in preventing saltwater corrosion.
Instead of perching the engine on end, as with other outboards, Seven Marine mounts it horizontally, like an inboard engine. To turn the drive train 90 degrees, the 557 employs an electronic-shifting ZF Marine transmission — a derivative of the gearbox used in ZF’s pod drives. The engines can be specified with gear ratios ranging from 1.4:1 to 2.1:1. All shifting takes place in this transmission using ZF fly-by-wire controls.
The beefy, yet streamlined, twin-pinion lower unit measures 4.75 inches in diameter and can accommodate the largest-diameter propellers of any outboard — up to 18-inches — to take advantage of the engine’s 550 foot-pounds of torque. The 557 also features dual exhaust outlets; at idle and 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, which can be factory-tuned for different boat types, ranging from high-performance fishing boats to yacht tenders. The 557 boasts a 150-amp alternator – more than doubling that any other outboard.
When equipped with two or more 557 outboards and a bow-thruster, a boat can also employ a joystick-control system to help ease low-speed maneuvering in tight quarters. While the outboards do not turn independently, the electronic shifting and bow-thruster work in unison to let you pivot and walk the boat into a slip.
At speed, integral power-assist hydraulic steering developed in partnership with Latham Marine helps rein in the big outboards. Listed at 1,045 pounds, the 557 weighs 282 pounds more than the next heaviest outboard, Yamaha’s 763-pound F350 V-8. The 557’s power-to-weight ratio is 0.53 – 15 percent greater than that of the Yamaha F350, about the same as Mercury Racing’s Verado 350 SCi and 7 percent lower than Evinrude’s E-TEC 300.
The three 557s purred like kittens at the dock, registering a muffled 69 decibels at idle at the helm. Shifting-noise in the wet-disc clutch ZF tranny was barely perceptible — no clunks or clanks — a nice benefit when using the joystick, which can shift frequently while docking. As the 557s spooled up on acceleration, it reminded me of a jet-fighter aircraft as it begins its roll. To help boost hole shot and minimize slippage, Midnight Express equipped the outboards with Mercury Maximus five-blade propellers, but the wheels still take a few seconds to hook up. Our time to plane and 0 to 30 mph times were both in the mid-seven-second range. We clocked 25 to 50 mph in 9.3 seconds. From 50 mph, the engines keep pulling with exhilarating acceleration and the screaming sound of a jet fighter. Sounds levels at the helm measured 105 decibels at wide-open throttle.
In previous tests with a lightly loaded Midnight Express, Seven Marine engineers pushed the 39-footer to 81 mph. But in our test, we had a full gas tank and four healthy adult males on board. Also Midnight Express, at the boat buyer’s behest, had set up the boat for cruising rather than all-out speed. As a result, we maxed out at 74.4 mph at 5,200 rpm. Redline on the 557 is 5,550 rpm.
With production motors ready to ship, Seven Marine must now convince boaters that having a set of the most powerful outboards is the worth the cost. The purchase price of the triple 557 package with joystick steering is $270,000, bringing the tariff of the Midnight Express 39 Open to $700,000. That’s steep, but it’s also the only way of getting 1,671 hp with three outboards. Quads are the maximum on the 39 Open, but to get that kind of power, you’d need five 350s, a power package than can weigh as much as 22 percent more; five outboards also require a lot more rigging and a quintet of lower units generate substantially more drag than do three. On the other hand, the MSRP of five 350s (without joystick steering) ranges from 42 to 45 percent less than the triple 557s.
But that’s the price you’ll have pay to own the world’s most powerful outboard.