Inboard vs. Sterndrive: Pros & Cons of Each Propulsion System
Boat propulsion systems can include inboard engines, outboard motors, outdrives also called sterndrives, jet drives and electric pod drives. Here, we’ll look at the pros and cons of inboard engines and sterndrives engines and how each is best used.
Post summary:
- Definition of inboard engine & sterndrive engine
- Pros & cons of sterndrives
- Pros & cons of inboards
- How to choose between inboards and sterndrives
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Definition of inboard engine & sterndrive engine
Inboard engines are placed low in the hull and more toward the middle of the boat. The engine (usually a diesel but could be a gas motor) is connected to the propeller via a shaft or in some cases a Saildrive pod/transmission. The propeller washes water over a rudder which in turn steers the boat. The propeller is fixed at a certain depth below the hull.
Sterndrive engines extend out behind the boat in a transmission and propeller combination. The unit creates directional thrust which means the whole thing turns so there’s no need for a rudder. Sterndrives can trim (lift) the propeller to various angles and depths at the transom.
Pros of sterndrives
- The placement of the engine farther aft in the hull creates more room inside the boat and that increases the variety of seating options and better use of space.
- Trimming the drive up means the boat can venture into shallower waters and is easier to load onto a trailer.
- Sterndrives may use less fuel to generate the same horsepower and may be faster than inboards of the same size.
Cons of sterndrives
- The most significant argument against sterndrives is that the lower unit is almost always exposed to water, thus requiring more maintenance over time.
- For tow or water sports boats, the propeller is closer to the rider behind the boat which could pose a hazard.
Watch this video on sterndrive engines
READ MORE: How to Rent Out Your Boat? (How Much Can You Actually Make?)
Pros of inboards
- Inboard boats carry the weight of the engine inside the hull which lowers the center of gravity and provides greater stability for the boat both at rest and in motion.
- Inboards tend to be more precise at holding a given speed which becomes key during certain uses like running a slalom ski course during a competition.
- Inboards create lower and flatter wakes which is good for water skiers, although not as exciting for wakeboarders.
- Inboards may be quieter since the engine is low below the waterline and away from the driver and guests.
Cons of inboards
- Without directional thrust, inboards suffer from prop walk in when in reverse which means they pull in one direction rather than backing straight.
- Inboards can’t turn as tightly as sterndrives where the thrust comes from the back rather than the middle of the boat.
- Inboards tend to draw more because the propeller cannot be trimmed up so they can’t enter very shallow water.
Watch this video on inboard engines
How to choose inboards vs. sterndrives
The choice between inboard and sterndrive propulsion is mostly based on the type of boat and its uses. Day and water sports boats tend to have sterndrives while larger boats or tournament towing boats opt for inboards. A final note on sterndrive boats in the US: The American market has been moving away from sterndrive solutions for some time and most have been replaced by more powerful, quieter and economical outboards. Therefore, the better comparison discussion to have today is inboard vs outboard propulsion.
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