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Power update: outboards, sterndrives

There’s a lot going on in these engine categories, from the world’s biggest 4-stroke to a compact I/O

Power update: outboards, sterndrives

There’s a lot going on in these engine categories, from the world’s biggest 4-stroke to a compact I/O

Last month we examined two pod propulsion systems — Volvo Penta’s IPS and Cummins MerCruiser Diesel’s Zeus — and looked at how they are radically changing the landscape for boats between 35 and 90-plus feet. There’s also been a lot going on in the outboard and sterndrive markets. Let’s consider a few of these new engines and how they can make a difference in your life on the water.

I’ll say one thing upfront: Whichever engine brand or technology you choose, it seldom makes sense to get the smallest engine offered by the manufacturer. People often test-ride a new boat (if they do at all) when it’s got 10 gallons of gas in the tank and two people on board. While the boat might get up and go when so lightly loaded, you can rest assured the 135-hp 4-cylinder sterndrive in your 18-foot bowrider is going to struggle just to get up on plane with a full load of fuel, passengers and gear, and forget about pulling a skier or wakeboarder out of the water.

The upgrade to the 190- to 220-hp V-6 is definitely a good idea. While the temptation to save the $3,000 to $6,000 it would take to get the carbureted or EFI V-6 upgrade can be strong, underpowering a boat is a sure way to end up regretting buying it in the first place.


Outboards are lightweight, easy to change out and fast for their horsepower. Their lower units, like a sterndrive’s, produce very little drag and are trimable, so they perform very well. They’re also expensive for their horsepower and project 4 to 6 feet abaft the transom, which can make it hard to work a fish off the stern. But their reliability, ease of access and maintenance, and light weight make them very popular for boats ranging from 6-foot tenders to 40-plus-foot offshore sportfishing machines.

Just a few years ago, most outboards sold in the United States were carbureted 2-strokes. These are the smelly, smoky, hard-to-start beasts that many of us grew up with. Actually, I never especially thought of them as belch- and stall-prone engines, but that’s what they were (and are). For all their faults, though, they were inexpensive to buy and, with reasonable care, would last for decades — at least in fresh water.

The big change we’ve seen in the last four years is that two kinds of outboards have come to dominate the marine market: direct injection (DI or DFI) 2-strokes and electronic fuel injection (EFI) 4-strokes. Both of these engine classes start virtually instantaneously, produce minimal fumes, are much quieter and run much cleaner, with hardly any smoke and no more oil slick trailing behind the boat. By all accounts, they’re also more reliable.

We have two things to thank for these improvements in our lives on the water: the federal government, which has mandated lower engine emissions; and consumers, who evidently have mandated the same thing, along with improved reliability and efficiency. Whether you opt for a DI 2-stroke or EFI 4-stroke, these engines are light-years ahead of the old carbureted and EFI 2-strokes that constituted most of the market just a few years ago. With their sophisticated fuel delivery systems, more of the fuel gets turned into forward thrust, rather than smoke and an oily wake.

Evinrude has put all its eggs in one basket, manufacturing 2-stroke outboards exclusively. These high-tech direct-injected engines require very little maintenance and, like other DI 2-strokes, produce very low emissions, deliver good economy, run quietly and generate the whiplash acceleration that 2-strokes have always been known for. The outboards have proven very popular among pontoon and bass boat owners, as well as offshore saltwater sport anglers.

Whichever brand you might be considering, all of the DI 2-strokes and EFI 4-strokes from Evinrude, Mercury, Honda, Yamaha and Suzuki typically deliver very good service. To get the best possible performance, I recommend avoiding carbureted 4-strokes and EFI and carbureted 2-strokes.

While Evinrude has carved its own niche quite effectively, the fact that most of the news in the outboard world has focused on 4-strokes is because that’s where most of the demand is. Accordingly, that’s where the majority of outboard manufacturers are concentrating their efforts. The 4-strokes are also getting more powerful; Suzuki’s 300-hp, Mercury’s 300-hp Verado and Yamaha’s F350 allow boatbuilders to build bigger and faster boats.

So it’s no surprise that the biggest news in this market is also the biggest engine — Yamaha’s V-8, 350-hp behemoth, currently the most powerful outboard in the world. A pair of F350s will take the place of triple 250s in a 34- to 40-footer, and a single will stand in for twin 150s or 200s in a 26- to 28-footer. Designed from the prop up as a marine outboard, the F350 has a whopping 5.3-liter displacement (read: long engine life) and weighs an equally whopping 804 pounds. But keep the weight in perspective; the F350’s power-to-weight ratio (2.297 pounds/horsepower) is actually slightly better than the 592-pound Yamaha F250 4-stroke (2.368 pounds/horsepower). The F350 will let outboard fishing-boat builders like Grady-White and Pursuit build bigger, heavier boats, which is a good thing, since these bigger, more capable boats are in strong demand in what is otherwise a downturn in the industry.

Also on the 4-stroke front, Mercury has increased the rating of its flagship Verado to 300 hp, matching Suzuki’s 2-year-old offering, and has recently announced that its engineers have improved the turbocharged Verado’s fuel economy, which wasn’t stellar at high cruise speeds when the engine was introduced. One thing to love about the Verado is the SmartCraft DTS (digital throttle and steering) controls. These are the smoothest-shifting outboard engine controls I’ve yet come across, with none of the shifting resistance and clunking experienced with cable shifts. You can steer a trio of 275-hp Verados (as I have on a 351 Triton) with your fingertips.


There are two major players in the sterndrive market: Volvo Penta and MerCruiser. Both produce a wide range of gasoline and diesel sterndrives, and both have been busy introducing new power. Both MerCruiser and Volvo use GM blocks for their gas engines. On the diesel side, MerCruiser uses engines built by other manufacturers, like Yanmar and Cummins, while Volvo makes its own engines. Both companies manufacture their own drives, or lower units.

Sterndrives are popular because, like the outboard, their lower units produce very little drag, so they’re more efficient at higher cruising speeds. They also are trimable, which means the lower units can be trimmed out or in to raise or lower the bow, adding a lot of flexibility for the operator in different sea states and conditions of loading. Compared to an outboard, the sterndrive is heavier and not as fast for a given horsepower, but the boat’s center of gravity is lower and the transom is not as obstructed. In fact, with a jackshaft — allowing the engine to be mounted farther forward in the boat — the transom can be kept relatively clear.

While Volvo Penta and MerCruiser make single-prop units for various applications — including smaller, less-expensive boats and heavier, slower cruisers — both offer counter-rotating propeller drives, called Bravo III by MerCruiser and DuoProp by Volvo. For most sterndrive boats capable of up to 65 mph or so, these counter-rotating drives are the way to go. They accelerate strongly (blade loading is spread out between the two props, which also minimizes cavitation), and the props cancel out side force, so there’s no torque to make a light, single-engine boat heel at high speed. And, just as importantly, they handle superbly at slow speed, backing equally well in either direction and tracking better with the extended underwater surface area of the drive.

Mercury recently introduced its low-profile Vazer single-prop sterndrive, designed for smaller boats traditionally powered by outboards. It has a 4-cylinder, 100-hp GM Vortec gas engine with closed-loop cooling for its engine block, cylinder head and aluminum exhaust manifold, which makes it well-suited to both salt- and freshwater applications, and it has an all-new lower unit. The engine is tilted 50 degrees to create its low profile, and it has a composite (corrosion-proof) inlet manifold.

Mercury hopes builders will design boats around the engine — for example, fitting it under aft seats and flush decks. Assuming a high degree of durability, the Vazer is a good choice for small runabouts that benefit from a low stern profile, which in opening the cockpit to the swim platform (like the Yamaha 210 and 230 SX waterjet runabouts) adds a competitive advantage for towing tubers and other low-power-demand, stern-oriented activities. The Vazer is small at just 100 hp, but it will be well-suited to pontoon boats and perhaps in twin installations in runabouts.

If it’s a 90-plus-mph high-performance boat you want, then you’ll also be looking for a MerCruiser. Since the 1960s Mercury has made its name on the racing circuit, both with outboards and sterndrives. Even today it gets a lot of marketing sizzle by associating itself with racing brands like Fountain and Baja. MerCruiser’s racing division produces beefed-up and streamlined racing engines of more than 1,000 hp and drives capable of speeds in the 140-plus-mph range.

The biggest news in the diesel sterndrive world is from Volvo, with its new 300-hp D4 and 370-hp D6 engines coupled to its DuoProp DPH sterndrives. (A DPR version is available for speeds of more than 57 mph.) The 4-cylinder D4, about the size and weight of a big-block gas engine, has a number of upgrades from the previous D4, all geared to increasing durability and reliability. These upgrades, including remarkably effective new engine mounts (I ran a D4-equipped boat a few weeks ago), produce the smooth running of a 6-cylinder engine. These 300-hp diesels will deliver the steady-state cruising speed of a pair of 400-hp gas engines and burn substantially less fuel in the process. Their 4-cylinder design also allows them to be installed in a shorter engine room, leaving more room for accommodations.

Just as remarkable is the Volvo D6 sterndrive package, which at 370 hp is the most powerful diesel sterndrive available. The D6 DuoProp package weighs just 1,698 pounds and is rated for applications to 69-plus mph. Packing so much diesel horsepower into a sterndrive package is a real accomplishment, in part because of the tremendous torque (651 foot pounds for the D6) the lower unit has to be able to absorb for thousands of hours. The drives have been strengthened to handle the extra power.

The D6 and D4 have common rail fuel delivery for a smoother, quieter and cleaner-running engine. Mercury offers its Bravo III sterndrive that can handle up to 320 hp when coupled to a Cummins QSD4.2 (4.2 liter, 3,800 rpm) common rail diesel or similar Yanmar offering.

One great thing about having up to 370 diesel sterndrive horses available is that a single sterndrive can easily drive a 30-plus-foot boat to 34-plus-mph speeds while burning relatively little fuel in the process. While it used to be that 28 feet was the biggest express cruiser that a single sterndrive could handle, this figure now is more like 30 to 35 feet, depending on the boat’s displacement and target cruising speed. If you want either exceptional range or economy in a bigger cruiser, the 370-hp Volvo DPR can’t be beat.

Whichever power you’re looking for, there are a lot of good packages available that promise many years of clean, quiet and reliable service.

Eric Sorensen was the founding director of the J.D. Power and Associates marine practice and is the author of “Sorensen’s Guide to Powerboats: How to Evaluate Design, Construction and Performance.” A longtime licensed captain, he can be reached, and his book purchased, at