How Sailboat Engines Work: Powering Your Voyage

Sailboats have been around for thousands of years, and while smaller vessels like dinghies are often propelled by wind alone, it is now standard for sailboats to have engines. Engines are particularly useful for sailboats in congested marinas, where they can help with manoeuvring, and in windless conditions, where they can provide the necessary power to keep the boat moving. Engines can also be used in combination with sails to help stabilise a sailboat's motion and increase its speed.

Motorsailers: yachts with engines and sails that work independently

Motorsailers are a type of motor-powered sailing vessel, typically yachts, that can derive power from their sails or engines independently. This means that the yacht can be propelled by its sails or engine even in moderate winds or seas. Motorsailers usually have a sheltered steering station, likely in the form of a pilot house, with the emphasis on comfort and the ability to cruise long distances.

The capabilities of the engine and sails can be described as a ratio of sail-to-engine power, with a range of 30/70 to 70/30. A 30/70 ratio has a smaller sail plan and a larger engine, while a 70/30 ratio has a powerful rig under sail, despite the water and fuel tankage. Motorsailers often have variable-pitch propellers to mitigate drag caused by their large diameter.

Motorsailers typically have a multi-masted split-rig sail plan, such as a ketch, yawl, or schooner, which provides ease of sail handling and better balance in heavy weather. They offer advantages over conventional auxiliary sailboats, including comfort, reliable passage-making, and ease of short-handed sailing.

The decision to include an engine in a sailboat depends on factors such as the size, intended use, and age of the vessel. While small sailboats like a Hobbie Cat or Sunfish rely solely on wind power, larger boats often require an engine for manoeuvrability in tight anchorages and harbours. Inboard and outboard engines are the two main types of motors found in sailboats, with diesel engines being the most popular choice due to their reliability and power-to-weight ratio.

Inboard engines are installed within the sailboat and are typically water-cooled, while outboard motors are clamped to the transom or back of the boat and can be raised or lowered as needed. Electric outboard motors are lightweight and can be stashed below deck, but they may not have the power to move larger sailing yachts at high speeds for extended periods.

Inboard vs outboard: inboard engines are inside the boat, while outboard engines are attached to the back

Sailboats have been around for thousands of years, and only recently has it become standard for them to have engines. Small sailboats such as a Hobie Cat or Sunfish don't have a motor and are propelled solely by the wind. However, as boats grow in size, the necessity of a motor becomes clear for most sailors.

There are two types of sailboat motors: inboard and outboard. Inboard engines are inside the boat, while outboard engines are attached to the back. Here is a more detailed look at the differences between the two:

Inboard Engines

Inboard engines are installed within the sailboat and are not visible from the outside, except for the water coming out of the exhaust at the stern (back) of the boat. Inboard motors are generally water-cooled, and the wastewater exits the boat with the exhaust. The propeller operates on a shaft that runs through the hull of the sailboat and connects to the motor. Controls for the motor are typically located in the cockpit.

Inboard engines offer several advantages. Most inboards are diesel, which are generally more reliable, cost less to run and maintain, and eliminate the hazards of gasoline. Well-maintained marine diesel engines can last for decades. Inboard engines are also out of sight, preserving the boat's aesthetic appeal. They provide ballast and increase stability due to their low position in the hull. Inboard engines tend to have more electrical power and allow for more extensive systems and equipment for cruising. The propeller is also lower in the water, reducing the risk of cavitation in steep waves.

However, inboard engines have some disadvantages. They are heavier, making the boat slightly slower. Their installation in tight spaces often makes them difficult to work on. Replacing or overhauling an inboard engine can be very difficult and expensive, and it may require cutting through the deck or hull. Inboards also take up significant space inside the boat. Additionally, they require shaft packing where the propeller shaft exits the hull, increasing the risk of water leaking into the boat.

Outboard Engines

Outboard engines are attached to the transom (back) of the sailboat using a special motor mount. This mount allows the outboard motor to be raised or lowered as needed. Outboard motors are available in various horsepower ratings, and the appropriate horsepower is chosen based on the hull speed of the vessel. Both diesel and gasoline outboard motors are available, and they can be two-stroke or four-stroke configurations. The controls for the outboard motor may be located at the motor itself or installed in the cockpit.

Outboard engines offer several benefits. They are easily accessible for service and can be removed for repair or replacement. The motor can be tilted to lift the propeller out of the water, reducing drag when sailing and minimising the risk of entanglement with lines or debris. Newer four-stroke outboard engines are quiet and vibration-free. Outboard motors are generally cheaper than inboard engines.

However, outboard engines also have some drawbacks. Some people consider them less aesthetically pleasing than inboard engines. Because the propeller is not deep in the water, it may cavitate (spin without power) in steep waves. The fuel tank may be positioned awkwardly or dangerously, depending on the boat design. Older two-stroke outboard motors can be noisy and smoky. Additionally, an oversized outboard motor can make the sailboat unbalanced.

In summary, both inboard and outboard engines have their advantages and disadvantages. The choice between the two depends on various factors, including the size, intended use, and personal preferences for the sailboat.

Engine maintenance: engines are expensive to maintain and fuel

Engines are expensive to maintain and fuel. The cost of the engine, both in the initial outlay and maintenance, is significant. You can expect to pay several hundred dollars a year just to keep the engine running, and that's before you've factored in servicing and winterizing.

On top of that, you've got the cost of fuel. While sails need to be replaced and repaired, fuel is a much bigger consumable. The amount of fuel you'll need will depend on how thirsty your engine is. A 30-gallon tank for a 30-foot yacht is a good baseline, but you may also want to keep a couple of jerry cans of diesel as a backup.

If you're considering an electric motor, bear in mind that small motors need to be run at full power to move a sailing yacht at a reasonable speed, and a typical battery bank won't sustain greater horsepower for long. However, for short, slow journeys, such as in and out of the harbor, an electric outboard may be sufficient.

Diesel engines are the most popular choice among sailing boat owners due to their reliability and power-to-weight ratio. Diesel-electric propulsion is also an option, using an inboard diesel engine to generate electricity to charge batteries that drive the electric motor. This setup gives you the benefit of an electric drive without the drawbacks of batteries.

When it comes to choosing the right engine size, a good rule of thumb is to select an engine that will allow you to cruise at maximum hull speed plus a little extra for challenging conditions. This will ensure you can reach the maximum speed possible, even in rough seas.

The cost of retrofitting an engine to a sailboat is also something to consider. For an inboard engine between 6 and 80 kW, you can expect to pay between $4000 and $10000 for the engine, plus $3000 to $5000 for installation.

While engines come with ongoing costs, they provide safety and control, especially in congested marinas. They also give you the ability to move when there is no wind, so you're not left stranded in windless conditions.

Electric outboards: electric engines are stashed below deck and used when needed

Sailboats have had engines for a relatively short time in the long history of sailing vessels. Engines are used to power the sailboat when there is no wind or in tight anchorages and harbors. There are two types of engines for sailboats: inboard and outboard. Inboard engines are installed within the sailboat and are not visible from the outside. Outboard motors are attached to the back of the sailboat using a special motor mount.

Electric outboard motors are a type of engine that can be used to power sailboats. Electric outboards are stashed below deck and used when needed. They are compact, efficient, and reliable. Electric motors are in constant 'standby' mode and can be engaged at any time for instant forward or reverse propulsion. They can achieve instant torque with Electromotive Force, while internal combustion engines need to build RPMs gradually. Electric motors also do not produce exhaust emissions, and they produce greatly reduced noise, vibration, and maintenance requirements compared to traditional engines.

Electric outboard motors come in a variety of horsepower options, from 5 HP to 50 HP. They can be used on boats of all shapes and sizes. Electric outboard motors are available from a number of companies, including Elco Motor Yachts and Torqeedo. Elco Motor Yachts offers a range of electric outboard motors with horsepower ranging from 5 HP to 50 HP. Torqeedo offers electric motors for dinghies and small boats, as well as larger commercial vessels.

In addition to the benefits of electric outboard motors themselves, there are also battery options that can extend the range of these motors. Lithium-Ion batteries have the highest storage capacity, high effective current delivery, high charge capacity resiliency, and a wide temperature range performance. DC generators have the advantage of rapid recharging capability, while AC generators are smaller and more portable. Solar panels can also be used to recharge batteries.

Engine sizing: bigger boats need bigger engines

The size of a sailboat's engine depends on several factors, including the size and weight of the boat, its intended use, and the level of sailing experience of the crew. While some small sailboats may not have an engine and rely solely on wind propulsion, larger boats typically require an engine for manoeuvring in tight anchorages and harbours, and for travelling in windless conditions.

When it comes to engine sizing, bigger boats generally need bigger engines. The horsepower of an engine significantly impacts the boat's overall performance, including its top speed, acceleration, and ability to handle challenging conditions such as strong currents or choppy waters. Heavier boats require more powerful engines to reach planing speed, where the hull rises and glides on top of the water. As a general guideline, small boats under 16 feet typically require 30-50 horsepower, while medium-sized boats between 16 and 20 feet may need 50-150 horsepower. Large boats, ranging from 20 to 30 feet, often require 150-300 horsepower, and extra-large boats exceeding 30 feet can demand up to 1000+ horsepower.

It is important to consider the boat's fully loaded weight, including passengers and gear, when determining the appropriate engine size. Additionally, the hull design can influence power needs. For example, a v-hull is more efficient at splitting water than a flat bottom, potentially requiring less horsepower.

When choosing an engine for a larger sailboat, it is advisable to opt for an engine at the upper end of the boat's recommended capacity. This is especially important if the boat is intended for high-performance needs or ocean use. A more powerful engine provides better handling, improved control in rough weather, and enhanced security in challenging conditions.

While bigger engines typically consume more fuel, it is important to consider the strain on an underpowered engine. A smaller engine may struggle to power a large boat, leading to increased fuel consumption and more frequent repairs. Therefore, it is generally recommended to choose an engine with slightly more horsepower than the minimum requirement to ensure optimal performance and prolong engine life.

In addition to horsepower, other factors such as engine type, configuration, fuel efficiency, and maintenance requirements should also be considered when sizing an engine for a larger sailboat. It is crucial to balance performance, practicality, and budget to find the right engine for the boat's specific needs.

Frequently asked questions