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Seven Marine 557 Seven Marine 557
Over two years ago a group of engineers in Wisconsin announced that they were making a 557-hp outboard engine. Prototypes were displayed in February 2011 at the Miami Boat Show. The following Fort Lauderdale show, two operating engines were shown on a 37’ Intrepid, and then engines were demonstrated at subsequent shows with a single on a 30’ Sea Hunter, and twins on a 38’ Fountain. And now, this week at the Ft. Lauderdale Boat Show, no fewer than six boats – 4 with twins, 2 with triples – will be at the dock ready for public scrutiny powered by Seven Marine 557-hp engines. The new Seven Marine 557 is the most powerful outboard engine on the planet.

Seven Marine 557 (Outboard) Specifications
Horsepower 557-hp
Number of Cylinders 8 Cylinders
Configuration V-drive
Weight (lbs/kg) 1,045.00 lbs / 474.00 kg
Fuel Delivery Fuel Injected
Displacement (cu/cc) 376.00 cu / 6,161.54 cc
Shaft Length Options 20'' (508 mm), 25'' (635 mm), 30'' (762 mm)
Shift/Throttle Control Electronic
Steering Control Power Assist
Recommended Fuel 87 octane
Alternator Output 12V 150A

Seven Marine 557 Captain's Report

Seven Marine 557-HP Outboard
Taking a page from the playbook of Apple and the Steve Jobs' notion that the inside should look as good as the outside, Seven Marine has created an arresting look both outside and in.

The Raison d'etre of Seven Marine

Many consumers want to go faster in their existing boats and simply need more horsepower on the limited real estate of their outboard transom. Still other consumers want more interior room in their boats without having to jump up 6’ or so and pay the geometric increase in boat price. Getting engines out of the middle of the boat is one solution.

Seven Marine 557-HP Outboard
The General Motors aluminum block V-8 6.2 L supercharged engine develops 556-hp as installed in the 2014 Cadillac CTS V Sedan. The automaker says that the Cadillac will go from 0-to-60 mph in 3.9 seconds.

The Seven Marine 557-HP Outboard

The Concept of the 557 is to mate the supercharged GM 6.2 L V-8 aluminum block engine with an inboard pod drive-style transmission linked to a rugged “twin pinion” gear case. By linking these three major components Seven Marine has harnessed prodigious horsepower and directed it through a rugged drivetrain.

A single 557-hp engine could replace two conventional outboard motors, thereby saving weight, reducing lower-unit drag, and reducing the total number of parts in the propulsion system. The result should be a more rugged, more efficient propulsion system.

Seven Marine 557-HP Outboard
This picture shows the fly wheel end of the GM engine. Attached to it is the crucial ZF transmission that harnesses the torque and re-directs it below. Seven Marine 557-HP Outboard
The ZF transmission not only harnesses the power from the horizontal engine and re-directs it to a vertical drive shaft, but it also changes gears from forward to reverse and makes the first RPM reduction. "A" indicates the direction of the vertical drive shaft to the twin pinion gear case below.

Increased Transmission Reliability. By taking advantage of the new inboard pod style transmission architechture on the market made for high-torque diesel engines and designing it for an outboard motor, the new 557-hp outboard has an exceedingly robust upper drive train. In the process, by using the ZF transmission, Seven Marine outboard has achieved smooth shifting, slow trolling speed control, and no “clunk” when going in and out of gear, among other things.

Seven Marine 557-HP Outboard
This is the torpedo of the 557 with twin pinion lower unit gearing of the Seven Marine which is exponentially stronger than a single pinion gear, according to Seven Marine. These gears are the key to handling the tremendous torque generated by the supercharged engine as well as to withstand the shock loadings encountered when the prop re-enters the water after catching air.

Seven Marine 557-HP Outboard
Traditionally, outboard drive shafts are relatively thin to keep the width of the outboard leg as narrow as possible to reduce drag. All conventional outboard motors on the market use a single pinion gear in the torpedo gear case also to reduce drag, but at the same time creating the most vulnerable weak point in traditional outboards' drive train. Seven Marine has designed robust drive shafts and twin pinion gears to maximize durability and reliability.

Increasing Gear Case Reliability. By using robust shafts, bearings and a twin-pinion gear design in the torpedo, Seven Marine is taking aboard the lessons learned over the last 40 years in offshore racing with reliable sterndrive and gear case architecture. By removing the directional shifting of gears done in the gear case as is typically done in all outboard engines and moving it to the transmission, Seven Marine has removed yet another problematic area of traditional outboard propulsion systems.

Seven Marine 557-HP Outboard
The 557 is the only outboard engine on the market with its own closed-loop engine cooling system. The above cooling transfer is made by Alfa Laval, a world leader in this technology.

Seven Marine 557-HP Outboard
With the cowling lifted the first thing visible is the Seven Marine closed-loop cooling system – the only outboard in the world that doesn’t run raw water through its block. Custom Marine's polished ss headers can be seen at right. At the bottom of the photo is the Latham Marine hydraulic steering system.

Seven Marine’s Venders/Suppliers

Perhaps the most important aspect of the 557 outboard is that its major components have already been proven by some of the world's leading companies. For example:

  • The 6.2 L supercharged V8 engine is from General Motors,
  • The transmissions are from ZF (a world leader in marine and automotive drive train equipment),
  • The cooling system is built to Seven Marine specifications by a world leader in the coolant systems and fluid handling segment, Alfa Laval,
  • The hydraulic steering system is from Latham Marine (the world leader in steering systems for offshore racing boats),

  • Seven Marine 557-HP Outboard
    The beautiful polished stainless steel headers not only look good, but they carefully direct exhaust gases below with a minimum of back pressure.

  • Exhaust headers are made by Custom Marine (a leading, race-proven supplier of high-quality stainless steel products),
  • SS props are made by Hering Performance Propellers (for over 40 years they have been a major supplier for offshore race boats and high-speed recreational boats)

Numerous other parts such as gear case housings, pinion gears, drive shafts, casings and other components are mostly made by American suppliers including many foundries and machine shops in Wisconsin. Most of these companies have been or are still currently venders to many engine and equipment OEMs in Wisconsin – companies such as Kohler, Harley-Davidson, Briggs & Stratton, Twin Disc – in addition to other marine engine manufacturers.

Synergistic Bonanza. The result of this plethora of resources is that literally a world of talent and expertise, machine tools and infrastructure, has been utilized by Seven Marine’s founders to create the world's most powerful outboard.

People Putting it All Together

The 557 is the brain child of 30-something engineer Eric Davis. His father happens to be none other than Richard (Rick) Davis, who – until he retired in 2008 – was the Chief Technical Officer for Mercury Marine and the man involved with three of the engine company’s most brilliant accomplishments during the last decade – Mercury’s OptiMax 2-stroke direct injection technology, overseeing the development of the Verado program, and bringing the Mercury Zeus pod drive to fruition in cooperation with Cummins Engines.

More Engineers. The third engineer in the family is Brian Davis, who is also in his 30s and heads up international sales, investor relations and finance. A third V.P. and key player is a die-hard fisherman and avid user of offshore boats, Sandy Ballou who is head of domestic sales, which means that he works with both the boat builders installing the engines, as well as customers considering repowers.

Seven Marine 557-HP Outboard
Seven Marine has patented its architecture of an automotive engine used in a horizontal position.

The Power-To-Weight Advantage It is not the scope of this explanation of Seven Marine's outboard to get into the details of the company’s product, which will be done in a later report. However, the most important element of this revolutionary outboard is obviously its power-to-weight ratio.

Supercharging is Key. The basic advantage of the Seven Marine outboard is the fact that its 6.2 L V8 aluminum engine is supercharged which gives the 1,045-lb. (475 kgs.) unit the 557 horsepower. That means that the outboard delivers 1 horsepower for every 1.876 lbs. (.852 kgs.) of package weight (dry).

It also gives it lots of low-end and mid-range torque for fast acceleration.

Seven Marine 557-HP Outboard
The Seven Marine outboard was designed for boaters who want to go fast, have the latest technology, and want more room in their boat for other activities.


We have not tested Seven Marine engines and so will have to reserve comment on speed, fuel consumption, noise levels and handling characteristics until we do. Obviously this package has some built-in benefits such as ultra smooth shifting and high low-end and mid-range torque because of its supercharger. We look forward to testing this remarkable engine.

Seven Marine 557-HP Outboard
The Intrepid 37 was the first boat that the twin 557-hp Seven Marine outboards were tested on. Intrepid president Ken Clinton, whose boats have more hours on the engines than any other, says the new engines are “a game changer.”

Specific Applications for the Seven Marine Outboards

So far we have seen the Seven Marine outboards placed on center consoles for luxury boating, offshore fishing and government patrol work. For example, at the Ft Lauderdale Boat Show this year they will be on six boats including 2 high performance fishing boats, 2 40+ ft luxury center consoles, a 40 ft. RHIB, and a 45 ft. fishing Catamaran. But we think that is only the beginning of the applications for the 557 because these boats were already designed and built for significant horsepower and weight.

In the future, we might see boats designed and built around these engines in other categories such as express cruisers, express fishboats, high-performance go-fast boats, patrol boats of all types and possibly even some large pontoon boats. In addition, this high-powered outboard concept has some geographic implications.

Not surprisingly there is a lot of interest in the Persian Gulf for both high-speed fishing boats and patrol boats and Seven Marine’s first distributor has been signed there to handle local sales and service. High-speed river boats is another application.

Seven Marine 557-HP Outboard
This large center console Midnight Express is powered by triple Seven marine engines and appears to be destined for government work.

Seven Marine 557-HP Outboard
The Intrepid 37 was the first boat extensively tested with twin 557s.

Seven Marine 557-HP Outboard
Yellowfin 36’ center console with twin 557s.

The Price

All of this horsepower, the heavy-duty components, state-of-the-art systems, brilliant engineering, complicated assembly, beautiful exterior with polyurethane paint and graphics, polished ss headers, customization and individual customer consultation does not come cheap. The Seven Marine 557 rig will run twice the cost of horsepower delivered by the production outboard companies. In some cases it may even be nearly three times as much as conventional outboards, according to company spokesman Brian Davis. However, Brian is quick to point out that similar features can only be found in Diesel Pod Drives, which cost 25% to 30% more.

Twin 557s with joystick control and a sophisticated LCD screen have an MSRP of $185,000, for the pair.

Seven Marine 557-HP Outboard
Each Seven Marine is made to order and for that reason the color of the DuPont polyurethane paint and the design can be customized to the owner’s spec. Perhaps these engines will raise dolphin.