Weekend Cruising: Small Diesel Engine Boat Recommendations

When it comes to choosing a small diesel engine for your boat, there are several factors to consider. Firstly, it's important to determine your power needs and sea-trial models with different power options to find the best fit. Engine weight, size, and accessibility for service are also key considerations. In addition, the type of engine – gasoline or diesel – will impact your decision, with diesel engines offering improved fuel efficiency and reduced emissions thanks to advancements in technology. When it comes to specific engine recommendations, brands like Yanmar, Beta, Nanni, Volvo, and Cummins offer a range of reliable and efficient options for small boats. It's also worth noting that the size and weight of your boat will play a significant role in determining the most suitable engine, as will your intended use and cruising speed.

Engine weight and size

When selecting a diesel engine, it is essential to evaluate the engine's weight and how it affects the boat's overall performance. Engine weight is a critical factor in the power-to-weight ratio, which influences the boat's speed and manoeuvrability. A heavier engine may require a larger and more stable boat to maintain balance and prevent issues like wallowing. Therefore, it is crucial to match the engine weight to the boat's size and design.

In addition to weight, the physical dimensions of the engine are also important. When repowering an existing boat, it is crucial to choose an engine that fits within the available space. Engine size also determines the ease of access to service points for maintenance and repairs. It is essential to ensure that filters, impellers, and other critical components can be reached and serviced without difficulty.

When considering engine weight and size, it is worth noting that modern diesel engines have become lighter and more compact while delivering improved performance. Technological advancements have led to cleaner, more efficient, and more reliable engines. Additionally, the adoption of common rail injection systems and electronic controls has enhanced power and fuel efficiency.

In summary, engine weight and size are critical factors when choosing a diesel engine for a boat. The weight impacts the power-to-weight ratio and overall performance, while the physical dimensions determine the ease of installation and access to service points. It is essential to strike a balance between engine weight and size to ensure optimal performance, efficiency, and ease of maintenance.

Fuel efficiency

Firstly, it's important to understand that the amount of horsepower required to move a boat depends on various factors such as boat size, weight, shape, trim, bottom condition, running gear design, and underwater drag. External factors like wind, waves, and current can also impact the amount of horsepower needed. Therefore, when considering fuel efficiency, it's crucial to think about the specific circumstances in which the boat will be operated.

In general, marine diesel engines with higher horsepower tend to consume more fuel. For example, a 1,000-horsepower engine may burn around 40 gallons of fuel per hour at wide-open throttle, while a 500-horsepower engine might burn approximately half that amount. However, it's important to note that the relationship between horsepower and fuel consumption is not linear, and other factors can influence fuel efficiency.

The design and condition of the propeller and running gear are crucial for fuel efficiency. A well-maintained and properly sized propeller can significantly improve fuel economy, as it reduces the amount of power needed to propel the boat through the water. Regular maintenance of the running gear, including the propeller, shaft, and bearings, is essential to ensure optimal fuel efficiency.

The weight of the engine itself also plays a role in fuel efficiency. Heavier engines require more power to move, which can lead to increased fuel consumption. Additionally, the physical dimensions of the engine and the motor mount footprint should be considered, especially when repowering an existing boat.

The advancement of technology has led to significant improvements in fuel efficiency for marine diesel engines. Modern engines, such as those with common rail fuel injection systems, often offer better fuel economy than their older counterparts. For example, common rail injection technology allows for more precise fuel injection, resulting in improved combustion and reduced fuel consumption. However, these systems may be more susceptible to poor-quality fuel and may require specialized tools and training for maintenance.

When comparing fuel efficiency across different engines, it's important to consider the engine's operating speed. Engines with higher operating speeds, typically measured in revolutions per minute (RPM), tend to consume more fuel. Therefore, it's crucial to compare fuel consumption at similar RPMs to get an accurate understanding of an engine's fuel efficiency.

Finally, it's worth noting that, in some cases, running a single engine on a twin-engine boat may provide slightly better fuel economy. However, this depends on various factors, and the overall difference in fuel consumption is often negligible. Additionally, running a single engine can have other drawbacks, such as increased drag and the need for corrective rudder action.

Engine maintenance

Small diesel engines are remarkably reliable, even in harsh saltwater environments. However, their high level of reliability can only be sustained if the engine is properly maintained. Here are some tips to keep your small diesel engine in good condition:

Regular Maintenance and Checks

• Follow a regular maintenance schedule and look for problems proactively.
• Check the engine's exterior and fuel level before every start, if possible.
• Check for water flow from the exhaust immediately after engine start.
• Refer to the operating manual for periodic maintenance tables and recommendations.
• Change the secondary fuel filter regularly.
• Drain the fuel/water separator and replace fuel filters as per the manufacturer's guidelines.
• Check and replace the seawater pump impeller as per the maintenance schedule.
• Change the engine oil and oil filter at the recommended intervals.

Troubleshooting and Problem Prevention

• Listen to your engine and exhaust for any unusual sounds or smoke, which can indicate issues with cylinders, cooling systems, or fuel combustion.
• Check the cranking voltage and alternator output to ensure the battery and electrical connections are in good condition.
• Inspect your fuel tank for water and contamination regularly. Use a hand pump to draw a sample from the bottom of the tank and check for water, dirt, or bacteria.
• Fit an exhaust temperature sensor to monitor cooling water flow and prevent overheating.
• Keep an eye on your marine engine instruments and mark normal value ranges to easily spot potential issues.
• Check for black dust around the alternator or water pump drive belts, which may indicate accelerated belt wear due to tension, pulley alignment, or rust issues.
• Keep spare parts on board, such as drive belts, filters, and impellers, in case of unexpected issues.

Engine brand and service availability

When it comes to engine brand and service availability, there are several factors to consider. Firstly, it is important to determine the power requirements for your boat, as this will influence the engine brand and model that would be most suitable. Different brands offer different power outputs, so selecting an engine that meets your specific needs is crucial. Additionally, the weight and size of the engine should be taken into account, especially if you are repowering an existing boat. It is essential to ensure that the engine fits within the available space and that you have access to service points for maintenance.

Another critical factor is the availability of professional service and parts near your cruising waters. Opt for a brand with a strong dealer network and a good reputation for customer service. This will ensure that you can easily access maintenance and repairs when needed. Some brands with extensive dealer networks include Yanmar, Volvo Penta, Beta Marine, and Nanni. Yanmar and Volvo Penta are widely recognised brands in the sailing arena, known for their reliable engines. Beta Marine, a British company, offers engines based on the Kubota block and provides a five-year warranty for recreational boats, along with a global dealer network. Nanni, a French-Italian brand, has a strong global presence as well, although parts may be harder to find in the United States.

When considering engine brands, it is worth noting that some companies simply repackage and rebrand base engines from other manufacturers. For example, Volvo Penta uses Perkins engines for their small engines, while Perkins uses Kubota engines. Therefore, it is important to do your research and understand the underlying engine manufacturer to make an informed decision.

In terms of specific engine recommendations, for a wooden deep keel boat around 22 feet long and over two tons, Yanmar, Beta, Nanni, and Volvo are all popular choices. Yanmar has a strong reputation and offers a range of power options. Beta engines are known for their reliability, good value, and compact design. Nanni engines are also well-regarded, with indirect mechanical fuel injection and water-cooled exhaust manifolds. Volvo Penta engines are commonly used and offer a range of power outputs to suit different needs.

When making your decision, consider factors such as cost, reliability, fuel economy, and the availability of spares and servicing. Additionally, pay attention to features like heat exchangers and warning sirens, which may be important for your specific use case.

Engine power

When it comes to engine power, there are several factors to consider when choosing a small diesel engine for your boat. Here are some key points to keep in mind:

• Horsepower: The amount of horsepower you need will depend on the size and weight of your boat, as well as your desired speed. It's important to strike a balance between having enough power to move your boat efficiently and not overspending on more horsepower than you need.
• Fuel Efficiency: Diesel engines are known for their fuel efficiency, but it's still important to consider the fuel consumption rates of different engines. This is especially important if you plan to use your boat for extended periods or in remote locations where refuelling may be difficult.
• Emissions: With tighter regulations on emissions, modern diesel engines produce significantly less harmful emissions than their older counterparts. If you're environmentally conscious or plan to operate your boat in areas with strict emissions regulations, look for engines that comply with standards such as the Recreational Craft Directive (RCD) and the EPA Tier 3 requirements.
• Common Rail vs Mechanical Injection: Common rail injection systems offer benefits in terms of power and fuel consumption, but they rely on electronic control units and are more susceptible to poor-quality fuel. Mechanical injection systems, on the other hand, are simpler and easier to maintain, but may not offer the same level of performance.
• Engine Weight and Size: The weight and size of the engine are important considerations, especially if you're repowering an existing boat. Make sure to choose an engine that fits within the available space and doesn't add too much weight, as this can affect the boat's performance and fuel efficiency.
• Service and Parts Availability: When choosing a diesel engine, it's crucial to consider the availability of qualified service professionals and spare parts. Opt for well-known brands with extensive dealer networks and good aftermarket support to ensure that you can get the support you need, especially if you plan to cruise in remote locations.
• Alternator Output: If you plan to rely on your engine for battery charging, pay attention to the alternator output. Modern engines often have more powerful alternators to meet the increasing electrical demands on board.
• Single vs Twin Engines: If you're considering a twin-engine setup, keep in mind that running just one engine at a time may not provide significant fuel savings, especially if your boat is well-powered for its size. Running a single engine can also result in increased drag and the need for corrective rudder action.
• Engine Brand: Popular brands of small diesel engines for boats include Yanmar, Volvo Penta, Beta Marine, Nanni, Solé, Cummins, Caterpillar, Cox, MAN, MTU, Scania, and Lombardini. Each brand has its own strengths and weaknesses, so be sure to research their features and suitability for your specific needs.

Frequently asked questions