Inboard vs outboard — what’s best?
So, what's the difference between an inboard and an outboard, and which is better?
By their very nature, boats need power for motivation. Ancient mariners drew on the wind and muscles, but by the late 1700s century, an inboard steam engine-powered paddle boat hit the water in the US, and 60 years later, the first screw propeller-driven steamship launched. We no longer had to rely on the weather to go to sea.
Most historians credit the first modern-style powerboat to Germans Gottlieb Daimler and Friedrich Lürssen in 1886, who set their timber launch, Rems
The roll call of familiar names continues with Ole Evinrude, who unveiled the first successful outboard engine in Milwaukee, US, around 1907. Evinrude made outboards until the business ceased production in 2020 during the pandemic as the last of the significant two-stroke engine suppliers.
The ins and outs of engines
So, what's the difference between an inboard and an outboard, and which is better? The answer is three-pronged because inboards separate into the pure inboard and a sterndrive, a mix of in and outboard. The inboard is usually an automotive engine sitting low in the boat and driving through a gearbox to a shaft that passes through the hull to a propeller. A sterndrive has the same style engine, which connects to a drive unit that extends through the transom and houses a lifting leg and propeller. Outboards bolt to the transom and combine engine, gearcase and propeller housing.
Inboards
Once established, boating technology grew quickly, and inboard power was common across recreational and commercial activities. Because of their relatively large engine size, most ships benefit from a shaft drive design where the weight of the inboard motors is low in the hull. The weight aids stability, and the shaft drive is simple and efficient.
Up until the 1960s, the majority of powerboats used inboard engines. These days, most recreational boats with an inboard engine are specialist craft like high-speed ski and wake boats where the extra torque of a big V8 pulls skiers out of the water effortlessly and the low position of the prop gives a clean wake. A drawback of the shaft driven inboard is that it needs a rudder to steer the hull of the boat, so reversing and close movement around the dock can be tricky.
These days, it’s mainly recreational boats longer than 40 feet that retain the inboard concept. But as we shall see, that's changing as more powerful outboards are released.
Talking sternly
Volvo Penta gave us the sterndrive in 1957, and that’s a story in itself because Mercury was offered the concept and ignored it. But the adaptation in the ‘60s of the sterndrive in the US revolutionised boating. By combining the external mechanics of an outboard leg with the reliability and power of a big engine, boats were easier to drive, faster and more fun. Outboards of that era lacked power and dependability, so sterndrive brands from the US like Sea Ray, Chris-Craft and Bayliner thrived and were household names in Australia.
The advantages of the inboard/outboard setup of the sterndrive include the open space at the transom with the addition of full-width platforms for swimming or preparing for water sports. And with no engine blocking the view rearward, it made it safer for observers to watch skiers out the back. The trimmable leg also gave better drive and economy than a pure/true inboard, making the boat easier to beach — a significant benefit for family days on the water.'
The aesthetics of sterndrives play a big part in their popularity. The seamless integration of the engine and drive creates pleasing lines and simplicity of use. The layout is more like a car, with the engine hidden under a sun pad and stylish seating wrapping around the cockpit. Classic Mediterranean cruisers like the Riva reek of a laidback, sophisticated lifestyle with no tacky engine to spoil the effect. The boat is so sleek it looks like it could glide across the water of its own accord.
Outside influence
As much as anything, rules around emissions contributed to the advance of outboards. Twenty years ago, most brands ran two-stroke engines, and power above 250hp was uncommon. The United States Environmental Protection Agency clamped down on two-stroke emissions, and in 2003, Suzuki hit the market with their clean-burning DF250 direct injection four-stroke, and the days of two-strokes were doomed. Since then, outboard manufacturers have put all their eggs into four-stroke development to the detriment of the automotive style inboard engine. Outboard power has increased exponentially with higher output engines and multiple power plants bolted to ever larger craft.
As well as advances in power, outboard benefits include giving vast amounts of storage where the inboard engine would sit. But they lose by taking up transom real estate where a platform might reside.
Times they are a-changin’
Sydney boat dealer Mark Chapman is a stalwart of the local scene, and when we spoke to him recently, he was putting the finishing touches to the latest Beneteau GT36 with twin V10, 350hp Mercurys on the back. Only a few years ago, this size and larger boats were the sole domain of inboard power. Chapman has seen the marine industry undergo massive change in the last decade. Ten years ago, almost every family cruiser was a sterndrive, but these days only 30 per cent of buyers opt for that option and for most of them, it's about the style and the quieter running of the inboard engine.
But he sees outboard boats winning customers as times change.
"Buyers who used to insist on an inboard now say they prefer the big Mercury outboards we offer. They used to worry about the lack of a swim platform, but now they just bring a lily pad and enjoy the benefits and simplicity of ownership."
He added that you can’t leave an inboard on a mooring in Sydney Harbour without the leg being covered in coral within a year. The outboard comes right out of the water, he explained. “Add in higher maintenance costs on the sterndrive and better six-year warranty as opposed to two years in saltwater conditions for a Mercruiser sterndrive, and the costs start to add up," he confessed.
Ski Legend
Rod Bickerton crafts class-leading social and race ski boats at his Force factory on the banks of the Hawkesbury in western Sydney. If anyone knows how to make a boat go fast, it’s him. Rod advised that a sterndrive still has a place in performance boating. “Our top end race boats like the Superman can achieve 120mph with a 2000hp V8 engine carrying a full tank of fuel and towing two skiers over courses like the Sydney Bride to Bridge. You just can’t locate large size outboards on a ski boat to get similar performance; they are just too heavy. The V8 engines sit low in the hull for fantastic weight distribution so they are easier to drive and a lot safer at speed.”
He told us the only 15 per cent of buyers opting for an inboard social ski boat these days were those who liked the classic sound of the inboard V8 that you just can’t get in an outboard.
Not quite a game changer
Even game boat owners are moving to outboard-powered craft, and Chapman cites the example of a Bertram 63 owner with twin diesel inboards who is opting for a 50' Scout with triple 600s. It will get him to the shelf quicker, with less cost, and save 75 per cent on the maintenance bill.
Chapman pointed to European brands like De Antonio with designs that cover the outboard engines with decks for all the benefits of a sterndrive’s swim platform. With advances like this, you wonder if the days of the inboard in recreational boating are nearly gone.
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