Why waste money on an outboard? The Marinediesel VGT Series makes them obsolete!

Outboard engines are usually a complete waste of money for commercial and government vessels.


Quite simply, they are not designed for anything other than recreational, or occasionally, racing use.

Outboard engines are usually merely petrol car engines turned vertically and connected to a modified automobile transmission. They were designed to provide the torque that an automobile requires in order to operate efficiently. The problems start to arise with respect to torque: Boats are under far higher levels of resistance than automobiles, particular at lower rpm ranges. So, many companies have tried to use diesel engines in outboards, rather than gasoline engines. What was the problem? Simple. The gearbox and drive systems were not designed to withstand the amount of torque produced by a diesel.

There is an old saying in the marine industry: “Horsepower sells boats, but torque actually moves them”. A quick glance at the marketing materials produced by outboard manufacturers quickly confirms that fact: Virtually none of them mention torque or show torque curves.

Some advantages of a diesel inboard over gasoline outboards:

  1. Diesel fuel is normally cheaper than gasoline in most markets. For example, in Australia, August 2015, retail price of diesel is A$1.29 per liter average, petrol A$1.34. In some countries the differential exceeds 20%. For instance, during the same period in Thailand, diesel averaged US$0.64 per liter and petrol US$0.93.
  2. Diesel engines always consume less fuel than gasoline engines. For instance, a Mercury Verado 350 consumes a whopping 353 g/kWh at full throttle, compared to 221 g/kWh on the Marinediesel VGT300. This equates to over 1/3 higher consumption. At cruising speed of 5,000 rpm on the outboard, the fuel consumption drops to 190 g/kWh, but the power produced decreases by over 1/3, netting just over 220 hp. The VGT300’s cruising speed of 2,800 rpm yields a fuel consumption of 195 g/kWh, but still producing nearly 280 hp.
  3.  As far as torque is concerned, virtually no comparison is possible. The outboard produces barely 400 Nm of torque, under a drastic bell curve, whereas the VGT 300 produces nearly 600 Nm of torque along the majority of the rpm range. A huge difference in actual work performed by the engine.
  4. Gasoline outboards have a MTBO of under 400 hours, light recreational use (all of them). A diesel inboard will last up to 3,000 hours MTBO. You could overhaul an outboard five times before needing to overhaul the diesel.
  5. The outboards are lighter. 303 kg versus 515 kg. This is reflected in their lower torque produced.
  6. However, space is less of a constraint. The Mercury Verado 350 is less than 100 mm smaller on all dimensions. A quick look at the photo above shows a transom width of about 1 meter. The VGT engines will require approximately 300 mm more length, and no extra width. A mere 300 mm extra height is necessary. In other words, on the boat picture, two VGT engines WILL fit.
  7. Outboards cost less to purchase. MSRP on the Mercury Verado 350 was US$32,000 in August 2015. The VGT 350 MSRP was US$37,000. However, given the fuel cost and consumption differentials, this small difference in acquisition cost quickly disappears.
  8. Gasoline is far more explosive than diesel. The inboards are much safer.
  9. Diesel engines have higher maintenance costs, but require much less maintenance.

As is evident in the points above, a strong case can be made for equipping your vessel with the Marinediesel VGT Series instead of outboards. The cost differential at acquisition is minimal, and the diesels far outperform outboards in nearly every instance. In particular, on the higher horsepower outboards, the price differential starts becoming significantly less.

Finally, in the picture above, twin Yamaha 200 hp outboards are pictured. A single VGT 400 or VGT 450 will outperform those two engines, lessening the price differential, even after gearboxes and drives are taken into account on the VGT engines.



VGT: THE diesel alternative to outboards

Outboards are common on small, high speed craft. Indeed, on some vessel types, they are often though of as the “default” propulsion method.


  1. They are cheap.
  2. They are easy to maintain.
  3. They provide “pretty good” speed.
  4. They do not take up much space.
  5. They are lightweight.
  6. A row of them, side-by-side “looks” fast and impressive.

However, outboard engines have some serious disadvantages and limitations:

  1. Outboard engines are usually gasoline automobile engines that are mounted vertically to a gearbox and drive system as a single unit. The forces generated by these engines are vertical, rather than horizontal, resulting in a substantial loss of power and a drastic increase in wear.
  2. Gasoline (petrol) is an explosion and fire risk, especially with government vessels or those used in the offshore industry. (Diesel is a much safer fuel)
  3. Gasoline is usually more expensive than diesel. Additionally, gasoline engines always consume fuel at a higher rate than diesel engines. (In some markets, the differential is as much as 50%).
  4. Outboard engines have a life cycle that is usually no more than a few hundred hours, at best. (You can  easily replace an outboard five times before needing to rebuild a VGT engine… Not so cheap now, eh?)
  5. Outboard engines are, by their design, limited in the number of propulsion options (You get what you get. With a VGT engine, you can use jets, surface drives, a variety of stern drives, or traditional shafts.)
  6. Diesel engines provide far more torque than outboard engines (Outboards cannot even come close).
  7. The vessel will always perform better with a VGT engine and proper propulsion system. ALWAYS.

The Marinediesel VGT Series of engines was designed to be the lightest, most powerful engines in their class. Our compact size and high power output make them an ideal alternative to the use of outboard engines. The VGT will, quite simply, fit where other engines may not.

Vessels can be equipped with Marinediesel inboard VGT engines at only a slightly higher cost than equipping the same vessel with large outboard engines, and that slightly higher cost is recouped very quickly in a much longer service life and the substantial fuel savings received. In fact, on larger outboard vessels, the use of outboards for propulsion is often equated by simply flushing money down the drain. They always cost more in the long term. In fact, many of our customers refer to outboards as “throwaway” engines. They run them full throttle until they simply break, and replace them with a new engine.


This “ease of replacement” and “ease of repair” is very much an illusion. The Marinediesel VGT Series will last up to five times longer than the average outboard before requiring an overhaul. Additionally, our remote mounting options give the VGT Series an ease of maintenance that approaches even the best designed outboard.

Additionally, the higher power and torque give a much better level of performance and control than an outboard-equipped vessel. Outboards, by design, are limited in the amount of operational control that they can provide, particularly regarding trim. A well-designed propulsion package with inboard engines will give a higher level of control and speed than even the best outboards on the market.

Finally, outboard engines are external, and thus, noisy by design. They are very difficult to control noise, and are often impossible for effective noise control.

If you want to look into the feasibility of using our VGT engines instead of outboards, and experiencing the meaning of true performance, Contact Us or your local Marinediesel Distributor for a quote today.


What happens if you put gasoline into a diesel engine?


Don’t do it.


Don’t try it.

At best, you will ruin your engine. Quickly.

At worst, you could start a fire.

Why would someone try this? There is normally no financial incentive, since gasoline, or petrol, is normally more expensive than diesel. When this situation happens, not too commonly with marine engines, in our experience it is a mistake when filling the tank. Somebody grabs the wrong hose.

But, you may ask, if diesel and gasoline both are distilled from petroleum, why is that a problem?

The answer lies in the way ignition of the fuel is made. Gasoline uses a spark ignition system that, when the fuel is mixed with air at the proper moment in time, combustion occurs.

On the other hand, diesel engines are based on the principles of self-ignition (there are no spark plugs). The heat from compression is what causes ignition, rather than a spark. When gasoline is introduced into the engine, it might ignite in the combustion chamber, it may not ignite, or it may ignite at the wrong time, possibly even within the exhaust system. The best case scenario? You have ignition at the wrong time in the cylinder, ruining the cylinder, piston, and cylinder head. Why is this bad? You have just introduced an explosion in a part of the engine that was never intended to contain an explosion.

Unfortunately, when such mistakes occur, there is normally very little recourse other than to drain the fuel system, and repair the engine, with a complete rebuilding usually required. That is, if you have not blown up the boat.


10 Facts About Diesel



There are many myths and misconceptions in the marketplace regarding diesel fuel and diesel engines. Indeed, the debates can be endless, and every engineer and naval architect has their own beliefs. Some may be true, while others are no more than mere wive’s tales. Today’s article discusses some interesting facts about diesel fuel and diesel engines. Tomorrow’s article will address some of the myths.

  1. Diesel fuel was named after the diesel engine. NOT the man who invented the engine (Rudolf Diesel)
  2. Diesel fuel, unless further refined, is a high pollution fuel. Further refining, under emissions regulations, has produced Ultra Low Sulphur Diesel (ULSD), which is one of the cleanest fuels in the market. Thus, modern diesel fuel is usually cleaner than the gasoline with which it is often compared.
  3. Diesel engines are always more fuel efficient than gasoline (petrol) engines.
  4. Diesel does not evaporate (as does gasoline), but it does degrade more quickly over time.
  5. Diesel engines are more durable and have a longer life span than gasoline engines.
  6. Diesel engines require more maintenance in the marine environment than gasoline engines.
  7. Diesel engines tend to be more expensive at purchase than gasoline engines (though the longer life cycle means that they are usually cheaper over the long term).
  8. Diesel engines produce more heat than gasoline engines. The nature of diesel fuel means that it has a BTU output, and thus produces more heat.
  9. Diesel fuel is usually the same price or cheaper (even ULSD) than gasoline at the refinery. The price differentials are usually more related to local taxation, rather than the cost of production.
  10. Biodiesel is still diesel. Though it is refined from vegetable products, rather than petroleum, biodiesel still must meet strict standards for quality and energy content. Nearly all marine engine manufacturers allow the use of biodiesel within their warranties.




Diesel versus Petrol: What’s the advantages and disadvantages?

We occasionally get asked by our customers whether or not they should put a diesel engine in their vessel, or a petrol engine. As with everything else in life, there is no single “right or wrong” answer. We manufacture both types of engines, so we are truly non-biased in our opinion. The answer is, “It depends.”

Ask yourself these questions:

What is the purpose of the vessel?

How will the vessel be used?

What are the emissions regulations in my area?

What is my budget?

These all have an impact. So, to make things easier to break down, we will use diesel as a starting point, listing advantages and disadvantages versus petrol.


  1. More efficient combustion versus petrol. Diesel engines have a much higher output of torque than petrol engines. Given the same horsepower on two engines (see below), the diesel will provide more work for the fuel spent.
  2. Much longer life cycle that petrol engines. As much as three or four times longer. Petrol engines work “harder” to produce the same power, and are more complex, thus needing more frequent maintenance.
  3. Diesel is cheaper than petrol (At least in most of the world).
  4. Much lower fuel consumption.
  5. Petrol has a greater risk of explosion and fire. Requires greater ventilation.
  6. Diesel engines produce much less heat, and are cooled more efficiently. Petrol engines can require substantial cooling systems at greater cost.



  1. Diesel engines are usually more expensive than petrol engines, often up to twice the price.
  2. Diesel engines produce more smoke with dirty fuel (Though ULSDF required in Europe and the USA is actually cleaner than petrol).
  3. Diesel fuel breaks down rapidly. If engines will sit for long periods of time, the fuel will need to be stabilized or drained.

The pictures below illustrate two MD engines’ power and torque curves, showing a big difference in torque, but producing the same horsepower.

petrol 6-2

MD VGT 400 diesel power and torque curves.

MD VGT 400 diesel power and torque curves.

Can I use a Nitrous System in a Diesel Engine?


Yesterday, an interesting article was published on Yahoo Automotive regarding the use of Nitrous Oxide Systems (NOS) in gasoline engines, and whether the increased horsepower was worth the expense.

Nitrous is one of the most divisive topics in the world of performance driving. Some think that it’s a sure-fire way to turn any engine into a hyper-powered brute. Others dismiss it or claim that it’s an excellent way to destroy your car. As with most things, however, the truth is in between the extremes. To see why, let’s take a closer look at the subject.


It all Comes down to Oxygen

Try to fire up your barbecue grill in the vacuum of outer space and what will you get? Nothing. That’s because oxygen is necessary for combustion to occur. Without this vital gas conventional engines can’t function. That’s why the Apollo astronaut’s moon buggy and the Mars rovers both ran on batteries.

The more oxygen and the more gas you can cram into a cylinder, the more power you’ll get out of an engine. But it turns out that earth’s atmosphere is only 21% oxygen. This fact is vital to our continued existence, as pure oxygen would make the planet blow up as soon as someone lit a match. In terms of automotive performance, however, it puts a limit on how much power can be created using plain old air…

Here’s a link to the complete article

MarineDiesel specializes in diesel engines for high performance vessels. Would a Nitrous system improve the performance on our engines?

The answer is, “Possibly”, but mostly “No”… And, you will certainly void your warranty if you try it.

There are a very few high performance diesel engines in the marine market, almost all designed specifically for racing, that have NOS installed. In virtually every case, these engines were intended to be used under race conditions, with very short life cycles, and for very short periods of time.

Modern diesel engines are designed with a turbocharger and electronic controls that already bring the optimum amount of oxygen into the combustion chamber. Altering this mix, with a NOS installed, does several things:

1. Increases the exhaust temperature.

2. Produces excessive smoke (The fuel mix becomes too rich)

3. Increases the heat in the cylinders, producing excessive wear on the pistons and rings.

4. Increases the heat in the turbocharger.

Now, in a diesel engine with a standard turbocharger, not VGT, the fuel mix is able to be manipulated, just as with a gasoline engine. With our VGT engines, we have already optimized that mixture, and the addition of Nitrous simply results in an over-fuel state.

Therefore, though you would receive a very little amount of additional power from the engine, you would seriously decrease its’ service life, and greatly increase the cost of ownership, especially given that you have just voided your warranty.

So, the short answer is, “Don’t Do It!”





Interesting article about diesel / gasoline hybrid



Some interesting research at UW:

Five years ago we first heard about a Caterpillar diesel engine located at the University of Wisconsin-Madison, that had been modified to run on an unlikely-sounding mixture of diesel and gasoline. Not only did the one-cylinder engine work, but it was more efficient than pure-diesel or pure-gas engines at converting the chemical energy of fuel into motion. Sitting in a basement lab, however, isn’t the same as experiencing use in the real world. That’s why students at UW-Madison, led by Prof. Rolf Reitz, have now put another diesel/gas engine into a 2009 Saturn.


To read the complete article on Gizmag



Ask Professor Diesel – 05/26/2014


This week’s question comes from John in the USA:


Professor Diesel:

I know that diesel engines can run on many types of fuel, what would happen if I try and use gasoline?



NEVER use gasoline in a diesel engine. At best, permanent damage will result. At worst, explosion or fire. Some diesel operators will add a little gasoline to diesel when preparing for storage over extended periods, as this can help in starting (MarineDiesel does not recommend this practice and it will void your warranty if you try it). NEVER more than 10% of total volume. The engine will run, but it is safest to drain the fuel and lines if gasoline has been added.


If you have a question for Professor Diesel that you would like answered, please fill in the form below:

[accua-form fid=”9″]