While more established manufacturers offer several gasoline options, Cox Marine’s purpose-built diesel outboard brings new capabilities to the market.
The marine industry relies heavily on outboard engines to power vessels ranging from leisure boats to commercial and government fleets. Although gasoline brands dominate the market, Cox Marine has emerged as an innovator, producing the world’s only purpose-built diesel outboard. This development provides operators with greater durability, efficiency, and safety features not available in gasoline models.
But what sets Cox apart from other major manufacturers, and how is it transforming the industry?
Traditional 300-Horsepower Outboards: Proven Performance, but with Trade-Offs
In the 300-horsepower outboard segment, the market offers several well-established solutions, predominantly gasoline-powered, typically based on V6 or inline-six architectures. These engines deliver solid overall performance, thanks to advanced electronic controls and engine management systems designed to optimize power delivery and fuel consumption across the entire operating range.
In some cases, automotive-derived technologies are employed to enhance smoothness and improve fuel efficiency. Other solutions focus on mechanical innovations, such as dual-propeller systems, to increase traction and stability on larger hulls.
Noise and vibration reduction has been another area of focus, particularly to meet the needs of the leisure and cruising market.
Fuel efficiency is also among the most frequently highlighted strengths, especially when paired with electronic engine management systems that constantly monitor operating conditions. However, at sustained speeds or under heavy workloads, these advantages often diminish. Despite these technological evolutions, most market offerings remain tied to conventional solutions, generally aimed more at leisure users than at professional applications requiring long-range endurance and high resilience.
Cox Marine: Diesel Innovation for Specific Applications
Cox Marine has taken a different approach by developing the Cox Marine 300 V8, the only purpose-built high-power diesel outboard available today, and the Cox Marine 350 V8, the most powerful diesel outboard in the world. These engines address the specific needs of commercial, government, and military users, providing a robust alternative to traditional gasoline outboards. The Cox Marine V8 design philosophy prioritizes durability and efficiency, with every component engineered specifically for marine applications. This targeted approach ensures optimal performance without compromise.
The Diesel Advantage
The diesel configuration of the 300 and 350 V8s delivers greater torque at lower RPMs than gasoline engines, allowing for improved acceleration and load-carrying capacity. This results in higher fuel efficiency across all operating conditions, particularly beneficial for commercial operators managing fuel costs. Cox Marine’s diesel technology also produces lower CO2 emissions than gasoline counterparts, helping operators meet increasingly stringent environmental regulations.
Engineering of the Cox Marine diesel V8s emphasizes durability, resulting in a longer operational life compared to equivalent gasoline outboards, substantially reducing the total cost of ownership over the engine’s lifecycle.
Advanced Safety Features
The diesel operation of the Cox Marine V8 offers further safety benefits, which are particularly critical in commercial and military applications. Many commercial vessels, including government and military fleets, operate exclusively on diesel fuel. Using a single fuel source streamlines logistics and reduces operational risks, while simplifying maintenance and spare parts management.
The lower volatility of diesel compared to gasoline also creates a safer operating environment—an especially important factor for maritime operations in high-risk areas or conflict zones, where fuel safety is paramount.
The Future of Marine Propulsion
While established manufacturers continue to offer advanced gasoline solutions for a range of marine applications, Cox Marine has created a distinct proposition by developing the only purpose-built diesel outboard, delivering efficiency, durability, and advanced safety features.
As crew safety, environmental considerations, and operational efficiency become increasingly important in the marine sector, Cox Marine’s innovative approach provides operators with a diesel alternative that combines higher torque and greater durability with reduced emissions. The Cox Marine V8 meets the needs of commercial fleets, government operations, and high-performance leisure boating, demonstrating the viability of purpose-built diesel outboard technology. Its success highlights the potential for continued innovation in marine propulsion, particularly in meeting the constantly evolving demands of commercial and professional operators.
The demand for greater fuel savings, lower CO2 emissions, and higher performance is driving interest in diesel outboard engines. For those working in the commercial maritime sector, public services, or for leisure boat owners, diesel outboards offer several advantages over gasoline-powered alternatives, including higher efficiency and torque that allows for powerful thrust and acceleration. Switching to diesel also supports single-fuel strategies for larger fleets already running on diesel elsewhere.
In this article, we’ll cover everything you need to know about diesel outboard engines, including how they work, their benefits, limitations, key trends, and engine types.
What is a Diesel Outboard Engine?
A diesel outboard engine is a self-contained external combustion engine that integrates the powerhead, gearbox, and propeller, mounted on the stern (transom) of the vessel. While gasoline outboards are common in leisure boating, diesel outboards are typically used for heavier-duty, long-range, and commercial applications. Their high efficiency, durability, and fuel safety make them an attractive alternative.
Diesel has a higher energy density than gasoline, which is the key to superior fuel economy and a significant advantage over long distances, when fuel optimization is a priority. Diesel engines also deliver greater torque, making them ideal for towing loads, handling heavy vessels, and working in challenging marine conditions. Additionally, diesel is less flammable than gasoline, reducing the risk of fire in marine environments.
How Diesel Outboard Engines Work
One of the main advantages of a diesel outboard is greater fuel efficiency. This comes from “lean-burn” technology, which uses less fuel and more air to achieve the same performance as gasoline engines—typically delivering 30–35% better fuel economy. Lower fuel consumption also translates to reduced emissions, meeting stringent environmental regulations.
A diesel engine operates on the principle of compression ignition. Air is drawn into the combustion chamber and compressed at high pressure. Fuel is then injected directly into the chamber, where the compressed air is hot enough to ignite the fuel automatically, creating an explosion that pushes the piston downward and generates mechanical power. Exhaust gases are expelled, and the process repeats.
Back to Basics – The Different Types of Outboard Engines
Commercial outboard motors are available in various types, depending on fuel, power source, and intended application. These engines are widely used across transport and maritime operations. Below is an overview of the main types:
Gasoline:
Two-stroke engines: Simple design that mixes fuel and oil. Lightweight and high power-to-weight ratio. While powerful, efficient, and cheaper than diesel, they have higher fuel consumption and emissions, often failing to meet modern environmental standards.
Four-stroke engines: Separate oil and fuel systems, providing cleaner, more efficient combustion. Heavier and generally more expensive than two-strokes. The largest gasoline outboard reaches 600 HP.
Diesel:
Designed for heavy-duty use, diesel outboards provide more torque at lower RPMs. Diesel is more fuel-efficient and cost-effective in long-term operation, more durable, and better suited for heavy loads. The trade-offs include higher upfront costs, greater weight, more noise, and potentially more complex maintenance compared to gasoline. However, they are ideal for long-range travel and commercial operations requiring reliable performance.
Electric:
Powered by onboard batteries or hybrid systems, some electric outboards are completely emission-free—especially beneficial in areas with strict environmental regulations. They offer quiet operation, minimal maintenance, and growing range thanks to battery advancements. Currently, range and battery life remain limited, making them more suitable for tenders and small craft. The most powerful electric outboard today is 300 HP, with larger models emerging.
Liquefied Petroleum Gas (LPG/Propane):
An emerging alternative to gasoline. Propane burns cleaner than gasoline or diesel, reducing emissions. It’s more efficient, less costly to operate, and has a long shelf life. However, availability is limited in some regions, and range can be lower than gasoline or diesel.
Hybrids:
Combine a traditional internal combustion engine (gasoline or diesel) with an electric motor, offering flexibility between power sources. This provides zero-emission operation when needed, plus long-range capability with fuel. Still developing in marine applications due to higher upfront costs.
Jet Propulsion Outboards:
Powered by gasoline or diesel, these use a water jet instead of a propeller. Safer in shallow waters and near swimmers, offering excellent maneuverability. However, they’re less efficient than propeller-driven outboards and more prone to clogging with debris, leading to higher maintenance costs.
Diesel Outboards vs. Gasoline Outboards
Fuel Efficiency
Diesel has a higher energy density, making diesel outboards more fuel-efficient—especially at low speeds and over long distances. Gasoline outboards are less efficient, particularly under heavy loads, though they may be more efficient at higher speeds on smaller, lighter boats.
Performance
Diesel engines provide strong torque at low RPMs, making them reliable for moving heavy boats or towing loads. However, they usually have lower top speeds and slower acceleration compared to gasoline engines. Gasoline outboards generally offer faster acceleration and higher top speeds, ideal for small, agile boats.
Durability & Longevity
Diesel engines are built to withstand high stress and long operating hours, often outlasting gasoline engines—making them standard in commercial use. Gasoline engines, while durable, typically have a shorter lifespan under heavy use.
Safety
Diesel is less flammable than gasoline, reducing fire risk—a key advantage in commercial, military, or offshore operations. Gasoline is more volatile, though modern safety systems mitigate risks. Large-scale storage of gasoline also raises ATEX compliance concerns in Europe.
Single-Fuel Strategy
Many operators benefit from using diesel across fleets, simplifying storage, logistics, and supplier management.
Costs
Diesel outboards are more expensive upfront due to their robust construction, but lower fuel consumption and longer lifespan offset the initial cost. Gasoline outboards are cheaper initially but incur higher long-term running costs.
Environmental Impact
Diesel produces more particulate matter (PM) and NOx, but newer engines have reduced emissions. Because they burn less fuel overall, their carbon footprint can be lower. Modern four-stroke gasoline engines are relatively clean, though two-stroke models remain more polluting.
Maintenance
Diesel engines need less frequent servicing but can be costlier to repair when issues arise. Gasoline engines are simpler and cheaper to maintain, with more readily available parts, though they may require more frequent upkeep.
Diesel vs. Electric Outboards
Power & Performance Diesel: better suited for heavy-duty, long-range, commercial use, with high torque and endurance. Electric: quiet, instant torque, better for small boats and short-range trips. Advances in batteries are expanding their capabilities, but diesel still dominates for long-distance operations.
Efficiency & Fuel Diesel is fuel-efficient and ideal for long trips, but still reliant on fossil fuels. Electric is highly energy-efficient and has no fuel costs (other than charging), especially when paired with renewable energy sources.
Maintenance Diesel: requires oil changes, filter replacements, and fuel system servicing. Electric: simpler, fewer moving parts, very low maintenance, though battery replacement can be costly.
Environmental Impact Diesel emits CO2, NOx, and particulates, while electric outboards are zero-emission at the point of use. With renewable charging, electric can achieve near-zero carbon footprint.
Choosing the Best Diesel Outboard for Your Boat in 2025
When selecting a diesel outboard, consider:
Horsepower & torque: match engine size to vessel weight and workload.
Fuel consumption & range: ensure efficiency for long-distance operations.
Maintenance needs: choose a brand with strong service and parts support.
Environmental compliance: verify adherence to IMO and EPA standards.
Weight & compatibility: confirm your transom and hull design can handle added weight.
Trends Driving Innovation
With stricter environmental regulations, manufacturers are prioritizing reductions in NOx and particulate emissions to meet IMO Tier III and EPA standards. Electric and hybrid propulsion are emerging as alternatives, reducing underwater radiated noise (URN) and vibrations.
Manufacturers are focusing on developing sustainable, clean-combustion diesel outboards that meet evolving environmental standards while improving efficiency. For example, Cox Marine’s purpose-built high-performance V8 bi-turbo diesel delivers at least 30% better fuel economy, lower noise, and reduced emissions—while maintaining peak torque, making it ideal for commercial and leisure use. Hybrid diesel-electric outboards are also emerging as eco-friendly solutions, particularly valuable in coastal and protected marine areas.
The Future of Diesel Outboards
Diesel outboards remain an excellent choice for maritime businesses and public agencies prioritizing fuel efficiency, safety, and vessel durability. Despite higher upfront costs, their torque, fuel savings, and long lifespan justify the investment, especially for commercial operators seeking a single-fuel strategy.
Whether upgrading or installing new, diesel outboards provide reliable power across a wide range of marine applications. With ongoing technological advancements, the industry can expect even more efficient and environmentally friendly diesel outboards in the future.
The Cox Marine V8: 300 HP and 350 HP Diesel Outboards
Cox diesel outboards are the most effective alternative to gasoline outboards, offering several key advantages: up to 30% better fuel efficiency, significantly lower operating costs, support for single-fuel strategies, and improved onboard safety. Built to withstand the toughest marine conditions, Cox Marine engines comply with the strictest environmental standards and deliver reliable, long-lasting performance—from sportfishing to global commercial operations.
For the first time in the history of the America’s Cup, the all-female crew of Luna Rossa Prada Pirelli triumphed in the world’s most famous sailing competition. In the waters of Barcelona, the Italians wrote a new chapter in sailing history, defeating the British team “Athena Pathway” in the grand final of the Women’s America’s Cup.
Giulia Conti and Margherita Porro at the helm, with Giulia Fava and Maria Giubilei as trimmers, led Luna Rossa’s AC40 to triumph. The achievement began with a preliminary race and the semifinals, where the Italian sailors prevailed with 5 wins out of 5, despite the British team being considered the favorite. The final was hard-fought, with the Italians dominating from the start, leaving the British behind and finishing with an 8-second lead, a narrow but decisive margin.
During an interview, Giulia Conti commented on the achievement: “We have written the history of women’s sailing by proving we can race on these boats. A truly great experience that represents a new step toward our access to the men’s America’s Cup, and the hope that in the future there may be a woman aboard an AC75. We would like that access to be based on merit and not through a quota, but that will depend on who wins the America’s Cup and what rules are set. Above all, it was brilliant to place our final between the first two men’s races.”
The women’s event took place during the America’s Cup grand final, an extraordinary stage in which the Italians shone among the world’s best. Yanmar, official sponsor of the America’s Cup, supported this historic competition, which saw Luna Rossa’s women’s team emerge as champion.
This historic triumph comes after the victory already achieved by Luna Rossa’s youth crew in the Youth America’s Cup, further strengthening the Italian team’s reputation on the international sailing scene.
Max Sirena, Skipper and Team Director of Luna Rossa Prada Pirelli, emphasized the importance of the victory, praising the sailors for the hard work and determination that led them to the finish line. “This victory is a source of pride for the entire team. It proves that our vision towards the new generations of sailors was right and that our training program has paid off”, said Sirena, highlighting how both victories, youth and women’s, have opened a new era in the history of the America’s Cup.
Simone Salvà, coach of the Luna Rossa women’s and youth teams, also spoke enthusiastically about the achievement, praising the skill and perseverance of the girls despite their limited experience in match racing. Salvà described the journey that led to the creation of a solid and talented team, capable of competing and winning at an international level.
With the historic double win in Barcelona, Luna Rossa has proven that the team’s future is bright and that training the new generations, both male and female, is the key to success.
Carasco, 19 March 2020 – Cartello Srl is close to its customers and all the citizens facing the coronavirus emergency.
As known, the moment we are facing is really thorny, as never before. We find ourselves in a real situation of emergency, so that we are called to acts of responsibility and perseverance that will allow us to overcome the difficulties we are facing in the best way. For this reason, Cartello wants to express its closeness to its customers and to all the citizens of the hit areas: we are part of the community and stay by it in such a complicated and challenging moment.
The main aim in this moment it to protect our health and physical integrity. Consequently, we adopted in our company measures to safeguard the safety of all the personnel: we are still working, but complying with the indications given by the Italian government, we are employing where possible Smart Working modalities and shifts, as well as putting into practice all the measures needed to keep the workplace constantly sanitised.
Cartello, therefore, is still operating thanks to the work and sense of responsibility of all the employees and the network spread in the whole Italian territory, even if with the limitations imposed by the current government prescriptions. We are trying to keep close to all those following us with affection and to contribute to our country and each of us efforts actively taking part in the #istayhome campaign. It is possible, indeed, to find on our Facebook and Instagram social channels some sparks about activities you can do staying home for all the sea enthusiasts and for all those interested.
We thank our employees, collaborators, dealers and all the citizens for these days efforts, hoping to come back soon to our normal activities.
During the Cartello Training Courses 2019, our dealer have tried themselves at a series of tests to verify what they had learnt on different levels. All the participants had to challenge each other and test their knowledge on very difficult theoretical subjects and practical tests regarding electrotechnology and the use of the oscilloscope.
All the dealers have shown to have a really high level of knowledge and such experience to assure a more than adequate assistance to Cartello‘s clients. Only one, however, has been able to triumph over the others, by proving to have uncommon competences and gaining the sought-after prize Cartello offered: it is the case of Daniele Stellati, from Cosmonautica Srl, in Montescudaio, Via Poggio Gagliardo 41, in the province of Pisa.
Daniele Stellati takes home a wonderful prize, worthy his abilities: Cartello has decided, as a matter of fact, to offer the winner and one partner he chooses, flight, accommodation and a ticket to take part in the Boot Dusseldorf, taking place from the 18th to the 26th of January 2020. The lucky two, moreover, will have the opportunity of taking part in a dinner with the Yanmarteam and follow the new Yanmar engines series launch conference!
Congratulations to Daniele Stellati and all the participants and…enjoy your trip!
Last Thursday, Cartello took part in a wonderful award ceremony that took place during the ha partecipato ad una meravigliosa cerimonia di premiazione svoltasi nel corso del Salone dell’Orientamento in Genoa, at the Palazzo della Borsa. In this occasion, our company, together with many others, has been awarded because of its availability to participate in the orientation and training project launched by the Liguria Region#Progettiamocilfuturo.
The Regional Councillor Ilaria Cavo has been the patroness of the event: she has personally delivered the award to all the participants, emphasizing how important the participation of companies and professional to support young people from Liguria is. “I believe it is a really significant project”, Cartello’s Communication Manager, Rosa Finizola, commented, “that helps to fill the gap between school and the world of work. I have considered important for Cartello to join the project since young people very often do no t know how company internally work and what the different figures do: to come here to our company, to be trained and oriented by us, will help them to see with their own eyes and understand the daily work activities, in order to make more conscious choices. ”.
The journey that will be made by students is articulated in four main phases: self-knowledge, knowledge of the marketplace, knowledge of the society and knowledge of the formative opportunities. Cartello is part of the context of the second phase, offering students the opportunity of understanding how a small company, capable of acting on the whole Italian territory and also some other European countries works, in such a central field for Liguria as navigation is.
The aim is to help the students to figure out how they imagine their working future, how concretely the world of work functions, to rely more on their skills and feel more motivated. We at Cartello are proud to be part of the group of testimonials and hope to give a positive contribution to all the young people from Liguria, in order to help them find their way.
Cox Powertrain, the British developer and manufacturer of high-powered diesel outboards, is reporting the successful completion of the first round of in-field outboard validation tests by the US Navy. Following the trial of two CXO300s aboard a 9m RIB last week, when the engines achieved a cruise speed of 43 knots at 3,600 rpm, Naval Sea Systems Command (NAVSEA) testers expressed great enthusiasm and excitement about their performance.
The US Navy has been exploring the use of technologically advanced engines in an effort to improve combat readiness, crew safety and equipment supportability. NAVSEA is responsible for delivering the best possible equipment and systems to the US Navy and the recent trials were run by Brandon Bagwell PE, Senior Mechanical Technical Manager and Project Lead for NAVSEA’s Combatant Craft Division.
Cox Powertrain’s Global Sales Director, Joel Reid, commented: “This first round of the in-field validation programme has gone extremely well and exceeded all expectations. NAVSEA’s testers seemed impressed by the smoothness of the engines and the absence of noise and smoke, which is historically associated with diesel engines. We were delighted that the two CXO300s went beyond their target to achieve a cruise speed of 43 knots”
The CXO300 has generated worldwide interest from civil and government agencies operating fleets of fast response vessels. This game-changing diesel outboard offers the ability to meet the demands of NATO’s single-fuel policy, as a safer alternative to gasoline, while also providing exceptional performance and greater range than equivalent 300hp gasoline outboards.
Cox’s engineering team, led by Stephen Moore (previously Director, Base Engine Engineering at Ricardo), has spent over a decade developing and perfecting the highest power density outboard ever created for a marine application. With a four-stroke V8 architecture and a package of similar size and weight to a gasoline outboard equivalent, the CXO300 delivers the performance and efficiency of an inboard with the convenience and flexibility of an outboard. The CXO300 offers at least a 25% better range and 100% higher torque than leading 300hp gasoline outboards, enabling the craft to move higher displacement vessels more efficiently and get vessels onto the plane quicker.
Production of the CXO300 is set to commence at Cox’s state-of-the-art manufacturing facility later this year, following over £80m of investment in the firm over the last ten years. Cox is supported by a worldwide network of 40 distributors and around 400 dealers.
First CXO300s expected to come off Cox Powertrain’s state-of-the-art Shoreham production line in Q4 2019.
Innovative diesel outboard manufacturer Cox Powertrain has announced at Seawork that production of its much-anticipated CXO300 will commence in October, with the first round of delivery to take place by the end of the year. The firm has received a “remarkable” number of enquiries since its order books opened in November last year. When fully operational, the production line will run two shifts per day to meet this exceptional level of demand.
Cox Powertrain’s smart technology driven assembly line is the result of a collaboration between the Cox Manufacturing Engineering team and QM Systems, one of the industry’s foremost providers of automation engineering services and solutions. Cox has invested an impressive £6.7m in creating its new production facilities, which includes an integrated state-of-the-art Manufacturing Execution System (MES) that will ensure exceptionally high-quality standards are consistently met with a ‘No Fault Forward’ philosophy.
This level of investment is in line with the firm’s ethos of making use of the very best research and development procedures, taking its lead from the type of systems used by premium brands in the automotive industry. Many of the firm’s key staff have backgrounds in the automotive industry, hailing from prestigious firms including Jaguar Land Rover, Cosworth and Lotus.
Smart technology will be used throughout the process. The assembly line will include numerous features to guarantee the flawless quality of each Cox Powertrain outboard such as a camera system to verify the continuity and exact size of each bead of sealant laid down by the bespoke plotter to ensure the perfect seal; WIFI enabled DC tooling that will communicate directly with the MES system to record all assembly torque data; an automated ‘Spin rig’ to test every gearbox and a comprehensive end of line ‘Hot test’ facility to ensure each powerhead achieves the exacting standards that our customers require and deserve.
Cox Powertrain’s Operations Director Jerry Attridge said: “This is a very exciting time for everyone at Cox Powertrain. Not only is the CXO300 a superb, innovative product, we are also creating a complex, high precision manufacturing facility using cutting edge technology to deliver what can only be described as a game changing product into the marine outboard market. Thankfully, we have built a fantastic team of people that I am certain will deliver a transformational product.” Cox’s 4.4-litre 4-stroke V8 CXO300 has been shown to offer excellent performance with maximum torque delivered right through from 1,300 to 3,000rpm, reaching 479ft lbs ̶ almost double the twisting power of its 300hp petrol rivals. Predicted cost-of-life savings are as high as £150,000 due to reduced fuel costs, fewer maintenance requirements and an expected three-times-longer life span.
Cox Powertrain has been announced as the winner
of the Marine Power and Propulsion category at the annual Seawork International
Innovation Awards for its game-changing engine, the CXO300.
Cox Powertrain, the British diesel innovator behind the world’s first 300hp diesel outboard, has been announced as the winner of the Marine Power and Propulsion category at the annual Seawork International Innovation Awardsfor its game-changing engine, the CXO300.
The awards, sponsored by A-Plan Insurance, celebrate the outstanding individuals and innovative companies that comprise this vibrant and productive industry sector. All products involved in the awards comprised new vessels or projects that were launched or completed within the last 12 months and which demonstrate fresh approaches, rather than being enhancements of existing products.
Judges chose Cox Powertrain’s pioneering CXO300 for its novel design and the boldness of its from-scratch approach. They recognised that instead of modifying pre-existing components, Cox’s designers opted to pursue innovation in every aspect. The fact that the CXO300’s service life is anticipated to last three times longer than conventional petrol outboards was another major point in its favour.
“We are very proud to be handed this award,” Faye Dooley, Marketing Communications Manager at Cox Powertrain commented at the waterfront Golden Arrow Marine restaurant, where the awards were presented. “Not only have we worked hard to create an innovative product, we have also redefined standards in service, and we are extremely proud to be recognised for this.”
