Marine engines are the vessel’s beating heart. They produce hot water and the electricity required to spin radars, grind winches, and pull anchors. Modern marine engines are small and dependable, but they only run for a few hours at a time, which can lead to ‘standing’ issues. A typical boat will only log roughly 30 engine hours every season, which is less than your diesel car will do in a fortnight. In addition, it is rare for a marine engine to get damaged. However, they tend to corrode and need proper maintenance. It’s rare these days to come across a bad-quality marine engine. In this article, I will give some information about marine engines as well as which ones are the most reliable for sailboats. Follow me!

Characteristics of Marine Engines for Boats and Sailboats

Because the market for new marine engines is so small in comparison to car engines, there aren’t so many companies that design engines with less than 300 horsepower from the ground up. Bukh, Yanmar, and Steyr are notable companies, as they build their own basic engines using in-house components. The others are tried-and-true industrial or automotive blocks from Kubota, Mitsubishi, Volvo, and Toyota that have been ‘dressed’ with a marinized cooling system to enable them to run afloat. The quality of the marinization will have a significant impact on the engine’s reliability.

If you’re looking for the best reliable marine engines then you’re either buying a new boat and need to choose an engine, or you want to replace or enhance the one you have. In either case, you’ll be investing not only in the engine but also in its continued role in your enjoyment and safety. This means you should seek features like quick start-up, quiet operation, outstanding fuel economy, total dependability, and low-cost spares and maintenance.

Engine Power

Any motor (inboard or outboard) installed on a sailboat is an important tool that aids maneuvering. Although some competent sailors can sail efficiently without the use of power, many harbors have regulations that either prohibit the use of full sails or simply don’t allow for enough maneuvering space. And, note that docking is becoming easier with a motor that has both forward and reverse gears. While there is no exact relationship between boat length and total weight there is a general rule of thumb. For boats, up to 20ft 1-4 horsepower is a must while for boats between 20 and 30ft, 4-18 horsepower is great. Also, for boats between 30 and 40ft, the 18-34 horsepower is the way to go.

Keep in mind that in order to get your boat moving, you just need a small amount of power. However, when you’re dealing with fast currents, waves, and strong headwinds, you’ll be glad you have plenty of reserve horsepower. You should allow 3 horsepower per tonne of displacement, or 1 horsepower per foot of waterline length, as a general rule. This is general guidance with many limitations, but boat manufacturers typically over-specify the engines so that they run at lower speeds and be more economical.

When determining how much horsepower you want, there are a few factors to consider. One of the most important criteria is your location and the type of conditions you intend to sail in. Heavy seas and strong winds, which are typical of open ocean sailing, may put extra strain on your engine and, in some situations, overpower it. But, a heavier-than-needed engine would add unneeded weight when racing. So, consider buying an engine that can withstand a lot of use if you plan on sailing long distances.

How Much HP Do you Need?

The amount of power you require is proportional to the displacement of your boat’s hull. So 1 HP every 550 lb displacement and 4 HP per 2200 lb displacement. The amount of horsepower required to reach the maximum hull speed is denoted by HP. This is in ideal circumstances. You must additionally account for propellor size if you want to get it exactly properly. So, you can divide the boat’s displacement (in lbs) by 550 to find the amount of horsepower in order to efficiently propel a sailboat. Note that for most sailboats, you don’t need more than 30HP.

Generally, you need more HP for catamarans and larger boats (regardless of size) that necessitate more power.
Note that engine weight and an extra step of compression in a 4-stroke engine results in less output. You will also need more HP if you have a small propeller as it tends to displace less water. If you’re sailing in the ocean, cover large distances, and deal with rough weather you will need a more powerful engine. And, gas engines have a substantially lower compression rate than diesel engines.

On the other hand, you will need less HP if you have a single hull fiberglass sailboat and bigger props as they displace more water. If you’re an occasional sailor and cover small distances you will need less HP. In addition, 2-stroke engines that are lightweight and have higher torque require less HP. And, less HP for diesel engines because they have a bigger compression rate.

Engine Size

There are a few reasons why getting the appropriate engine size is important. First and foremost, smaller engines are less expensive, thus you save money on the engine. Second, smaller engines consume far less gasoline, resulting in cost savings. Finally, smaller engines are less expensive to maintain. However, there are a few benefits to upgrading to a larger engine. More control equals more power thus it’s easier to stop the boat, in case you need to.

A bigger boat doesn’t always imply having a bigger motor. Meaning that a small power plant can be more effective than a larger one, despite varying ratings for different classes of boats. An outboard motor, on the other hand, can easily overpower a small boat and produce dangerous situations at high speeds. In general, there are differences when it comes to the engines of sailboats and motorboats.

Your engine’s physical size is a crucial issue that is closely tied to the design of your boat. Note that the engine consists of three parts. The powerhead houses the engine. The exhaust system in the midsection and the lower unit submerges when in use.

When choosing a motor, the shaft length is an important design feature to consider. A propeller with a shaft that is too short will not submerge in water, but a shaft that is too long will stretch the propellers too far. This will not only reduce the efficiency of your engine, but it will also add extra drag. When comparing models, keep your transom length in mind. When not in use, an outboard motor should be stowed in the upright position. Some of the larger motors have an automated switch that allows them to be raised out of the water, but others must be secured manually.

Two-Stroke vs Four-Stroke Engine?

Outboard engines are either two-stroke or four-stroke, with the four-strokes gaining popularity in recent years for various reasons. They’re quieter, consume less gasoline, and operate cleaner. Each power stroke in a four-stroke engine causes the piston to reciprocate four times inside the cylinder. In other words, each time the fuel combusts. Engineers reduce the length of time the intake and exhaust valves are both open by carefully engineering the camshaft. This significantly reduces the amount of unburned gasoline that departs with the exhaust stream. What’s the end result? Emissions are reduced and there are cost savings.

However, in the five-horsepower category, four-stroke engines are around 20% heavier than two-stroke engines with the same horsepower. Four-stroke engines are also more expensive, although the enhanced technology may be well worth the extra expense. You’ll want a two-stroke engine if you’re trying to save weight and money. However, if you believe you can reduce weight in other ways, a clean, quiet four-stroke without the trouble of mixing fuel could be the solution. Manufacturers are also being pushed toward four-stroke engines by environmental laws. This is because emission control standards are met by four-stroke engines.

Marinization

The standard of marinization is a key role since corrosion kills engines faster than any other sort of misuse, including unclean fuel. The heat exchanger is the most important component here. When the temperature difference between the engine and the outside water is modest, as it is when cruising in the tropics, efficiency is critical. Meaning that you’ll want to use high-quality, corrosion-resistant components that won’t need to be replaced. When looking for a new engine, you should also ask to see the spare parts price list. It’s pointless to buy a low-cost engine if the impeller is going to set you back a small fortune.

Drive Train Considerations

It’s important to note that the drive train will have an impact on the efficiency of your engine. Some owners choose to totally reposition the engine during repowering to free up more space in the boat. Switching from shaft to saildrive is another possibility. Saildrives are popular because they are simple to install from the standpoint of the boat builder. The entire unit – engine and transmission – is dropped into a specially-made cradle that is glassed into the bilge through a single large hole in the hull. And, the sea is kept out by a big rubber gaiter. The propeller works at right angles to the water, so no thrust is lost downwards, making it more efficient than a typical shaft drive. As the drive is more forward, there is usually less ‘paddle wheel’ impact, but the less prop-wash effect on the more distant rudder.

Most Reliable Marine Engines for Boats

Caterpillar C12.9 Marine Diesel Engine

The C12.9 did successful testing in test cells when it comes to reliability. The engine passed over 13,000 endurance hours on the water and proved its efficiency and durability. This engine has a high power density, quick acceleration, and little noise. The C12.9 received great grades for minimal noise, fast transient response, and available power throughout its testing. The C12.9 is available in two power ratings: 850 mhp at 2,300 rpm and 1,000 mhp at 2,300 rpm, both electronically controlled.

Mercury 75/90/115

Mercury introduced a new 2.1-liter outboard engine in 75, 90, and 115 horsepower models in 2015. These engines have close to the greatest displacement in their class while maintaining a low weight. In fact, at 359 pounds, it weighs 40 pounds less than the older 1.7-liter Mercury models. These engines perform smoothly, and Mercury claims that 17,000 hours of testing went into designing these outboards.

Cummins QSB 6.7

In the sport-fishing industry, the new Cummins Quantum Series QSB 6.7 with 550 horsepower is the most popular output. Cummins concentrates on noise reduction and has achieved an 80 percent decrease at idle thanks to engineering changes in their high-pressure common-rail fuel system, which is based on an in-line six-cylinder block with a new 24-valve cylinder head. This also contributes significantly to the reduction of smoke. Walker AirSep air filters are now standard, and they’re designed to reduce noise at the turbos’ air intake. The QSB 6.7 is a Tier 3 compliant power plant with a dry weight of 1,450 pounds that can be used in a variety of applications.

Cummins QSL 9

Cummins QSL engines are designed and built to provide heavy-duty performance in a variety of industries. In addition, the QSL series has superior fuel economy, enhanced cold starting capability, and produces less noise than its predecessors. The QSL9-G5 is an air-cooled turbocharged engine that is currently produced in India. The 6 cylinder engine is available in 50 Hz or 60 Hz versions, making it a versatile engine. A common-rail fuel injection system enhances engine performance, and the engine has four valves per cylinder for increased power. Lastly, note that for long-distance cruising, the fuel efficiency is excellent.

Mercury 4-stroke 3.4L V-6 AND 4.6L V-8S

The engine is available in naturally aspirated versions with outputs ranging from 175 to 300 horsepower. These are the lightest versions in their class, with Adaptive Speed Control. This is in order to keep RPM independent of load or wave conditions. The V-6 was the first of these engines to be released in 2018, and the V8 followed quickly. Mercury began supercharging these engines in 2019 to generate new Verado variants with up to 400 horsepower, extending the line even further. It’s tough to say how well these will hold up over time, but early reports from customers indicate that the models have proven to be quite reliable.

MAN R6-730 & R6-800 

With the demand for compact, space-saving engines, MAN’s in-line six-cylinder engines with horsepower outputs of 730 hp and 800 hp at 2,300 rpm are among the best engines. The R6-730 generates 730 horsepower for quick acceleration from low revolutions per minute engine speeds. This is thanks to a common-rail fuel arrangement that produces maximum torque in the 1,200rpm range. The R6-730 has a tempting horsepower-to-weight ratio for both re-powers and new builds, weighing in at around 2,870 pounds. The R6-730 does not require an external after-treatment system to meet Tier 3 emission compliance due to proven optimization of the internal combustion system.

Volvo Penta D2-50 Diesel Engine

Between the 28hp D1 and the 50hp D2, which are available in both shaft and saildrive configurations, Volvo has an odd gap in their engine lineup. The 3,000rpm of the D2 marine diesel engines is very common for this power rating. Slower rotation produces less noise and vibration in general. An inline injection is used in both series, as is the MDI electronic interface, which has had reliability issues in the past. The interface, on the other hand, makes getting NMEA data out of the engine and into your instrument network a breeze. It also makes a wide variety of stylish remote displays available. The D2 engine, however, will not operate with Volvo’s ergonomic computerized controls. Only EVC marine diesel engines with common rail injection are compatible with them.

Volvo D13-900 

The Volvo D13-900 is an in-line six with 900 horsepower that can be utilized as a conventional drive package or in conjunction with an IPS pod-drive power unit. Volvo has certainly made an impact in the maritime sector with this technology, with over 17,000 IPS systems on the water. The D-13 has a strong block with ladder-frame construction, high-pressure unit injection, and twin turbochargers with charge-air coolers, weighing in at 3,439 pounds. Volvo’s electronic control system’s engine management combines low fuel consumption and emissions with reduced vibration and noise, exceeding Tier 3 regulations.

MTU 16 V 2000 M96 Diesel Engine

The M96 is a 16-cylinder V engine that produces 2,600 horsepower at 2,300 rpm and comes with a new fuel-injection system. It also has three sequential turbochargers for improved acceleration and fuel economy. The M96 is EPA and IMO Tier 3 compliant thanks to the company’s SCR in-engine exhaust-gas treatment. The M96 is a smokeless, silent power engine with reduced vibration that is managed electronically. With the recent debut of the 92 Viking, the 2,600 hp M96’s performance qualities stand out, with the enclosed bridge variant reaching a top-end speed of 36 knots.

Yanmar 3JH40

This very popular, award-winning engine debuted in 2018 with a power output of 40hp. Its main feature is Yanmar’s common rail injection system efficiently reduces smoke and odors to almost nothing. This is owing to the diesel fuel’s more complete combustion when injected under high pressure. It also spins at a low 3,000rpm, which makes it quieter and decreases vibration than faster-spinning engines. For its engines, Yanmar has created a set of digital controls. Meaning that the VC10 and VC20 electronic throttles send data to the network, such as engine load.

Beta 43

Beta Marine diesel engines are built on a sturdy Kubota block and offer low-cost and excellent performance. They have a unique red color and come with a variety of installation options. This makes them ideal for repowering in confined spaces. This is a typical mechanical engine with very little electrical gimmickry, despite the fact that the design is always being refined. For its size, it has a lot of mid-range torque. Although an NMEA2000 converter is available to transfer some engine data into the network, the typical control panels are firmly analog. Also, a new digital display panel with a standard loom input and NMEA 2000 output is now available. These are good engines that are sold all around the world since they are reliable, have a lot of spare parts, and are easy to service.

Caterpillar C8.7

Caterpillar introduces its new C8.7, a six-cylinder in-line engine that replaces the C9. The C8.7 produces 650 horsepower at 2,300 rpm and weighs 2,295 pounds dry. This is thanks to a new common-rail fuel-injection system and air system. To get the boat up to speed without lagging before the turbocharger engages, the new fuel system employs a radial belt-driven supercharger in conjunction with standard turbochargers. Once up to speed, the turbo takes over for boost, and the supercharger is disengaged by an electromagnetic clutch. While remaining EPA Tier 3 compliant, this redesign minimizes smoke and provides substantial low-end torque and fuel economy. The C8.7 is well-suited to conventional drives, but it’s also designed to work with Caterpillar’s recently announced pod propulsion systems.

Solé Mini-44

Solé provides a wide range of diesel marine engines, and the Mini-44 is great for boats with a length of 32 to 39ft. This is the company’s smallest four-cylinder engine, which offers quieter operation but higher fuel consumption at the highest speeds. Despite its 42 horsepower rating, it has a lesser capacity and must work harder to accomplish it. As a result, it performs better than 38hp models. It’s a fully mechanical engine that uses cam-driven indirect fuel injection to create adequate torque in the mid-range.

The Mini-44 is an extremely versatile engine with several variations, including saildrive fittings, and an astounding range of gears. The engine’s analog data can be converted into digital signals for your NMEA 2000 network using a very expensive converter. The control panel options, however, remain decidedly analog, despite their beautiful design.

The Bottom Line

While sailing does not necessitate the use of an engine, it is a practical addition that may substantially enhance your time on the sea. Being patient and spending time searching for reliable marine engines will not only help you make the right choice but will also allow you to take advantage of a good deal. The most important criterion is to go beyond the engine’s original cost and consider the cost of spare parts, convenience of access, and maintenance. In addition, you should look for the service regime and global network of dealers in order to pick the right marine engine for your sailboat. Lastly, note that it’s improbable that the expense of a new engine installation will ever be recouped in the resale value of a used boat. Instead, you’re making a long-term investment in your enjoyment and safety.

I hope that this article will help you choose the right marine engine for your sailboat. And, that you have now understood the specs of a reliable marine engine. Wish you all safe & pleasant voyages!