When Rudolf Diesel unveiled his engine to the world in 1892, it was nothing short of a revelation. Today we reserve our excitement for batteries and electric power, the miracle of the combustion cycle having been almost forgotten. Once a degree of reliability is reached, our attention wanes… until it goes wrong.

Sitting at the heart of even the most advanced hybrid yachts is a diesel engine, albeit one driving a generator to produce electricity. Despite the rapid growth of electric technology and ‘clean’ energy across yachting, the marine diesel engine will have a role to play for many years to come as a source of battery charging.

Despite this, its basic workings remain a mystery to many. But as I found out after spending four days in a workshop looking just at marine diesel engines, a little knowledge goes a long way.

The UK Sailing Academy runs the Maritime and Coastguard Agency Approved Engine Course (AEC) regularly. Its purpose-built workshop has several marine diesel engines, generators and outboards. The four-day AEC course costs £740. Photo: Will Bruton

Common problems

Lyndsay Rufford has been a marine engineer for over 30 years. Watching him work on the Oyster 575 I am getting ready to sail down to the Canary Islands is an education. Far from the grimy operation of local car garage, Lyndsay could be described as borderline clinical in how he works.

Every tool he will need is set out ready in order; the engine room is brightly lit by a series of carefully positioned floodlights and the interior surrounding it covered in protective materials. Nothing left to chance.

A veteran of Oyster’s World Rally pit stops, he has found himself parachuted into some of the world’s most far-flung cruising grounds to problem solve. But what can owners do to help themselves?

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“My job has become more and more technical over the years, as layers of complication like turbos and electronic engine management systems have been added to achieve efficiency legislation targets,” explains Rufford.

“Diagnosis of most problems hasn’t changed that much though, and owners can tell quite a lot about what might be going wrong with a little knowledge of the first principles of how the marine diesel engine works. With a diagnosis, you can make decisions.” Peering over his shoulder, I am reminded of how little I really know.

Simon Brown is just one of an increasing number of yachtsmen running a boat with two marine diesel engines and many complex systems on board. His Oyster 56 Britican has thrown him some curveballs over five years of ownership, but he now feels he has got to grips with even the more complex maintenance. He documents the challenges on his vlog Sailing Britican.

UKSA engine instructor Ray Charles explains the workings of an outboard motor. Photo: Will Bruton

Before leaving on his circumnavigation, Brown undertook a diesel engine course, but it is along the way that he says he’s learned the most. “There has been some very steep learning. In a consistent Force 8, the generator out of action, the alternator too, with no way to charge, in a big sea, with my wife and young daughter on board…

“The most frustrating thing we have dealt with, though, was one of the engine hoses giving up quite early on, covering the engine in water. This caused it to short out and, much more alarmingly, take up the habit of starting on its own randomly.

“That was a lesson in pre-emptive maintenance. If a part, particularly a hose, looks worn, replace it. Looking back, we have got so much better at that.” Brown now confidently takes on 200-hour servicing of the engine and generator, but when it gets more complicated he will bring in an engineer and closely follow what they are doing to expand his knowledge of marine diesel engines at the same time.

Listing every component as it is removed helps ensure nothing gets lost. Photo: Will Bruton

“Now we use professional engineers to learn more ourselves, taking care to choose carefully who we bring on board. Recently we had the injectors serviced on the main engine, I watched, then serviced the ones on the generator myself. You are paying for all that knowledge, so make the most of it and get to know your engine better at the same time. The hourly rate is the same.”

Fuel problems are high on the list of concerns for those bunkering far from marinas and reliable supplies. “You learn quickly that what goes in has to be good otherwise it can cause a world of problems,” explains Brown. “If it looks even vaguely dodgy, I now take a sample of about a litre and leave it to stand for around 15 minutes. One we recently took had roughly 10% water in it!”

Paul Bennet, owner of the Compass Maritime Group, has seen numerous examples of marine diesel engine training getting crews out of trouble over the course of his career and says it’s mostly about diagnosis.

Rocker cover removed and valve gear exposed. Photo: Will Bruton

“One memorable incident was a yacht off Cannes with engine trouble. As soon as the engineer on board identified an eggy-smelling fuel, it flagged that they might have a diesel bug. Further investigation confirmed this and the engineer was able to bypass the fuel filtration system with treated spare fuel and get the yacht into port. Nothing that complicated but without that knowledge the yacht was going nowhere.

“Other issues can be more pre-emptively tackled. For example, if you know your engine reasonably well, you know roughly how hot the parts run at. An overheating gearbox is something you can pick up on by doing regular checks, and fix by simply cleaning the gearbox oil cooler. Again, this is all about getting involved in the engine room early on and having that baseline of knowledge to help you diagnose what is going wrong.”

Getting to grips

For many aspiring professional yacht engineers, the MCA Approved Engine Course (AEC) will be the first time they strip an engine down to its component parts. The United Kingdom Sailing Academy (UKSA) runs the four-day course, and is increasingly seeing leisure sailors signing up to learn more about their yacht’s workings.

Those joining my course include Stephen Rishworth, about to sail his Discovery 55 around the world with his partner, as well as an aspiring superyacht engineer, a wind farm boat skipper and resort watersports manager. All were on the course to imbibe as much information as possible.

Our instructor, Ray Charles, ran patrol boats for the MoD Police and has over 30 years’ experience in engines. The course schedule is packed, information coming thick and fast. On the first day we were presented with two fully assembled marine diesel engines, by the next we have split into two groups to strip them down to their components, swapped engines and put them back together with the aid of the other team’s notes.

Using feeler gauges to determine gap widths down to a tenth of a millimetre. Photo: Will Bruton

Again, everything is rather more organised than you might expect, with every component carefully labelled so a job can be handed over half way through. While not so relevant to the average yachtsman working alone, if tired, it’s a practice that obviously helps prevent mistakes.

As someone with a fair amount of experience finding my way through problems on board, the course gave me a window into the world of the professional engineer. Ray is of the old guard. We are (gently) chastised for things dropped ‘into the bilge’, knowing that if we were on a boat, not in a workshop, they would likely be a nightmare to get back.

Some dark arts of the engineer are also demonstrated, like how to make an emergency gasket out of a paper chart. “The paper is the perfect thicknesses,” explains Ray. The result is surprisingly impressive.

Diesels Afloat by Pat Manley is a comprehensive guide to maintaining, troubleshooting and repairing marine diesel engines (published by Fernhurst Books)

And while precision measurements are taken with micrometers and feeler gauges, there’s a down-to-earth understanding that many of us are learning these skills to get us home rather than onto the career ladder of the professional marine engineer.

By the end of the course we have also covered gearboxes, fuel systems, and outboard motors. There’s no shortcut to mastery of the marine diesel engine, but an understanding of first principles that, with manuals at hand, is seriously empowering.

Modern yachts have numerous ways of getting help remotely, but the fundamental understanding of how the engine actually works makes it possible to diagnose problems more quickly and, if necessary, make the ‘get you home’ fix that might just save the day.

First published in the December 2019 edition of Yachting World.