Planning a fishing trip or a water trip always starts with the question of fuel supplies. Gasoline consumption of outboard motors It's a variable that depends on a variety of factors, from engine power and boat weight to propeller condition and weather conditions. Many watercraft owners are often surprised to find that the actual numbers at the gas station differ significantly from the advertised booklets of manufacturers.
In this article, we will discuss how your appetite is formed. outboardWe'll give you average tables for popular models, and we'll learn how to correctly calculate the fuel supply for long trips, and understanding these processes will help you avoid unpleasant situations in the middle of a reservoir and optimize the budget for the operation of equipment.
It's worth noting that even the same power engines of different brands can show different efficiency, which is influenced by the combustion technology of the mixture, the quality of the carburetor or system. injectorAnd we're going to look at what's going on with the numbers in the gas station check.
Factors Affecting Fuel Consumption
The first thing to consider when calculating is the engine mode. Full gas. It causes the motor to consume the maximum amount of mixture, while at idle speeds the flow rate is minimal. However, the most economical mode is often to move 70-80% of the maximum power when the engine has already entered the operating temperature mode, but has not yet been forced to the limit.
The second critical factor is the hydro-aerodynamics of your boat, whether it's dirty bottom, algae fouling, or mismatched. propeller They can increase fuel consumption by 15-20%, and the weight of the boat and the number of passengers are directly correlated with the amount of gasoline burned: the heavier the load, the more energy it takes to move it in the water.
The technical condition of the engine is not the last: contaminated jelly carburetor, improper setting of the angle of advance of ignition or worn candles can disrupt the mixing process, as a result, the mixture becomes either too rich (bad burn, scorching, overspending) or too poor (overheating, risk of piston burn).
To fine-tune the carburetor, use a gas analyzer or twist candles after working in different modes: the color of the electrode should be brick-brown, not white or black.
Theoretical calculation: formulas and norms
There is a simplified engineering formula that allows you to estimate the maximum expenditure It is estimated that for every 10 horsepower of power, approximately 1 liter of fuel mixture per hour is required when driving at full gas. WOT (Wide Open Throttle).
To plan the fuel supply for the route more accurately, you need to consider cruising speed. In practice, the motor rarely runs at 100% power. Usually the movement takes place at speeds of about 60-70% of the maximum. fuel-use It is much lower, and one refueling can be enough for a much longer distance.
It's important to distinguish between litres per hour and 100 kilometers per journey. The speed of a boat is very dependent on wave, wind and load, so if you know the hourly flow, you can estimate the autonomy time, but not necessarily the exact distance.
Comparative fuel consumption table
Here are the averaged data from tests of different engine models, which will help you to get a first idea of how many liters of gasoline you need for your car. boat-engine depending on its power.
Note that the data are relevant for a high-quality fuel mixture (for 2T) or pure AI-92/95 gasoline (for 4T) using the recommended oil. The use of low-octane fuel may require correction of the ignition angle, which also affects the economy.
| Power (hp) | Type of engine | Max. flow (L/h) | Cruising consumption (L/h) | Model model |
|---|---|---|---|---|
| 5 hp | two-stroke | 1.8 - 2.2 | 1.0 - 1.2 | Tohatsu M5BDS |
| 9.9 hp | two-stroke | 3.5 - 4.0 | 2.0 - 2.5 | Yamaha 9.9 GMHS |
| 15 hp | four-stroke | 4.5 - 5.0 | 2.5 - 3.0 | Suzuki DF15A |
| 30 hp | four-stroke | 8.0 - 9.0 | 4.5 - 5.5 | Mercury F30 |
| 60 hp | four-stroke | 18.0 - 20.0 | 10.0 - 12.0 | Yamaha F60 |
As you can see from the table, higher-power four-stroke engines show better performance at partial loads than two-stroke counterparts of the same power, but at low power, the difference may be less noticeable or even absent due to the weight of the engine.
☑️ Pre-measurement check
Two-stroke vs. four-stroke: who is more economical?
The eternal debate of boat owners: what's the best thing to do in operation? four-stroke motors It's 20 to 30 percent more economical, thanks to a better cycle and no fuel loss through the exhaust window, but the real picture depends on the operating conditions.
Two-stroke engines, especially modern multi-stage purge models, can be surprisingly efficient at high revs. They have the advantage of being high power and lighter. If your boat is lightweight (PVC), a 9.9 hp two-stroke can be more economical than a heavy four-stroke of the same power, since it does not need to carry the extra weight of the engine itself.
On the other hand, four-strokes are better at trolling and low-speed driving, and they don't require oil mixing, which eliminates the human factor and the risk of running on pure gasoline, leading to bullies.
⚠️ Attention: Never use pure gasoline in a two-stroke engine without adding oil, which will cause instant jamming of the piston group and costly repairs, and the mixing ratio is usually 1:25 or 1:50, depending on the manufacturer's instructions.
Secrets of saving on two-tacters
Use only fresh mixtures (not older than 2 weeks), as the oil tends to delaminate and precipitate, which disrupts lubrication and worsens combustion. It is also recommended to use synthetic oils for 2T engines, which burn almost without a residue, preventing exhaust windows from coking.
Effect of propeller on flow
The propeller is the transformer of engine power into thrust. The wrong pitch of the propeller can negate the efficiency of the most perfect engine. If the propeller is too big a step for the boat, the engine will not be able to spin to working speed, will run in overload mode and consume a lot of fuel without developing speed.
Conversely, a small-step propeller will allow the engine to rotate easily, but the boat will not go faster, and the consumption per kilometer of the journey may even increase due to the fact that the engine will operate at high speeds at low speed. The optimal is the selection of a propeller, in which at full gas with full load the engine goes to the upper limit of the recommended range of revolutions (for example, 5000-5500 rpm).
And you also have to consider the condition of the blades, because chipping, bullying, or deformation disrupts the flow flow, creating cavitation and vibration, and not only does this reduce efficiency, but it can also cause the gearbox to collapse.
Replacing a standard propeller with a model with optimal pitch can reduce fuel consumption by up to 10-15% and increase the boat's top speed.
Practical advice on reducing costs
There are a number of ways to reduce your appetite. outboard First, keep the bottom clean, and the bottom of the boat is covered with seashells or algae, and the bottom creates a lot of water resistance, making the engine work harder.
Second, distribute the load correctly. The bow of the boat should not be too raised or, conversely, buried in water. Optimal differentiation is achieved experimentally and by moving passengers or luggage. The use of transom plates (for hull boats) also helps to set the correct angle of attack.
- 🌊 Clean the lower unit and screw from algae and debris regularly to reduce water resistance.
- ⚙️ Watch the state of the thermostat: work on an underheated engine increases the consumption of the mixture.
- 🛢️ Use quality fuels and oils that meet specifications
JASO FD2T orFC-W4T.
Remember, saving should be sensible: Trying to save a penny on oil or candles can lead to a major overhaul, the cost of which will cover all the savings on gasoline in a few seasons.
⚠️ Attention: Long-term idling (e.g., waiting for fish) on two-stroke engines can lead to candles being fouled with soot and loss of power. Periodically give the motor neutral gas to clean the combustion chamber.
How to convert HP to kW for calculation?
To convert horsepower into kilowatts (often required for technical calculations), use a coefficient of 0.7355. Power (kW) = Power (hp) * 0.7355However, it is more convenient to operate with horsepower to calculate fuel consumption in liters.
Does the octane number affect the flow?
Yes, it does. Using gasoline with an octane number below the recommended (for example, an AI-80 instead of an AI-92) leads to detonation. The electronics (or mechanics) of the engine tries to adjust the angle of ignition, which leads to incomplete combustion and increased consumption. Putting 98th gasoline into an engine designed for the 92nd will not save, but only increase costs.
Is it true that the 4-tact is always quieter?
In most cases, yes, four-stroke engines are quieter and softer due to the separate intake and exhaust strokes. E-TEC or OptiMax They can also be very quiet, especially at low rpm, although at high their characteristic sound is still different.