No other marine engine manufacturer offers a broader selection of propulsion options than Mercury Marine®. Those options fit into three main categories – outboard, sterndrive and inboard. So what’s the difference, and why so many options? Let’s take a look at the advantages, and most popular applications, for each propulsion system.
Inboard power is the classic, original marine propulsion system. A gasoline or diesel engine is located within the boat, and power is transferred to the propeller by a shaft that passes through the bottom of the boat hull. A separate rudder steers the boat.
At one time, almost any pleasure boat bigger than a skiff had inboard power. If there are classic wood runabouts on your lake, they are almost certainly inboard-powered. In the early years of pleasure boating, only converted automobile or aircraft engines offered enough horsepower to move even midsize runabouts. That began to change in the mid-1950s as outboard motors became more powerful.
Today, inboard power remains most popular for specialized tow sports boats, which may be powered by a Mercury® MerCruiser® Tow Sport V8 inboard engine. Inboard power offers a number of advantages for tow sports. The engine makes a lot of torque, and the prop is always in undisturbed water under the boat, both of which help pull water-skiers and boarders quickly up on plane, and hold well against the strain of the tow line. An inboard can also provide power without creating excessive turbulence behind the boat, which allows builders of specialized wake sports boats to shape the hull to create the most desired wake for skiing, boarding or surfing.
Today’s technology from Mercury also helps to overcome some inherent challenges with inboard boats. For instance, a classic, single-prop inboard can be tricky to handle around the dock unless it’s equipped with Mercury Joystick Piloting for Inboards (also available for dual-inboard boats). The Joystick Piloting technology allows the engine to work with bow and stern thrusters to provide ultimate vessel control and a superior driving experience for the boater.
The sterndrive engine (sometimes called an inboard/outboard, or I/O) was devised in the early 1960s as a power system that combines the torque of an inboard engine with a steerable and trimmable drive unit mounted on the transom. This allows for easy, confident maneuvering at low speed. The trimmable drive improves performance and economy, and because the drive can be trimmed out, or raised, it allows the boat to be beached. Today, Mercury MerCruiser gasoline sterndrive engines range from 200hp to 430hp. Mercury Diesel engines for sterndrives are offered from 115hp to 550hp.
Mercury offers a number of MerCruiser drives designed for specific applications, from family runabouts to performance boats to heavy cruisers and house boats. The newest MerCruiser drive, the Bravo Four S®, features dual forward-facing propellers. It's an ideal choice for wakesurfing and other tow sports that also lets you enjoy a sterndrive boat’s deeper hull and steerable, trimmable drive.
Because the drive unit is mounted low on the transom, most sterndrive boats have a full-width swim platform, which can often be expanded with an optional extension to create even more space for lounging, swimming or preparing gear for tow sports.
“Most people don’t spend all of their time moving on the boat,” said Gary Nichols, CEO of the six Nichols Marine locations in Oklahoma and Texas, each a Mercury Authorized Dealer. “They are rafting up with friends or hanging out at the beach or sandbar. When there’s an option, these owners choose a runabout or deck boat with MerCruiser sterndrive power to get the unobstructed swim platform and sun lounge over the engine. They also really like the clean lines of the boat. You can’t see the engine at all.”
Sterndrives once had a reputation for being prone to corrosion-related issues in saltwater, but Mercury has significantly improved corrosion resistance on its latest engines and outdrives. The Mercury Precision MerCathode® system, an industry-first that comes standard on MerCruiser Bravo® drives and is available for MerCruiser Alpha® drives, provides automatic protection against galvanic corrosion. The SeaCore® system, the industry’s premier saltwater corrosion protection system, is designed to ensure a MerCruiser engine stands up to the rigors of the saltwater environment over the long haul. All MerCruiser sterndrives come backed by an industry-leading three-year corrosion warranty.
An outboard is a dedicated marine engine that is attached directly to the stern of a boat, and today many family boat models are offered with a choice of outboard or sterndrive power. Mercury Marine has its roots in outboard power. The company was founded as Kiekhaefer Marine to manufacture Mercury outboard motors – two 3hp singles and a 6hp twin were introduced in 1940.
Originally intended only to power small fishing boats and runabouts, as outboard motors have become more powerful they have often replaced inboard and sterndrive engines on larger cabin cruisers, day boats and high-performance boats. Today, the Mercury outboard lineup is the broadest in the industry, from the portable 2.5hp FourStroke outboard to the mighty V12 600hp Verado® outboard, and Mercury Marine has been a leader in the development of modern, lower-emissions four-stroke outboards.
“Modern four-stroke outboards are such an improvement over the two-stroke motors of a generation ago,” said Nichols. “They are clean, quiet and fuel efficient, and offer more power than ever. Customers who appreciate the technology of new Mercury motors tend to prefer outboard power when it’s an option.”
Many new boats may be rigged with three or more outboards that, when combined, make more power than the biggest pair of sterndrive engines available, resulting in performance that was once unimaginable. A new Mercury outboard is more efficient and more powerful and feature-laden than the motors offered just a few years ago, all reasons outboards have become more popular on more types of boat.
Because the entire outboard engine is located outside the boat, more of the cockpit can be devoted to seating or gear storage, livewells and other features in the space a sterndrive or inboard engine would occupy – one reason outboard power has always been a popular choice for fishing boats. The key trade-off for outboard power on family boats is that the motor intrudes on the swim platform. With sterndrive or inboard power, the boat can be designed with a flat, full-width platform that many boaters prefer for swimming and lounging.
An outboard is also self-draining, which makes it easy to prepare for winter storage.
“In our region, where winter is not severe, one reason outboards are popular is because they don’t require the more-extensive winterization needed for a sterndrive engine,” said Nichols. “Our customers can easily get an outboard-powered boat out for a Christmas boat parade, or a really nice winter weekend.”
There’s No Wrong Choice with Mercury Power
Inboard, sterndrive or outboard, all Mercury Marine propulsion systems incorporate design and technology features to make boating easier and more enjoyable. Select Mercury and MerCruiser engines also offer access to a wide range of SmartCraft® digital technologies, which provide boaters with incredible control over their on-water adventures.
Mercury has long been a leader at building reliable, easy-to-maintain marine engines. Whether you do your own maintenance or take it to a service pro, it's simple to keep a Mercury outboard or MerCruiser engine running at its peak. When you lift off the cowl or open the hatch, you’ll find service points are color-coded so they are easy to find. To make maintenance even easier, there’s a scannable QR code on the engine for links to DIY service videos you can watch on a mobile device.
Ultimately the type of boating activity that fuels your passion to be on the water – fishing , skiing, tubing, cruising or high performance – will determine the ideal choice in Mercury Marine power for your boat and boating lifestyle. For more information on the marine power options, visit your local Mercury Authorized Dealer