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The Evolution Of Outboard Engines: A Look At Past, Present, And Future Developments

Nearly 20 years ago, stricter emission limits sparked a 4-stroke technology revolution that changed outboards forever. The propulsion evolution has only accelerated since then. Let's get you up to speed.

Illustraion on the left: a 2004 60-hp Mercury outboard with interior cutaway, on the right, 400 hp Mercury V6 outboard with interior cutaway shown

My, how you've-grown! On the left is a 60-hp Mercury outboard from 2004; on the right, 400 hp is packed under the cowling of a Mercury V6 outboard. (Illustrations: Mercury Marine)

Technological evolution in our recreational boating world has been punctuated by seismic events such as motorboats taking off in the 1930s, or the fiberglass hull revolution in the '50s. But few segments of the marine industry have seen more dramatic changes over the past 30 years than outboard engines.

To get a sense of how we've come so far, so fast, we spoke with two industry insiders who've surfed the curl of each new tech wave for decades. Tim Reid is vice president of product development and engineering for Mercury Marine. David Meeler is the new product introduction manager of the Yamaha Marine Engine Systems. Few people have as much insight into the past, present, and future of outboard engines.

BoatUS: How do four-stroke outboards from 20 years ago compare to 2023 models?

Tim Reid: The major differences between early four-stroke outboards is the refinement in design to maximize power and minimize weight. Twenty years ago, a 200-hp outboard would've been much larger and likely 100 pounds heavier. Computer-aided engineering capabilities were used then, but the level of detail and time needed to calculate stresses was relatively simple. Today's calculation speed and fidelity allow engineers to run through many optimization simulations to extract every ounce of excess material (aluminum and steel) to lighten the engines, yet meet all durability requirements. Typically, a new engine block undergoes more than 40 iterations to optimize its structure to exceed endurance targets including all thermal, cylinder pressure, piston skirt, and shaking stresses.

David Meeler: Previously, outboards were built off a two-stroke structure. As EFI [electronic fuel injection] and then DFI [direct fuel injection] were added to these designs, the primary concern was getting fuel into the engine. Today, in order to maximize the power and efficiency of the four-stroke outboard, engineers must consider all four phases of combustion — intake, compression, power, exhaust — as well as minimizing drag, strength vs. weight, and emissions. It's no longer just about the outboard itself. Engineering processes have expanded to more of a "power system" mentality within the industry, led by customer demand. With technology being added into controls such as autopilots and full maneuverability joysticks, so much more holistic thought must go into the design and engineering of outboards with each passing decade.

Three of Yamaha's 450-hp V8 XTO Offshore outboards running on the stern of a powerboat with blue water churning in the background

Yamaha's new 450-hp V8 XTO Offshore outboards feature a three-phase charging system that delivers enough output to replace an on-board generator.

How much horsepower can marine engineers pack into an outboard? The 300-hp threshold was mind-blowing, then came 500, then 600 horses. Is there a limit?

D.M.: Two key factors play in here — size and weight. Over the years, outboards got more powerful, so boats got bigger. Consumers liked the bigger boats, so the outboards got even more powerful. At some point, the balance between size of the boat and size of the outboard, relative to the amount of power needed, reaches a practical limit before it reaches a design limit. Engineers never stop working on the next thing. Lighter materials, better engineering, and advanced technologies will all play a role in "how big will outboards get?" in terms of power.

T.R.: Like in all consumer goods, if there's market demand, it will be filled. In the past, there have been perceived limits on outboard power. It would be naive to believe that higher power products are not possible. For a long time, the industry thought 250-hp outboards was plenty.

What about electric propulsion? Is it destined for mainstream acceptance, or will it remain a niche market?

T.R.: Ultimately, yes, it will become mainstream. But we need to see a step change in batteries — that's key. Mercury is working on it now in lower horsepower niches, having just launched our small electric outboard, Avator. But I can't say how many years it will take or when it might happen. As the battery storage density advances, we'll see broader acceptance of electric propulsion. Like all mobility sectors, recreational boating will diversify into electric propulsion.

Product photo: Avator, Mercury Marine's 7.5e (3.5-hp equivalent) electric outboard

Avator, Mercury Marine's new 7.5e (3.5-hp equivalent) electric outboard, is just the start of bigger electric motors from Mercury.

D.M.: As technology and customer demand advances, more applications for electric propulsion are discovered. The energy density of current battery technology is the limiting factor at this time, particularly because of the high drag environment of operation. When technological capability catches up to expectations and demand in this area, it will most certainly lead to proliferation in the market.

What about a hybrid outboard? Hybrid vehicles work well on roads, but is it a workable solution in recreational boats?

T.R.: In a hybrid car, the engine displacement is intentionally minimized to more closely match the required power under highway conditions. This small-displacement engine provides improved fuel economy but is challenged to provide acceptable acceleration. Coupling an electric motor to augment the small internal combustion engine's torque provides acceptable acceleration. Around town, the electric motor can provide much of the propulsion until the battery gets low and then the car can recharge the battery with the internal combustion engine and with regenerative braking.

Hybrid marine-drive systems can be very challenging because you have two systems and twice the complexity in the corrosive marine environment. In 2010, Mercury produced a one-off hybrid boat demonstrator and displayed it at boat shows. But we found you need all the available power when cruising, and customers were reluctant to give up top speed — the physics is just very different from rolling down a road — and what takes 30-hp on land requires almost 200-hp on the water. So again, batteries are a limiting factor.

However, when the power isn't going to the propellers, hybrid systems work very well for electrical demands, which is what our Fathom energy management system containing lithium-ion batteries, sensors, switches, and controllers is all about. The new Verado V10 outboard, paired with Fathom allows the removal of the generator. The V10 Fathom system doesn't use the stored energy to move the boat, but it does allow for both shore power and electricity from the outboard alternator to power all the electrical systems on the boat within the capacity limitations of a large li-ion battery bank.  Once the battery gets low, the captain is alerted that the engine should be started to recharge if the engine is off, otherwise the system switches to charge mode automatically. This automated system provides silent and vibration-free house power. We do see hybrid as the future of fulfilling electrical demands on boats.

D.M.: Nothing is off the table as far as electrification as it moves further into marine power. Engineering currently has design limits, such as drag and current battery power density levels. But design limits are what spur engineers to change the status quo.

In your opinion, what recent technological development has most benefited outboard boaters?

T.R.: Joystick control has been a game-changer that enables more precise control of recreational boats. The joystick enabled intuitive control of multi-engine boats and gave skippers the confidence to maneuver their vessels in tight quarters. They've also enabled people to drive bigger and bigger boats, which is partly why we see these huge 50-foot and larger outboard boats today. The boats have gotten bigger and bigger, and we've chased them with more and more horsepower, but it's joystick controls that make it possible for typical boaters to be comfortable operating large boats.

D.M.: System integration with products such as Yamaha's Helm Master EX system and advances including integrated digital electric steering in place of less smooth cable hydraulic steering. They're both aimed at helping boaters master the art of controlling a boat by providing a fully integrated control system with the outboards, advanced maneuvers for docking and fishing, helping boaters realize greater use and less stress while boating.

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Rich Armstrong

Senior Editor, BoatUS Magazine

A journalist by training, BoatUS Magazine Senior Editor Rich Armstrong has worked in TV news, and at several newspapers, then spent 18 years as a top editor at other boating publications. He’s built a stellar reputation in the marine industry as one of the most thorough reporters in our business. At BoatUS Magazine, Rich handles everything from boat and product innovation and late-breaking news, to compelling feature stories, boat reviews, and features on people and places. The New Jersey shore and lakes of lower New York defined Rich's childhood. But when he bought a 21-foot Four Winns deck boat and introduced his young family to the Connecticut River, his love for the world of boats flourished from there.