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.



When does outboard power become ridiculous?

Outboard engines have their place and uses. However, a trend over the last few years has been to simply add more outboards to a hull in order to give it more power. No longer are there simply triple or quad outboard installations, but sometimes even five, six or more.

At what point does simply adding more outboards become pointless?

When the costs outweigh the benefits.

The vessel pictured is a pretty well-known photograph of a drug-runner caught in the English Channel (a “scandal” in the UK marine industry at the time). It essentially is engine and fuel tank. Now, most people are not buying boats for smuggling, but are intending to use the vessel over an extended period of time. What does adding extra engines actually do as far as performance?


  1. Added weight (not just the engine, but all equipment, such as mounts and the weight of extra fuel).
  2. Added drag.
  3. Reduced maneuverability.
  4. Reduced safety (often, the hull was not designed for such applications)
  5. Huge increase in fuel costs.
  6. Reduced running time and range (unless larger fuel tanks were designed or installed)
  7. Greatly increased maintenance expense
  8. Difficulty in ventilating the props.



  1. Greater power.
  2. Greater acceleration.


Note that the negatives are pretty big, compared to the positives and their associated costs. Of course, these negatives can be minimized by using diesel inboard engines.

Should a vessel be equipped with two 250 hp outboards, or a single VGT 500? What about instead of three 300 hp Mercury Verados, two VGT 450s?

Unless the vessel has absolutely no room for an inboard, the inboard option will win every time.

  1. Weight: Two Mercury Verados weigh 586 kg. A single VGT 500 weighs 515 kg. Even with gearbox and drive, the weight differential is only around 100 kg.
  2. Drag: Fewer engines mean less drag. All of the time.
  3. Maneuverability: Even numbers are more maneuverable, due to less torsional pull. However, the reduced drag and greater number of propulsion options mean that a single inboard will be as good as or more maneuverable than multiple outboards.
  4. Fuel: No contest. A single diesel VGT will save enough money to pay for the differential in price very, very quickly.
  5. Range: Likewise, the range can be longer, with smaller fuel tanks.
  6. Maintenance: Though an inboard diesel, depending on engine compartment and configuration, is less accessible, it will have a far higher life cycle and require less maintenance and access.
  7. Acceleration: Multiple outboards can accellerate very quickly. But guess what. A Marinediesel VGT engine, designed for high speed craft, will accelerate faster.
  8. Service life: A VGT engine will last as much as five times longer than even the highest quality outboards.

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.


Maintenance Tip of the Week: Diesel Spill 06/22/2015



Maintenance Tip of the Week – Diesel Spill

If you spill diesel fuel in an engine room, the smell can quickly become quite strong. Scented dishwashing liquid (a degreaser) can help remove the smell. For some reason, a mixture of baking soda and Coca Cola dabbed on the spot can also remove the smell.




Choosing the Right Engine



As an engine manufacturer, MarineDiesel would love to be able to answer the question, “Which engine should I choose for my project?” with a resounding “MarineDiesel, of course!” every single time. However, that is not the correct answer to give. Different engines have different strengths and weaknesses, and ours are no different. We often get requests to quote where our engines are simply not an appropriate match for a project. Sometimes, people are just price shopping, matching horsepower to horsepower, and sometimes a new project pops up where the shipyard does not have a lot of experience.

When determining the engine to choose, price should be among the last crieria that should be considered. There are far more important questions to ask:

  1. How will the vessel be used? Our engines tend to focus on fast boat applications. They are normally not a good match on tug boats, for instance (Though sometimes, occasionally, they are suitable).
  2. How much space is available for the engine? Smaller spaces require smaller engines.
  3. Is noise a problem? Engines are tested for noise when manufactured. Noise can be controlled through both silencing and insulation, in addition, yet those items also have costs in space and money associated with them.
  4. Is vibration a problem? Some engines, such as our VGT Series, produce much less vibration than inline models, due to their physical characteristics. Additionally, there are aftermarket ways to control vibration, like the use of different mounts or couplings.
  5. How capable is your maintenance team? Some engines are more complex than others. Some require a higher level of skill to maintain.
  6. Price. Price is important, and does play a role. However, consideration also needs to be given to the cost of spares, service, and training.
  7. Life Cycle / Rating. An engine used 2,000 hours per year needs a longer life cycle than an engine used for recreational purposes.
  8. Service network. Some engines may fit all criteria, but there is no service in your country available. Engine maintenance gets expensive very quickly when performed across continents.
  9. Warranty. How good is your engine’s warranty? Some manufacturers have better warranties than others.
  10. Fuel consumption. Fuel costs, on average, exceed 60% of any engine’s operating cost. Cost savings are significant over time.
  11. Performance expectations. You need to have proper calculations made with bona fide data: Not just guesses. Horsepower and torque requirements can vary drastically with small differences in hull design.
  12. Emissions requirements. This can be important. Laws and regulations vary widely between regions / nations.

We realize that choosing an engine is complicated. Contact your local MarineDiesel dealer for personalized assistance on your project.





Are there quality differences in diesel fuel?


Fuel quality is a topic that is frequently discussed on this blog. Fuel is such a critical factor in engine performance and reliability, that is why we give the topic so much attention.

Is there a difference between brands in terms of fuel quality? In other words, is there a difference between marine grade diesel produced by Shell, versus Exxon, versus any other brand?

The answer is, in theory, yes, but there are other factors that are far more important. The primary difference is the additives each producer blends with a specific brands of fuel. For instance, Exxon may add one proprietary additive to improve combustion and Shell may add their own proprietary blend.

The Cetane Number is also an indicator of fuel quality. The Cetane Number is an index of the time from injection to compression. High speed diesel engines typically perform better with higher Cetane Numbers, typically over 40.

What is far more important from an engine manufacturer’s perspective is the quality of fuel that the customer receives at the bunker. Fuel quality can vary widely based on storage conditions, infrastructure conditions, regions of the world or even within one region. These factors are often independent of brand, and out of the refineries’ control.

What is certain is the following: All major fuel producers in the world comply with strict ISO standards regarding fuel quality. When the fuel leaves the refinery, it is effectively guaranteed to be of a specific quality. Problems with quality normally arise much further down the supply chain.

All marine fuels are required to comply with the latest ISO 8217 standards, effective from June of 2012. Additionally, in regions where ULSD is mandated (most notably North America and Europe), sulfur content is further restricted and the fuel is in compliance with EPA and EU rules:

  • 15 ppm: Sulfur limit of 15 ppm (ULSD) becomes effective in June 2010 for nonroad fuel, and in June 2012 for locomotive and marine fuels. ULSD has been legislated for nonroad engines to enable advanced emission control systems for meeting the Tier 4 nonroad emission standards.

For the ISO quality standards, see the chart below:


DMX is the normal standard for marine use.



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.


Use it, or lose it


Time is not your friend when it comes to marine diesel engines. Diesel engines, by their nature, operate best when they are started frequently, and operated at WOT (wide open throttle) every once in a while. In a way, this is counter-intuitive, since diesels are often discussed in terms of life cycle, how long they will last before overhaul, and sheer number of hour used. However, a long time between overhauls does not mean much if the engines simply sit in storage or if the vessel spends most of its’ time tied up at a dock.

Diesel engines are complex pieces of machinery. Routine starting and operation keeps internal components lubed up and free from rust or deposits. Additionally, seals and gaskets take time to properly seal, and operating the engine makes good, tight seals. Additionally, diesel fuel degrades and becomes contaminated over time. Routinely starting and operating the engine keeps the fuel fresh, and fuel lines clear with periodic fuel flow. This is why MarineDiesel has a very specific winter storage procedure for owners to follow.

Commercial and government vessels typically have very heavy, continual use. Indeed, we have seen some of these vessel types operate up to 3,000 hours or more per year, under the harshest of conditions.

The problems associated with non-use are typically experienced on recreational, or pleasure, boats. They simply do not get the high use that commercial vessels. (Sometimes as little as 50 hours use per year). This is why it is important that pleasure boat owners start their engines, minimally, at least monthly, letting them run at WOT at least for a little while. If this procedure is followed, the engines should last as specified by their rating, giving years of reliable use.



Ski Boat and Parasail Boat Engines


The market for commercial marine engines is quite varied. There are dozens of different types of commercial vessels and uses, each with their own specific performance requirements.

One market niche where MarineDiesel engines are extremely competitive is the ski boat and parasailing boat market. These boats have very specific engine power requirements. Commercial, yet recreational also, these vessels need to be operational on a seasonal basis (usually), and every minute they are not operating can cost the owners thousands upon thousands of dollars in opportunity costs that are lost forever. They often use gasoline or petrol engines, and the Marinediesel engine’s compact size gives the operators a high torque, lower operating cost, diesel alternative.

Additionally, ski boats and parasail boats typically have highly compact engine compartments and need to minimize weight. The VGT Series is the most compact engine in its’ class on the market. In most cases, it is the ONLY marine diesel engine that can even fit into these types of vessels.

Ski boats and parasail boats require a torque curve that gives the optimal power at the lower RPM range for rapid takeoff, decreasing in need after the vessel is planning (This is why they often use gasoline engines, designed originally for automobiles). The NIRA ECU used by MarineDiesel allows us to optimize the performance specifically for these types of operations, giving the operator the torque that is needed, when it is needed. Add in the lower cost of diesel fuel (usually) and the much longer life cycle of a diesel engine versus a gasoline engine, and the best decision becomes immediately clear: Marinediesel’s VGT Series.



High Performance Pleasure Boating


Marinediesel is known for manufacturing high performance engines rated for government or military use and the extreme conditions under which these types of vessels operate. You may think, “Oh, I don’t need over-engineering for my boat that I only use on the weekends”.

However, what if you could put our engines in your pleasure boat at around the same price as other engines?
MarineDiesel’s VGT Series makes this possible.

Our engines are designed to take high punishment, operating in the roughest seas and in conditions that simply destroy engines made by our competition. We are the lightest, most powerful engine brand in our class.
Most pleasure boat owners use their engines under 100 hours annually. Typically, engines rated for recreational use will last 750 hours before requiring a major overhaul. Compare this to the 2,500 to 3,000 hours that MarineDiesel’s VGT engines will last. Quite possibly, the engines will last much longer than the average lifespan of a GRP hull of 20 years.

In other words….

The MarineDiesel VGT Series is the last engine you will ever need to purchase for your boat!
All the while giving you the level of performance demanded by some of the most rugged military craft on the market.

Don’t just take our word for it, though. Contact your local MarineDiesel distributor or vessel manufacturer and compare for yourself. We are standard or optional equipment on dozens of major boat brands manufactured all over the world. Ask to see how Marinediesel can give you high performance, long life, and reliability at a reasonable price.