Overboard Outboard

Barry Thompson | VOLUME 32, ISSUE 2

Seven Marine builds outboards with serious attitude …

Powerful Serenity is one of the emotive phrases that appears on the website of America’s Seven Marine outboard engine company. While there’s no problem whatsoever about the ‘powerful’ reference, I’m still struggling with ‘serene’. I mean, we’re dealing here with a company that produces the world’s most powerful outboard engine, a stupefyingly outrageous six-litre monster that produces up to 627hp. I’d think ‘extreme’ would be more appropriate.

Seven Marine was founded in 2010 by a team of innovative engineers with decades of experience in the marine industry. Their stated goal was to build the most powerful and technologically advanced, highest-performance outboards on the planet. And there is no question whatsoever that they have achieved what they set out to do – and more.

Mind you they don’t come cheap and, at around US$100,000 (AU$130,000), it will be interesting to see how many turn up on the transoms of boats in Australasia. In the US, they are very popular in quad or triple rig set-ups on large 40 to 50ft sportfishing centre cabin boats and it’s not unheard of to see as many as four across the transom. As the old joke goes: “Why four outboards?” “Because we couldn’t fit five!”

Each engine weighs in excess of 500kg and, in multiple installations, can push boats to speeds of more than 80mph (130km/h).


Headquartered in Germantown, Wisconsin, Seven Marine’s company president is Rick Davis, a former Mercury Marine engineer who was involved in the development of leading power product lines, including Mercury Optimax, Mercury Verado and Cummins-MerCruiser Diesel Zeus inboard pod drives.

The Seven Marine outboard is built around an aluminium, fuel-injected and marinised 6.2lt supercharged Chev-based LSA Gen 4 V8, hooked up to a powerful MEFI 6 engine controller and run on 89 octane fuel. Depending on configuration, its engines are rated at either 557 or 627hp.

Confirming the prowess and innovation of its 627 model, Seven won an Innovation Award for it at the 2016 Miami International Boat Show. While it obviously lacks nothing in power, presentation is a big sales point in the US market – the recently introduced SpectraBlade cowl, which incorporates strips of diffused LED lighting that can produce just about any colour imaginable, has received much attention. Of course, nobody actually needs an outboard with LED lighting, but then again nobody has a Seven (or four) hanging off their transom without wanting to get noticed.


Turn the key and the big engine ignites with a classic V8 growl. Dry chambers bark as the twin water pumps propel water through the dual exhaust in a cascading flow. The overboard, acoustically attenuated exhaust then settles into a rich idle throb.

The 9cm exhaust, combined with traditional thruhub outlets, keeps running decibels to a minimum when cruising. Seven says its exhaust system makes a statement – but without overstating the argument.

A high-performance engine needs high-performance cooling and these feature closed-looped systems, claimed to be the most advanced ever employed on an outboard motor. Keeping them cool is an ethylene glycol mix that continuously flows through the engine in a closed loop. While seawater is pumped through coolant and oil heat exchangers, it never comes into contact with internal engine components, so saltwater corrosion is not an issue.

A ZF Marine transmission, with roots from inboard technologies, is designed exclusively for the V8. Fly-by-wire controls, wet disc clutches, and spiral bevel gears handle the shifting, providing smooth, progressive transfer of power from the engine to the prop, says Seven Marine.

Designed from the start with joystick operation in mind, the computer-controlled transmission can seamlessly shift on command, significantly improving manoeuvrability. Integrated troll control also allows a nearly infinite adjustment of trolling speeds.

Engineering the transfer of power from the horizontal crankshaft configuration – a first for the outboard industry – presented new design opportunities, such as the ability to change a variety of gear ratios for different applications by virtue of easy access to the twin-pinion gearcase. Lightweight helical gears transfer the power from the crankshaft to the gearbox and then onto the props.

A stainless-steel rear bearing carrier offers solid prop shaft support, and a longer strut accommodates up to 18in diameter propellers.

Seven says its outboards push the performance envelope to new levels. When you’ve got up to 32 supercharged cylinders churning out more than 2500hp bolted to the transom, there’s no doubt that envelope is under more than a little strain …