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How To Choose The Best Engine For Your Boat

We are lucky enough to live alongside a coastline on the Indian ocean and some of the world’s best beaches. So it’s no wonder that more and more people are splashing out on a new boat instead of a new car. If you’re looking at taking that leap, there are several things you need to take into consideration including what marine mechanical solution is best for your boat. As a Mobile marine diesel mechanic, I have highlighted some the pros and cons of diesel versus petrol power and I’m here to help you choose.

Diesel is indeed more expensive and heavier than petrol so it may make sense to go with a petrol engine instead, right? Well maybe. You see, apart from the cost of fuel there are other things to consider such as the size of your boat. Smaller powerboats of 30 to 35 feet will usually only be available in a petrol engine. The bigger the size of boat, the more choice you have. However once you hit the big time and look at a 45 footer, the displacement weight requires the torque and horsepower that only one fuel type can supply and that’s diesel.

Power curves also come into play with Marine diesel engines too. Sure petrol has plenty of power to run adequately but diesel is faster and far more responsive. But the truth is that performance differs from one type of marine mechanical solution to another, dependent on the boat, size, engine torque and horsepower curves. There are decibels with diesel engines being more noisier and as a Marine diesel mechanic, I can tell you that part of the cost of having a diesel mechanical engine is enhancing the engine room with soundproofing.

Top tip! Apps on your smartphone can let you perform a sound check so you can be sure that the excess noise doesn’t detract from the quality of your recreation time on board.

Next we look at fuel prices. Here in Perth, fuel prices have gone haywire, though we do know that diesel fuel does supply more energy potential and is more efficient per gallon than petrol.

The Hull

The hill is also another factor. A planning hull, a displacement or semi-displacement hull and how it is loaded and typically runs will also determine the Marine mechanical solution for you.

Resale Value

Yes you are looking to buy a boat so it may seem silly to already start thinking about the resale value but it is just one more factor to help you figure out the best engine for your boat. Take a look and do some research on the sell price of boats in the 35-40 foot size range and the engine types. In general however, diesel fuelled boats will tend to sell quicker and will nearly always command a higher selling price and this in part is due to customer perceptions that diesel engines are generally more reliable and safer.

Maintenance Costs

My role as a Marine diesel mechanic has seen a lot of changes in the past decade. While marine diesel engines are known to be easier to maintain in general, engines are, modern engines are now computer-controlled which contributes to cleaner-running engines and reduced maintenance for petrol engines too, meaning the maintenance cost difference between petrol and diesels engines are minor. They will both need oil and filter changes and fuel/water-separating filters, cooling system anodes, engine coolant, and water pump impellers will need replacing regularly. Overall, you won’t see that much difference in maintenance cost over the average period of ownership.


There aren’t any significant savings in annual insurance costs with diesel power versus petrol power, although there were slight differences that had more to do with higher replacement costs for diesel-powered boats, so all in all, this isn’t a major deciding factor.


While diesel boats are known to be safer than petrol boats, new boats regardless of mechanics offer as much safety as possible, at least until the boats get to be 15 to 20 years old. At that point, petrol fuel systems start deteriorating and failing hose clamps and fuel hoses will need replacing.  Even metal fuel tanks can start to corrode so an annual inspection of all petrol fuel systems is highly recommended.

Life Expectancy

New engines are providing a lot more power out of smaller-displacement diesels to save weight. The engines are turbocharged or have both superchargers and turbochargers installed which results in more stress on the engines so it’ll be difficult for instance to find a  diesel offshore fishing boat that’s getting more than 1,500 to 2,000 hours of run time on its engines!

For the average diesel-fuelled sport-cruiser however, running conditions will obviously be less strenuous. Diesel engines will last longer than petrol engines by a long way as long as routine maintenance is performed.  However in the event of a major failure, replacement of the diesel will of course outweigh the replacement of a petrol engine by a significant amount.

In short the marine mechanical solutions for your boat will depend on the size of boat, what you plan on doing with it and how long you intend to keep the boat for. The best thing to do? Try the model boat you’re considering with both a diesel and a petrol engine and see how it feels.

Estimate the number of hours per year you’ll be running the engine and remember, you’re going to need to get a really good amount of usage on your boat to ensure you get close enough to recouping the difference between the cost of petrol and diesel engines.

If you want personalised advice, search “Diesel mechanic near me” and Dtech Contracting will provide all the help you need.