Seven Marine’s V-8 Outboard

Seven Marine's 557 attacks outboard design.

March 15, 2012

Seven Marine 557

Though Seven Marine debuted its vaunted 557 V-8 outboard in February 2011, we’ve had to wait more than a year to actually run one – a single pre-production engine on a Sea Hunter 29 ( center console with a T-top. We estimated the boat weight at around 10,000 pounds (with the outboard).

By way of background, Wisconsin-based Seven Marine ( is attacking outboard design with new concept using a Cadillac supercharged LSA aluminum V-8, mounted longitudinally. According to Seven Marine’s promotional literature, a pair of the 557 hp outboards can cruise at speeds where triples are running wide open, yielding better fuel economy, as well as the potential for even greater speeds.

With this in mind, I was surprised that Seven Marine brought a single-engine boat for driving impressions. We ran the boat with 200 gallons of gas and five people aboard, including Sandy Ballou, vice president for Seven Marine, who asked that I not record full test numbers during this particular sea trial. I did, however, gather some top line performance data.


Propped with a Hering 26” pitch forged stainless six-blade wheel, the 557-powered Sea Hunter achieved a top speed of 52 mph at 5200 rpm while running in light chop with an air temperature of about 80 degrees F. Ballou claims that the 557 burns approximately 55 gallons per hour at wide-open throttle.

Our boat had a tendency to heel over to port due to prop torque, particularly during hard acceleration. This is not unusual for a deep-V hull with a single outboard, so no marks against the 557 for this. My only thought is that the Sea Hunter 29 is made for twins, as the opposing prop rotation will help level out the ride.

The 557 was quiet at idle. I recorded 68 decibels (DBa) at idle in gear. However, as engine speed increased to 1,200 rpm, an annoying whine became audible. By the time we reached top speed, the high-pitched sound was quite loud. I recorded 94 DBa at 5,200 rpm.


Ballou explained that the whine was due to straight-cut gears in the lower unit of the pre-production model, and that production outboards will have helical gears that eliminate this noise.

We are anticipating a full test on Seven Marine’s 557 production outboards sometime this spring.

Photo Gallery: Seven Marine 557 Unveiling at the 2011 Miami International Boat Show


Video: Seven Marine 557 at the Annapolis Boat Show


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