STERNDRIVE VS. INBOARD VS. JET VS. OUTBOARD

The debate between sterndrive and inboard propulsion has raged on for decades. When I was growing up in my father’s boat dealership we did not like sterndrives. I grew up in an age where the inboard propulsion system was king but later the sterndrive became the propulsion of choice in general purpose pleasure craft up to roughly a 37’ Length Overall. This position paper outlines a discussion I’ve had with others in my profession and is not the final word but rather a carefully thought out attempt to inform the consumer.

What is an inboard?
With inboard propulsion an automotive engine is inside the boat connected to a transmission. A  propulsion shaft goes from the transmission to a propeller outside the boat. The boat turns using a rudder. The steering wheel is turned by the captain who turns the rudder. The propeller pushes water past the turned rudder and that’s what turns the boat.

What is a sterndrive?
With a sterndrive propulsion system an automotive engine is also inside the boat but it’s attached to a sterndrive (also called outdrive). The drive unit is the transmission AND the propulsion. When the captain turns the steering wheel the entire drive turns.

Some of the arguments for and against each

Back in the day when we sold inboard boats exclusively, inboards were much more dependable than sterndrives. The sterndrives have much more machinery outside the boat than inboards do and that used to make them very troublesome—on the other hand they were a lot more fuel efficient  and had a much tighter turning radius.

Fast forward to now
The company I sell boats for is really trying to sell more boats that work for wakeboarding and surfing. Surfing is replacing wakeboarding and waterskiing as the primary type of water boarding activity because of its simplicity and safety. Every boat builder is attempting to capture this way to have fun on the water. As a result I was looking at a Mastercraft boat brochure—Mastercraft is a premium inboard tow boat builder and if you're in the market for an inboard tow boat they definitely merit a look. Inboard boats dominated the waterskiing boat market because they dominated the tournaments. They make some compelling arguments for inboard tow boats, some of which are special to the Mastercraft brand:

1. The inboard boats draw less (they need less water to float) than a sterndrive if the sterndrive is all the way down.
2. Mastercraft’s inboard system turns more tightly than a lot of sterndrive boats.
3. The inboard tow boats put out a flatter wake for waterskiing.
4. The system is simpler if you strike a  submerged object so it’s cheaper to fix than a sterndrive unless the  drive manufacturer uses a drive saver coupler. For example, Volvo Penta uses one in their SX, DP-s and OSi drives.
5. Because of several factors, an inboard boat will hold a speed more easily than a sterndrive. This is mitigated by the use of a cruise control unit called Perfect Pass for more experienced wakeboarders and surfers.
6. Because of the way tow boats are built they can create some monster surfing waves!
7. Tow Boats tend to have really flashy exteriors and interiors.

Compelling arguments for the sterndrive boat:

1. The sterndrive boat will go faster than the inboard with the same horsepower.
2. The sterndrive boat will also go faster at any given RPM than the inboard tow boat. This means the sterndrive uses less fuel. In some cases it uses a lot less fuel. On some boats we sell the difference is 20%-25%!
3. Parts are more readily available for sterndrives—whether the Volvo or Mercruiser brand—and that means less down time.
4. Sterndrive boats have more versatile seating arrangements.
5. Better sterndrive boats turn almost as tightly as the best inboard tow boats.
6. Sterndrive boats tend to run better in rough water due to their sharper deep vee hulls. This is meaningless on a small lake perhaps but on a larger lake or tidal water it’s important.
7. An inboard boat goes in reverse to one direction no matter the position of the wheel. This is harder than with a sterndrive, where reverse thrust is directional.

In both cases the perception of safety is the same. The propeller on and inboard boat is up under the boat and the propellers on a sterndrive surf drive face forward away from the rider.

What about regular sterndrives?

Regular sterndrive boats are famous for their “back porch” As we move forward more and more attention is paid to making three entertainment zones: one in the bow, one aft of the windshield, and one from the engine hatch to the water. Steps are becoming more predominant as a way to access the water as opposed to ladders, and that takes a lot of the perceived danger away about the props. Of course, I take a practical approach to props: if someone is in the water the engine is off no matter what I’m driving! Because the boats with the forward-facing sterndrives draw more water and have more surf-related accessories, a regular single or duoprop sterndrive might be the better and lower cost alternative.

What about Jet Boats?

Jet boats have unique cockpit layouts and of course no propeller. They turn on a dime. Some versions such as the ROTAX motor in the Vortex and Scarab brands have a true neutral, while some others do not. This to me is an interesting safety feature. Jet boats are less fuel efficient than sterndrives and can be louder and there is of course no way to change the attitude of the bow by raising and lowering the drive so the boats can be wet depending on the wave action.

Some jet boats can be equipped to surf behind. For example, Vortex has what’s called an Aerial Surf Platform, which produces a sweet surf wave with the utmost of simplicity.

What about Outboard Runabouts?

Outboard runabouts have gained in popularity as the price between them and sterndrives becomes roughly equivalent. People who prefer outboards like that the generally have less draft, and can be tilted all the way out of the water so they don’t get dirty. In addition, it is simple to freeze protect an outboard. Interior layouts vary: some runabouts are designed from the keel up so the interior space is increased. Others are based on a sterndrive boat that was developed first. That opens up what used to be the engine room for copious amounts of storage.

Any boat that does what it’s designed to do is a successful design. I sincerely hope you found this article informative.

Best,

Joe