Choosing an Inboard or Outboard Engine

You should consider many different questions when deciding what kind of sailboat is best for you.

If you are looking for a large daysailer or a small cruising sailboat, you may be choosing between sailboats that have an inboard engine and those having an outboard motor. Each offers certain advantages.

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Inboard vs Outboard Engine

Inboard and Outboard Engine Sailboats — Tom Lochhaas

Many aspects of inboards and outboards are similar. Fuel consumption does not vary hugely, and parts and mechanics are equally available for both when a problem occurs. Standard maintenance can easily be done by owners of both. Operating controls are similar. Many sailboat outboards, like inboards, are battery started and use alternators to return power to the batteries and supply the boat's needs.

Yet there are many other important differences.

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What Engine Was the Boat Built For?

Catboat Sailboats Outboard and Inboard — Tom Lochhaas

The huge majority of sailboats large enough to have a motor were built for either an inboard or an outboard, so you'll usually be choosing between boats that already have one or the other installed. Yet you may still need to decide between Boat A with one type and similar Boat B with the other. The two catboats shown in these photos, for example, are of roughly the same size, and one has an outboard while the other has an inboard.

As boats age, however, engines sometimes need to be replaced, and sometimes an owner replaces the original inboard engine with an outboard. (This virtually never happens in the reverse, however, as boats built for outboards do not have the room or structural support for an inboard engine to be later added.)

If you're looking at a sailboat converted from an inboard engine to an outboard, be observant when you take the boat for its sea trials. With a very large outboard motor, for example, the boat may be imbalanced by having that weight far astern and may "squat" in the water and not sail as well. Also ensure that the fuel tank was properly installed so that leaks or fumes cannot collect belowdecks and create an explosion risk.

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Benefits and Disadvantages of Inboards and Outboards

Sailboats with Inboard and Outboard Engines — Tom Lochhaas

Inboard engines and outboard motors each have their own benefits but also disadvantages. If choosing between comparable boats with different engine types, be sure you have considered these differences:

Advantages of an Inboard Engine

Most inboards are diesels, which are generally more reliable, cost less to run and maintain, and eliminate the hazards of gasoline
A marine diesel engine that has been well maintained can last most of a lifetime (lots of 30+-year-old diesels still running well on sailboats)
The engine's weight is low in the hull, contributing positively as ballast for increased stability
An inborn engine is out of sight and out of mind – and does not disturb the beauty of the boat's appearance
As only a very general rule, most sailboats with inborn engines have more electrical power and more extensive systems and equipment installed for cruising
The prop is lower in the water and less likely to cavitate in steep waves

Disadvantages of an Inboard Engine

Inboards are heavier and make the boat a little slower
Inboards are typically mounted in tight spaces and are often difficult to work on
It is very difficult and expensive to remove an inboard engine for overhaul or replacement, and sometimes impossible without cutting through fiberglass
Replacing an inboard with a new inboard is more expensive than with an outboard of comparable size
Inboards take up a lot of space below
Inboard engines require shaft packing where the prop shaft exits the hull, increasing the risk of water leaking into the boat (even - rarely - fatally)

Advantages of an Outboard Motor

Accessibility makes it easy to service the motor
An outboard can be removed much more easily for repair or replacement
In most cases the motor can be raised or tilted to get the prop out of the water, producing less drag when sailing – and reducing the risk of entangling lines or debris in the water
Depending on the mounting, it may be possible to turn the motor for increased steering capability in tight places
Newer four-stroke engines are quiet and vibration-free
Outboard motors are cheaper than inboard engines

Need a new outboard motor for your small sailboat? Check out the great new propane-powered outboards from Lehr.

Disadvantages of an Outboard Motor

To many eyes, an outboard makes sailboats look ugly
Because the prop is not deep in the water, it may cavitate (spin without power) when the stern rises up in steep waves
Unless the boat was well designed to prevent this, the gasoline fuel tank may be positioned awkwardly or even dangerously
Older two-stroke motors can be noisy and smoky
An oversized outboard can make the sailboat unbalanced

As in other decisions when shopping for a sailboat, the best type of motor depends mostly on your preferred uses of the boat. The same is true when comparing fixed keel and centerboard sailboats or sloops and ketches.

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Outboard Motor Bracket

Sailboat Outboard Bracket — Tom Lochhaas

Outboard motors are typically mounted on sailboats via separate bracket, not clamped on the transom as on most powerboats. Check the bracket carefully in any boat you are considering. It needs to be sturdy and mounted securely, and it should be rated for the outboard motor's weight. Newer four-strokes are heavier than older two-strokes, so if you (or the previous owner) replace the outboard, you need to make sure the bracket is still appropriate.

Many outboard brackets, like the one shown here, can be moved up and down to raise and lower the motor. This is a beneficial function because the mounting does not always provide enough room for all outboards to be tilted forward on their own mounts. Measure this carefully if you're buying a sailboat with an installed bracket but no motor until you buy your own.

A final word: some sailboat builders have resolved the debate between inboards and outboards by designing the cockpit and hull with a well in which an outboard is mounted. In this case the outboard functions like an inboard with many of the advantages of both. While this design is a compromise in some respects, it works well on many boats. The biggest disadvantage is usually that because the well has fixed dimensions, it is impossible to install a larger outboard. Since newer four-strokes are larger than two-strokes of similar horsepower, it can be impossible in some cases to upgrade from an older two-stroke outboard to a four-stroke with greater or even comparable horsepower.