What type of engine to choose (gasoline or diesel) - modern yachtsmen argue about this, often citing arguments that turn out to be myths, nothing more. The first myth concerns safety - they say that diesel engines are fire and explosion safe. This opinion is often based on the impressions of yachtsmen who had the misfortune of witnessing fires on yachts of a significantly lower technical level than we have today, which occurred 30 years ago. The state of affairs today is such that gasoline engines of modern assembly are very safe, and the chance of a fire on the water due to them is even lower than the chance of getting into a plane crash on the way from warm resorts to home. But from the point of view of explosion protection, diesels are safe, since diesel fuel vapors are not prone to spontaneous ignition.
Of course, the exhaust gases of gasoline engines contain a large amount of carbon monoxide, but most often the danger is not the main engines on the ship, but the gas generators. The reasons for the danger are carbon monoxide leaks due to imperfect exhaust pipe systems or the concentration of gases behind the stern of the vessel, where a zone of reduced pressure is created when air flows around the yacht's hull. And if you prefer regular overnight stays with the electricity generator on over day stops, we strongly recommend getting the diesel model. Diesel engine exhaust contains less carbon monoxide, but sulfur dioxide is present, which contributes to the manifestation of symptoms of "seasickness" and the occurrence of headaches.
The second myth is the durability of diesel engines. This opinion of the majority is due to the reputation of "eternal" diesel engines, as well as diesel generators on ships, earned by land-based long-range tractors. Indeed, diesels operate continuously on land and sea commercial vehicles, generating thousands of hours without overhaul, without shutdown, or with very rare stops for inspection and maintenance.
Specialists-mechanics know that it is precisely this continuous operation of the diesel that they owe such durability. On pleasure craft, the diesel is switched on from time to time, and in the periods between operation, corrosion appears on the contacting parts of the engine, leading to accelerated wear of all its components. In most cases, the failure of a diesel engine on a yacht is caused by corrosive wear and lack of proper maintenance, so there is no question of durability.
The next myth about diesel engines is their unprecedented efficiency. This delusion is alive due to the memories of older yachtsmen, in which diesel fuel cost three times cheaper than gasoline, but today its cost is only 10-12% lower than gasoline. In addition, the cost of parts for diesel engines is much higher, and diesel service technicians ask for their work on average 40-50% higher wages than specialists working with gasoline units.
Another myth is the preference for engines with lower motorcycle counter readings over motors with longer operating times. The misconception is based on the belief that the engine has been running without extended downtime. But if the motor counter turns on at the moment the ignition is turned on (and turns off with it), then the yacht's lifetime flows continuously. This means that in practice, old diesel engines with a low number of engine hours are often observed, which indicates a longer downtime, leading to wear due to corrosion. And for an engine of the same age, but constantly working and with a large number of worked hours, the wear will be much weaker - it will be in better condition. It's all about the parts of the cylinder-piston group - and they do not like downtime and corrode under the influence of moisture condensing in the cylinders from the air. As a result, powertrain repairs are expensive.
Another misconception is that the time of the uninterrupted operation of a diesel engine before overhaul is equal to several thousand engine hours. This is fundamentally not the case - the average operating time of diesel engines of yachts before overhaul is 1500 hours. If this figure seems underestimated to you, compare it with the service life of a gasoline engine on yachts, which is, on average, 900 hours.
Small in weight, forced diesel engines are less durable, since the likelihood of deformations and microcracks depends on the thickness of the cylinder casting (the thicker the casting, the less deformations occur) and premature engine wear. Fuel re-enrichment is also important - if you purchase a motor from a passenger car (not adapted for continuous operation at rated power) and make it continuously work on a boat at high power, then you will be dealing with a noticeable increase in fuel and air consumption. This factor is true for both gasoline and diesel engines. The most common culprit for the failure of high-speed high-powered engines is piston breakage, coupled with valve failures, working “for wear”. Therefore, in order to increase the resource, automotive power plants must be radically rebuilt before being installed on yachts.
According to the specialists 2yachts, the choice between diesel and gasoline engine becomes obvious when the mass and dimensions of the yacht reach a certain features - conventionally, you can take its value in the region of 8 tons and 35 feet. Diesels have a lot of torque, delivering the lion's share of power at medium revs, and are better suited for heavy boats. At the same time, gasoline engines show peak power at maximum rpm, leaving no reserve of power in case of increased loads. On small yachts, the advantage of diesel engines in the form of resistance to increased loads is lost. Diesel engines develop power similar to gasoline units with significantly lower fuel consumption, but the high cost of their maintenance negates this superiority.
In addition to the above, consider the crankshaft speed and engine weight. The fact is that higher-revving diesels are less durable for a number of reasons. Low-speed diesels are more durable, but if you make the "slow" engine run at higher speeds, all its benefits disappear. Light, low-speed automotive engines in marine applications cannot perform as good mileage between repairs as they do in their normal operating conditions. The loads on the ship on the water and on the car on land are not comparable. Lightweight automotive diesels are simply not capable of pushing a massive vessel in a water environment on a continuous basis. It does not matter if the engine is diesel or gasoline, depending on the increase in travel speed, the cost of fuel and repairs will increase.
A pair of diesels of not the largest size on one yacht can weigh a ton more than two gasoline engines for the same yacht. On a fast vessel, excess weight will result in a noticeable decrease in vessel speed. Without losing sight of this factor, it is reasonable to consider the limit where it makes sense to use a gasoline engine type. Therefore, you can think about installing it, achieving a given speed with a lower power of the power plant, since it will be easier for the yacht to move around this way.
One significant advantage of the diesel engine will win over fans of leisurely sailing over long distances - it is low fuel consumption and, as a result, increased cruising range.
The mistake of many yachtsmen is the belief that while saving on fuel they benefit 100% from the total cost of operating a diesel engine. Suffice it to calculate that with an average diesel usage time of 150 hours per year, the owner is unlikely to get an advantage in fuel economy for diesel engines costing $ 20,000 or more. Even with the most optimistic distribution of diesel savings of about $ 0.1 per liter, you would need to use about 100 tons of fuel to experience the real benefits of using diesel.
It's understandable why lightweight diesel engines are not necessarily suitable for small yachts. And if you do decide to buy a diesel engine for installation on a small yacht, keep in mind that you are paying a high price with no guarantee that you will receive any advantage. Gasoline engines are just as reliable, but significantly cheaper, more efficient and easier to maintain.
If you are interested in boat rental in any region of the world popular for yachting, we can offer our services - our company's specialists are ready to choose you the best deals on the market and provide quality support at all stages of the transaction. We wish you a successful choice and purchase of the yacht of your dreams!