Behind the Quest to Build the World’s First Diesel Outboard Engine

Charles, to start, when and why did the notion of a marine diesel outboard engine strike you as a good idea?

We have to go back to 1966 when I was 20 years old, believe it or not, in Greece, where we were staying on my mother's ancient wooden Greek boat, Kaiki. I was decanting petrol from a large container to a small one for our outboard motor and spilled a large quantity on the deck. A second later it erupted into flames and a very serious fire ensued. Luckily no one was hurt and we did contain the fire, but it left an indelible mark on my life after that. So that was really the initial instigation in the back of my mind that somebody one day needs to come up with an outboard that uses diesel.

What do you consider to be the pivotal moment or relationship that made Cox Marine ago?

For 50 years I felt the solution needed to be found for this, and the key was looking at marinized inboard engines. They were lorry engines that were converted for marine use; wonderful engines, extremely long lives, but they're very big and heavy. (Big and heavy) was never going to be an option for an outboard motor, and the key was to get the size and weight of the engine down. And then just over 10 years ago I was introduced to David Cox.

David had a career as an outstanding creative engineer with a background in Formula One racing here in the U.K. He had been looking at designing a lightweight diesel for a different purpose, military drones. I spotted in that an opportunity to look at the possibility of using this creative thinking, mainly driven from Formula One racing where there's a culture of driving engine power up and weight down. So that was when the dream started to become a reality.

When you look back at the company that you created in 2007 and the company that you see today, how is it most the same and how is it most different?

Cox is most of the same because of our ability to analyze technical challenges, work through them, resolve them and deliver. So, at the outset, we were entirely focused around how do we create a brand new diesel outboard competitive with gasoline outboards; a considerable challenge. Along the way we've produced a great list of patents which is a strength to our business.

Where we're most different today is that we've transitioned in the last 18 months from being an early stage startup, effectively a startup development business, to a full-blown manufacturer supplying product to a global market. This has involved a big shift in culture, skillsets in our organization, as well as the development of a number of commercial relationships around the globe on the supply side, and even more extensively on the sales side, through our distributors, which we've amassed across five continents. So, the transition from a developer of technology to a manufacturer and seller of that technology globally, that's the migration we've been through.

I'm sure there have been many hurdles along the way. Which was the greatest and how did you get over that challenge?

Undoubtedly the greatest single challenge was the power head, getting the weight down and to the package size that is comparable with a petrol outboard, because conceptually we wanted the diesel outboard to be interchangeable (with the gasoline version). Getting the weight out and the package size down meant looking at every single component from a blank sheet of paper and seeing how we could maintain its strength, but do it with a minimum weight. And this really came from our Formula One background and heritage from David.

What is it about your new engine, the CXO 300 in today's decarbonization environment that tells you this is the engine of the future?

I think that's a really good question, and there is no doubt that market has already changed to some extent. It certainly has in automotive big time, and aviation and marine are definitely looking at how best to decarbonize. What I will say is that I did a degree in physics and I was given an option of a topic that I wanted to write about in my degree course, and I chose the application of hydrogen and fuel cells for automotive in inner cities, because I'd been brought up in London through two huge smogs which had killed tens of thousands of people through pollution, and I was very aware then, as a young man or child in the first one, how dangerous nasty pollution can be. I, and everyone at Cox, are very conscious of that.

I think it's all too easy, reading the headlines, to forget why diesel has become such a dominant fuel source for marine for so long. And that is that we save 25-30% in terms of fuel, and that means that the carbon dioxide emissions are similarly reduced by 25 to 30% versus gasoline.

It's also true to say that the new emerging technologies are not there yet for marine. In marine, you need to be able to go offshore; you need range. Battery technology is, at the moment, not there. Hydrogen could be an answer, but truly green hydrogen is not yet available. So, to answer your question, we believe that this is a good solution for the moment to reduce emissions and that we have a pathway of at least two decades and probably three. But we're not going to sit on our hands. We are going to carry on innovating and looking at what technologies could be used to further improve our carbon footprint.

Let's fast track to today, if that's okay. Can you give us a by the numbers look at Cox Marine using the metrics of your choice?

Yes, I've just got a few for you: 10 years from first concept to reality; 150 members on staff; nearly $200 million invested; and hundreds of engines operational in 21 countries across five continents. Plus 4,000 units per annum is the capacity of the existing production facility we built in the UK.

You've already discussed many of the hurdles that you've had to overcome, but it's taken a long time for the CXO300 to get into production, with the first unit just coming out in 2020. Simply put, what took so long?

Looking back at it now, I don't think it actually has taken us very long. If you look at the cycle time for brand new products in other industries, they're typically 5 to 10 years if it is a genuinely new product. Now throw in the fact that we had to develop a totally new diesel engine layout which has never been done before, one with a vertical crankshaft, and then on top of that throw in a global pandemic, I don't think effectively 10 years from original inception and less than five since the base design was settled on is a very long time.

What are your monthly engine production rates, and looking at the coming five years, how do you see that evolving?

We're still at the backend of a pandemic, which has brought with it, supply side, logistical problems, shortages of containers, and bottlenecks all over the place. We have deliberately reined back production in the short term, partly because of those factors. But also because we want to walk before we run. At the moment we're producing 10 units a week. (*Note: this interview was conducted in August 2021). Our short-term plan is that this will gradually rise through the rest of this year to 40 a week, and then of course, as the market evolves, our plan is to get to our target rate of production from the existing facility of 80 to 90 units a week.

For readers that are considering an outboard diesel engine, what do you consider the main advantages for the diesel version?

It depends on what the use case is. But the majority of our early adopters will be in the, what we would call the commercial segment, whether it's coast guard or other commercial operators, or indeed the high-end leisure market, typically super yachts, where these boats and engines get used a great deal. And there, the principle driver to adopt one of our engines is simply the fuel saving. We've got one customer who is a heavy user who's already estimated, their numbers, not ours, an annual saving of $150,000 for each pair of Cox engine they're using versus gasoline. That's a huge payback. There's an immediate financial benefit for anyone who's using the engine a great deal. It is true the engines are more expensive initially, but you get paid back very quickly, over months, not years.

On top of that, for the wider market, you can add substantial increase in range from the same size fuel tank. Fuel safety, obviously, which I've touched on. And I think also importantly, particularly outside the US, is the ubiquitous availability of diesel on any part of the coastline where obviously there's human activity, which cannot be said of gasoline. In other parts of the world, gasoline is actually quite difficult to get hold of versus diesel, which is used by everyone else on water. Large boats use diesel almost exclusively. Availability is, I think, another big driver for many, many people.

I know that we can easily explore the technical specifications of the CXO 300 online, but can you take a moment and discuss what you see as the key technical attributes and parameters of the engine?

This is a big and powerful engine, and I think the key number is 300 horsepower delivered at 4,000 RPM. It's a conservatively rated engine. And we offer 479 ft. pounds of torque, which is a lot of torque for an engine of this size and delivered over a very broad rev range. The engines give a lot of grunt at low revs. Obviously the 25 to 30% fuel savings versus gasoline. We offer two gear ratios, so prop end speeds of 2,750 and 3,200 RPM, which is useful for different use cases. We also offer a wide range of leg lengths. 25 inches, 30 inches, and 35. Not all the 300 horsepower petrol guys are offering three leg lengths, but we decided we wanted to cover pretty much every conceivable application that our engine might be used for. And finally, long life. We anticipate our engines having three times the useful life of a petrol outboard.

What’s next for Cox?

It is early days for us. We've just launched our first product, but we are already are looking at new product cycles yet to be announced. What we're doing is looking at the clear trends that exist in the premium petrol outboard market, especially with the move towards higher power. So, when we first set out designing this engine, we went for 300 horsepower because, at the time, that was the largest petrol outboard. It's interesting that in the five years since we settled the design, the petrol outboard market has actually moved, as you know, quite a long way, 450 being reasonably commonplace last year, and now even 600 horsepower. There's no doubt that we will be looking at some point in the future, not too far away at higher power outputs. The core technology is available to do this.