Boat perfection, diesel engines, who does is best? and, how to keep them going for years.

Twin MAN diesel engines

The marine diesel engine, available in power outputs from less than ten ponies right up to the largest I have seen being in the 2500hp range, in line, V configuration, four stroke, two stroke, mechanical, electronically controlled, even some very small ones with a hand crank. If looked after, there is no reason why they should not go for literally thousands of hours of use, some tolerate more abuse than others, but, who makes the best ones that will not see you tearing your hair out in frustration and opening your wallet at every given opportunity? and, how can we ensure that they last as long as possible?

I have written about various things, including perfect boats (on another platform), my list of GOAT (greatest of all time) boats is an example of some boats I consider worthy of wearing the crown, but there is none on my list or that I know of in existence that are the best at everything. Seeing as we are at that time of year of lists of all kinds, best of year, best of the decade so far and best of all time, I thought I'd throw my sou'wester in the ring and make my own list.

Small mechanical diesel

The old fashioned mechanical diesel marine motor, may they live forever, there is something comforting about not having any electronics to worry about or requiring massive electric power in order to maintain networks and a host of sensors. Simple and robust with the ability to be maintained without diagnostic computers, so a lot more mechanics and boatowners themselves can attend to them. Small is a relative term, let's say lower horsepower, two, three or four cylinders, the typical motors you see is smaller sailboats or generators, a real workhorse, naturally aspirated (no turbo), nothing complicated.

My pick for the best is Yanmar, a Japanese company that has been in business for over 100 years, the smaller motors are usually based on other Japanese engines from Kubota & Toyota. Admittedly, mechanical diesel engines are robust by nature, but these things just never seem to die, they are the least likely brand overall to be in the yard for large repairs, with basic maintenance these motors will probably outlive you and the rest of the boat.

Honorable mentions, Beta Marine & Solé Advance, Beta is a British company, they get bonus points for painting their motors in fire engine red, I like that, a marine surveyor that I know chose Beta to repower his own yacht, that should tell you something. Many moons ago we had a small fishing boat that we repowered with a Beta motor, it was perfect. I seem to remember but don´t quote me, it was a Perkins based motor.

Solé is a Spanish company, like Yanmar they have been in business for more than 100 years, I see them a lot in Spanish built llaut style boats as well as and possibly more telling, commercial fishing boats, a lot of the motors use another Japanese base motor, Mitsubishi, there is obviously a pattern here.

Mid size mechanical diesel

We now move up the power spectrum, not sure if I could put an exact power figure on this category, but let's say small to medium sized powerboats, often with twin motor installations and with planing hulls, new (not rebuilt) pure mechanical diesels in this size are really uncommon now, they have gone to electronic control of at least some form. We are talking about units you would find in second hand boats.

This was a really hard choice, there are many that are so good and give a very long service life, so I have decided to make it a three way tie, Yanmar, Caterpillar and Cummins.

Yanmar, making a second appearance on the list, the 4LH 4 cylinder engine, one of which I know personally to have 5000 hours of use with its original starter motor and alternator, the owner doesn't even take brilliant care of it, the other motor is the 6LP range, these can be in V drive, conventional straight shaft or Mercruiser outdrives, rated at 315hp more or less, based on the Toyota Land Cruiser motor, it is just as indestructible as the vehicle from which it came. They are not the quietest, over time they will smoke at startup, this is fixed by sending the injectors out for service and, err, I'm struggling to think what else, change the cambelt at about every 1000 hours and that's more or less it, look around the motors and you can see some of the original Toyota stamps on certain parts.

Caterpillar, a staple of the recreational and commercial marine market for decades, the two motors that spring to mind are the V8 3208 series, available right up to 435 horsepower and may use electronic throttles and gear selectors even though the motor is mechanical. I cannot begin to list the number of boats I have seen with these motors, the oldest boats I know with these motors are from the 1970s, mechanically simple, robust and with parts still readily available, it is not a motor I would be worried about having, I am old fashioned and prefer them painted in yellow over white. If there is one drawback, due to their V cylinder configuration, they are quite wide, so if you have a narrower beam on your boat, make sure you can reach things on the motor or be prepared for some boat yoga.

The in line six cylinder 3116 motor is another common installation, Sea Ray used a lot of these motors, they are in an in-line configuration so are considerably narrower than the 3208. The 6.6 litre motor pushes out up to about 350 horsepower, not really stressed, I believe over the years this motor evolved into the much more modern C7 series of motors (please post a comment if that is not correct).

Cummins, the B series motors, four and six cylinder, from another company with 100 years of know how, this motor has gradually developed, common rail fuel injection, and the last of the motors have some electronics, but in my experience they are trouble free. Cummins did a tie up with Mercruiser for a long time, allowing you to see engine data using the Mercury Mercruiser Smartcraft system, these motors are also available to be coupled to Mercruiser Zeus pod drives, Pod drives, twenty years later, are they as good as was promised?

Honorable mention, Volvo, I have not always been their greatest fan, but, their older mechanical motors, the TAMD series and also the KAD motors are fine, I would have no problem with them in my own boat, what knocks them off being in the top three is some parts are outrageously expensive and a few bits and pieces becoming more difficult to source, Volvo were fairly early with their electronic controls and engine management, the EDC and EVC systems, the former for engine control systems such as fuel injection and the latter for gears and controls, I personally would try tp avoid the early EVC systems, they might have been okay when they first came out but some systems are now 20 plus years old, the EDC systems themselves seem to be okay by and large, but expensive to replace or fix if needed.

I would be happy to have any of these motors in my own boat, yes some of the motors will be getting on in years, but with regular maintenance there is no reason that they will not carry on for many years more. Be in no doubt, the older motors will be considerably different to their modern counterparts, if you buy a boat with mechanical diesels there are definitely two areas of improvement I would investigate and remedy;

• Noise, engine room insulation can be changed, there are better, newer materials that will make life on board much more comfortable. Sound insulation is a strange thing to upgrade, even the fewest less decibels heard from the diesel motors makes a huge difference. Insulating or renewing the insulation around the engine room hatches also makes a difference, the original foam is often squashed completely flat or missing pieces, replacing this is easy as upgrades or repairs go and makes a noticeable difference.

• Engine breathers, a lot of older motors will vent gases from the engine block straight into the engine room or have some crude method of aiming the breather towards the engine intake system, Yanmar do this will their metallic air filter covered in foam. I would upgrade these open systems to a closed system, such as a Racor CCV, it will stop the engine room being so greasy, you can direct the filtered gases back to the engine oil pan or into a catch tank, which is what I would do. At the same time I would upgrade the air filter system if there was enough room to fit a different one, Racor can supply these also. It is nothing new, the newer motors are all equipped with these systems, Detroit Diesel who had a reputation for oil leaks at one time used Walker Air Seps, this helped quash the oily engine problem.

Mid size electronic motors

Now we are looking at larger boats with probably more distance between the engine room and the helm(s). This category is also difficult to put an exact figure on, what is now considered sort of mid sized, lets say for our purposes is up to 1000 horsepower.

Caterpillar and MAN take the gold medal here, there is no doubt for me. Caterpillar with their in line motors make for more space in the engine room, MAN too offer in line motors, Riva and Azimut have some models with these motors and the engine rooms are very easy to get around for servicing. 

Honorable mention, Volvo, in fact the Princess V50 I rate so highly, is powered by a pair of D12 715hp motors. I find that Volvo seem to be much less prone to throwing error codes when they are installed in a shaft drive configuration, the D12 and the newer D13 are very smooth motors.

Big motors

Now we move up to the real heavy hitters, what is strange is that not so many years ago, the motors from the mid size bracket were considered large and powerful, the goalposts have moved considerably. We are now talking about motors that are physically large as well as being hugely powerful, this does not always mean that the motors will be installed in really large boats, over say, the last two decades increasingly more powerful motors have been installed in smaller (relatively) boats, sportfisher type boats are a good example, its not uncommon to find models in the sub 80 feet category (a big boat but not outside the realms of recreational boating or in this case fishing), where the base engines are in the 1900 to 2000 horsepower range, I say base, because optional motors can go to 2500+ horsepower. Now consider this as a comparison, I think it was last summer we had a 112 Ferretti Custom Line in the yard, a beautiful boat but even though she was a personal craft and was not used for commercial purposes, she is considered too large for normal recreational boating, the V12 motors that powered her to surprising speeds were rated at about 2000hp each, this boat was about 20 years or so old and a whole 40 to 50 feet longer than some new boats packing even more powerful motors.

For these huge motors it is a three way tie MAN, Caterpillar and MTU (part of the Rolls Royce group of companies), any of these motors in the huge power outputs will serve you well,  V12 and V16 engines with engine capacities of 30 to 50 litres, sometimes more are very common, engine room auxiliary panels with engine data readout and remote start and stop are normal, I have also seen a lot of these larger motors and some of the smaller models installed with emergency control panels at the helms so in the unlikely event of the main engine controls failing you have a backup.

The physical size of these motors and their enormous power outputs is actually not the most astonishing part, the marvel is how can this beast of an engine can run so smoothly, some of the figures are sort of amusing too, apart from the huge engine capacities, take that Ferretti I mentioned, that had twin V12 MTU motors, the main agent was performing the engine service, each engine needed 250 litres of oil and about 160 litres of coolant, the air filters are the size of dustbins and the turbochargers could be mistaken for flying saucers.

Fly by wire and not pull by cable

Electronic controls for marine diesel engines have come a very long way, some of the earlier ones had a long delay going from neutral to gear, I remember a couple of boats in particular where the initial surge was at least a second before anything happened, it was quite unsettling until you got used to it, a 53 foot boat with twin Caterpillar diesels, the sudden inertia took getting used to, now the latest controls have no delay, are reliable and very smooth with all sorts of features, some of the most useful are;

• Engine synchronization, automatically syncs both motors so they run at the same revolutions.

• RPM control, I like this one, you can up and down the engine rpm by the touch of a button, something of the order of 50 rpm at a time, far more accurate than doing it manually.

Some credit has to go to Caterpillar, their controls are really nice to use and have easy to read buttons and the rpm controls integrated into them. MAN use (or used) Bosch Rexroth controls, lovely positive action, ZF gearboxes also have their own branded controls, I suspect they are Microcommander or Mathers units, I have used them a few times with newer MAN diesels and have no complaints at all.

Glendinning is another company worthy of mention, I have used these a lot with Cummins diesels, also have seen them retrofitted to Volvo motors. I am usually the first to moan about more electronics but actually in this instance the number of times these brands have given me any bother, I could count on one hand.

Nice touches

It's nice to be able to talk about some useful and well thought ideas rather than complaining, it seems to vary from boatbuilder to boatbuilder or maybe just each installation for a given boat is different, but there are two things I really find useful;

• Handed engines, not the rotation of the engines themselves but where certain service items have been "handed" on the engines so that they face the inboard sides of the motors. Usually, for service or daily checks, filters, oil level dipsticks or coolant reservoirs are located wherever the engine builder installed them, you had better hope there is enough room to reach them or that the engine hatch opens enough. On diesel installations, the easiest place to access is in between the motors, so handing the motors means where possible as much as possible of the service items have been faced towards the space in between the motors, it makes life easier.

• Oil fill direct to the sump (oil pan), I have seen this a couple of times, in both instances it was in engine rooms with ceilings that were so low, the conventional method of topping up oil via the rocker cover on top of the motor was impossible, so the oil pan had a spout a bit like a teapot, right next to the dipstick where you topped up engine oil, brilliant idea, in both instances this installation was on Caterpillar diesel motors.

You must follow the rules

A bit of a peculiar thing to say? High performance diesel motors do not like to plod along for hours at displacement speeds, so if you intend to go a long time just chugging along, a different motor and possibly a different boat will suit you better, I wish to tell you a story, one of closest friends used to be a captain on a 60 foot yacht with twin 1100 V10 MAN diesels, beautiful motors, well, for some unknown reason, the company who managed this yacht on behalf of the owner told him he had to make the 500 nautical mile journey at no more than ten knots! Now, ten knots in this boat with its planing hull is barely much above idle, he told them it was a mistake, the engines would not like it and at the very least every so often he should open the taps and let the motors spool up, but no, they were adamant, fast forward to the end of said journey and almost three days later, sure enough, alarms a plenty!

I can't remember the exact number or which ones, but I seem to recall exhaust alarms and possible turbos nonsense too, when MAN came to investigate, they connected their computer, saw the previous engine run history from its normal trouble free operation to itś new and sorry state, then proceeded to sort out the issues, following the MAN handbook. In the end there was a five figure invoice and the management company was fired, the cost of the invoice was more than the cost of the fuel had the boat been run normally.

Imagine if you will buying a high performance car, let's say something angry and Italian then insisting on driving round and round the city centre, eventually the motor says "what are you doing?" and starts throwing codes. I used the example of MAN because it is a first hand account, but they are not the only ones, big motors with big power need to be let loose, displacement speeds due to bad weather are one thing, but, as soon as you can, give it the beans, or, as my marine engineer brother would say, "run it like you stole it!"

I would also like to add another point to rule following and maybe even a bit of myths and legends, or, perhaps just my personal preference. I tend to avoid thrashing diesel engines until they have got to temp, this can sometimes take a while, what I look for is a steady engine temp climb and then the sudden reduction in temp when the thermostat opens or, simply the engine temp does not keep rising.

Diesels warm up better under load, after checking water circulation and gauges, try and set off sooner rather than later, by the time you have dropped your mooring lines the oil should be circulating around the motor. The exception I suppose for not thrashing diesel engines are generators, they mostly are set up to run at a steady, fixed speed, so virtually straight from startup they get up to their rated running speed.

What ruins diesel engines

Going on experience and also the work performed on pre owned boats before going out to new owners, I would say that two things will cause a diesel engine to not work well, fuel and cooling, especially cooling. Modern diesel motors have sensors that detect water in the fuel, you can have these fitted to certain types of diesel pre filter too, contaminated fuel is a problem, especially to modern high output diesel motors. The latest MAN six cylinder engines for example, they range from 730 to 850 horsepower, the injection system works at 1800 bars, that's 1800 times  the normal pressure at sea level, it causes the diesel to atomize for a better burn, you can imagine what would happen if that fuel was contaminated.

Dirty diesel filters, these are as bad as I have ever seen

Contaminated fuel clogs filters and causes all manner of problems from poor running, smoke and all manner of alarms on modern engines, fortunately the solution is simple, buy your fuel from a reputable source and ensure your filtration system is well maintained, some larger boats have centrifugal fuel polishing systems that spin out the heavy contaminants in the fuel before it goes through the filtration process. Most boats with any size of diesel engine have at least a two stage filtration process, the large pre filters that are usually mounted off the engine, these can have various filtration ratings, 30 and 10 microns are common, a micron is 1/1000 of a millimeter. Some boats have a double pre filter, this is very useful, it allows you to remove a contaminated or clogged filter from service and switch to a second, clean filter, without stopping the motor. The second filter is on the engine itself.

Racor diesel pre filters, double and single type

More than once, the wrong filter size has been installed in the pre filters, so instead of 30, a much smaller filter was installed, it happened to me a couple of times, it's easily done, 2 micron pre filters were installed, it was a 65 foot flybridge boat, when power was demanded of the motors, the filters could not allow enough fuel to flow and so the motors bogged down, fortunately the usual first thing to check is the fuel pre filters, the error was noticed quickly, filters swapped to their correct filtration rating and we were on our way again. I have seen a couple of trawler yachts, the type with ranges measured in the thousands of nautical miles have triple diesel filtration, the last thing you want is your main engine to go down due to dirty fuel when you're crossing point nemo!

Engine cooling or lack thereof is probably the more common issue with engines, marine diesel engines are equipped with closed cooling systems, this means that coolant or antifreeze is circulating around the engine, but, this coolant itself needs cooling, raw water (seawater or lakewater) is sucked up to the motor using an engine mounted pump, is pumped around the engine and makes its way back out via the exhaust. Along the way, the raw water passes through a device called a heat exchanger, the seawater is in one circuit and the coolant in another, hence the closed cooling name, this exchange allows the engine to remain at a stable operating temperature.

The cooling system is critical for engine operation, neglect it too much and it will cause your motor to fail. Apart from not maintaining the raw water pump and its driving mechanism which is usually a belt, the heat exchanger(s) usually have sacrificial anodes, these are blocks of metal (usually zinc), fitted inside the raw water cooling passages of the motor, they get eaten or sacrificed before the other metals inside the heat exchanger, if they are not renewed at regular intervals before they waste away completely, something else will be corroded, heat exchangers are not complicated and operate on simple principals, however, even small ones are expensive, anodes are cheap insurance. On the subject of anodes, sometimes due to irregular wastage of their shape, weak points get created and small fragments fall off the anode and drop into the heat exchanger, periodically, the heat exchanger end caps will need removing and the tubes and pieces of anode removing, it's also a good opportunity to inspect the cooling tubes inside the cooler itself.

The coolant itself should also be changed at regular intervals, the liquid itself has a certain lifespan, after which it will start to lose its properties and not protect the motor as well as it should, consult the owners manual for more information on the service intervals. An important note about coolant or antifreeze (depending upon your part of the world), not all coolants are the same and neither are they all compatible.

Diesel outboards

These motors do not get nearly as much interest or publicity as their gasoline counterparts, I am still waiting to try some, but the few people I know who have personally had experience with them have been impressed, it isn't difficult to imagine why, take the inherently less volatile fuel of diesel, use it´s fuel economy, then, package it into outboards, no more inboard engine rooms and far easier service access, its almost a no brainer and I am surprised they have not got more mainstream sooner.

Maybe the technology and development was slower coming to market, so it has not penetrated as much as gasoline outboards, also, at the time of writing, 300hp seems to be the power output where they are at the moment, although I read a 350 is on the way, compared to other outboards, 600hp is readily available. Up till now I know only of a small amount of diesel outboards in recreational use, more in commercial use, the sales and service centres are increasing so I expect in the next few years we will see more diesel outboards, especially as outboards in general are ever increasing in their popularity and taking more of a market share from inboards and especially outdrives.

If you would like to look at these motors more, the big players right now are Oxe Marine, Cox Marine and Caudwell Marine.

Detroit Diesel 2 stroke inboard engine

Detroit Diesel

No post about diesel engines would be complete without mentioning Detroit Diesel, these motors are a bit unique and special. They have powered so many different things, from landing craft, tanks, buses and trucks as well as boats. The major difference between these motors is their two stroke cycle, although later ones are four stroke, it means they can complete the engine cycle in two engine revolutions as opposed to a conventional engines four, a four stroke cycle is induction, compression, ignition and exhaust, whereas a two stroke combines ignition and compression on the upstroke and power and exhaust on the downstroke, you might be familiar with two stroke outboard motors, although oil does not need to be mixed with fuel in the diesel engine.

Something else that is special, at least to me about these motors is, they were designed to be rebuilt many times, not sure if done this way as part of the build or whether just a happy coincidence, the ability to refinish and fix without just replacement of major components is really important, stops waste and can help ensure a supply chain by exchanging and old component for a rebuilt one, this used to be common practice, you received a discount for returning the core component so it could be rebuilt or refinished.

What ended the widespread use of these motors in new boats was emissions regulations. I used to look after a few boats with these motors, they were a popular installation in Sunseeker and, to be fair, they did not really give any problems. If you are looking at buying a boat with these motors chances are it is an older boat, be aware there seem to be fewer technicians who are able to service them, also check on parts availability, the last time I ordered parts for these motors everything was available without a problem, this may no longer be the case.

Honestly I could write reams about these motors, but probably nothing that has not been written before elsewhere, this then begs the question, would I have a boat with these motors, well, the answer is yes and no and it would depend on a number of factors, I would avoid the electronically controlled motors (DDEC), I would also look carefully at the engine room, this is not aimed directly at DD, but I have seen too many of these motors installed very close to each other, making maintenance an expensive pain. If you see any bottles of multigrade oil on your perspective purchase, ask what they are for, you are supposed to use only monograde engine oil with these motors, this would lead me to think about what else might not have been attended to correctly.

Summary

Whatever diesel engine type you have, look after it, dirty diesel and neglect by not using the engines regularly will drastically reduce their lifespan, mechanical diesels although seen as very old school now are inherently reliable, built at a time before making higher power with smaller engines and trying to extract the most power to weight ratio, I like that, longevity and reliability were paramount. It does have to be said though, technology and materials have come a long way, and unless you are restoring or refitting an older boat, the likelihood is you will be using modern, electronically controlled motors.

Mechanical diesel engines if cared for, should last you a very long time, if you are buying a boat with these motors, it is worth checking parts prices and availability, as well as getting a mechanical inspection.

I hope you have enjoyed reading this post. Please feel free to follow me on social media.