Petrol or Diesel Engines: Which Is Really the Best Engine for You?

May 4, 2015 - 11:27 AM by Samantha Pudney

There has been a long-standing debate on whether petrol engines or diesel engines are superior than the other, and in both camps, devoted users are standing their ground.

If you’re still on the fence about which one is preferable and will give you the best value, read on to learn more about each engine and how they stack up against one another.

Diesel Engines

yanmar diesel engine

In short, diesel engines rely on compression in order to power the engine. The engine provides the power to push the propellers and the rudder while exhaust is directed out of the back of the boat.

The diesel engine’s design is rather similar to the traditional petrol engine design. They both rely on crankshafts, pistons and cylinders. Their biggest difference is the fuel system, with diesel engines being far more complex than a mere petrol engine. Diesel engines are also bigger than traditional petrol engines, which allow them to produce more torque.

These engines also have positive features. For example, they do not produce carbon monoxide meaning that noxious chemicals won’t seep into the cabins or out of the back of the boat. They also produce excellent torque and have a rather long life expectancy. Their running costs are often very low, and the fuel has a higher ignition temperature.

Keep in mind that diesel engines weigh more. If your boat is smaller than 8 metres, a diesel engine might weigh it down too much and dramatically reduce your speed and its power.

Petrol Engines

petrol engine

Like a car engine, petrol need a spark to get started, rather than compression like diesel engines. Their horsepower can range anywhere from 90 to 1000, and they’re far lighter than diesel engines. The drive system is also less complex, which means there is less maintenance work to do.

For the most part, petrol engines are cheaper to run, though this will depend on how fast you want to go and how long you want to use your boat. This is really only an issue if you’re operating your motors at or at least near the Wide Open Throttle all day. By using a low throttle instead, petrol engines consume far less than most other engines.

Their biggest advantage is easily the amount of noise and vibrations they don’t make, which is great for boaters who intend to leisurely sail around harbours and close to the shoreline.

When petrol engines were first used as inboard engines, there were several major dangers that accompanied them, such as sudden explosions. This is because the engines did not have sealed carbines, fuel injection systems and electronic ignition set-ups. Now modern petrol engines have these features and are much safer so long as owners are diligent about upkeep.

So Which One Should I Buy?

To properly answer this question, you must first ask yourself a few other questions to determine what exactly you need from your boat and what you plan to use it for. Check out the list below:

  • How big is my boat? Diesel engines are quite heavy and shouldn’t be on boats smaller than ten metres.
  • How often will I be using my boat? Think of this in terms of hours rather than days.
  • How fast do I plan to go? Some boats are designed to run at particular speeds.

Now that you have those questions answered, check out these facts below to determine which type of engine will help you meet your boating needs.


Smaller boats will definitely benefit more from a petrol engine, no doubt. A diesel one will only weigh your boat down. However, if you have a bigger boat, a diesel engine might give it more of a boost, though it will be louder than the petrol engine.

Time Spent Boating

Try to calculate a rough estimate of how much time you plan to spend boating this year or season, depending on your location. Is this a weekend hobby or do you plan to sail to New Zealand, India or even across the Pacific Ocean to the United States?


A study conducted by Mariner Cruisers found that most owners used their boats for about 150 hours the first year they owned it and then fifty hours each year after. If you plan on spending less than 100 hours per year sailing, petrol might be a better option, especially if you plan on tottering around your local area and harbour.

Also, be sure to take into account the number of petrol stations nearby or other ways of obtaining petrol. On the River Thames in England, for example, there are no petrol stations. This means that petrol users will have to find a method of transportation, such as a van, as well as a funnel and several 20L cans in order to transport the fuel. Where you live now may have ample petrol stations dockside, but be wary of places that might not.

Need for Speed

Sailing is supposed to be gentle and relaxing. The true joy comes from enjoying the trip out there. However, if you’re planning a long journey to other countries and ports, time may be of the essence, and you might need to get there quicker.

Though petrol engines may use less fuel at low RPM, this is not the case when you need to go faster. A petrol engine will consume more fuel because it has to work much harder to keep up with a diesel engine, which uses less fuel to get you from Point A to B at a faster time.

So before you decide to buy a boat or an engine, ask yourself honestly: how often do you sail, how hard to you need to work the motor and how far from home do you plan on sailing?