Planning a fishing trip or a water trip always starts with the question of fuel supplies. Fuel consumption of the outboard motor It's a parameter that every boat owner cares about, because it's a huge part of the range and the cost of getting to the water, and many newcomers mistakenly rely on the manufacturer's data-sheet figures, but the actual operation makes its own adjustments to the theoretical calculations.
In practice, the appetites of the engine can differ significantly from the figures stated in the manual, due to many factors, from the quality of the fuel and the setting of the carburetor to the state of the screw and weather conditions. Understanding the mechanics of combustion of the mixture and the effect of the load on the crankshaft will allow you not only to avoid the trouble of stopping in the middle of the reservoir, but also significantly extend the life of the power plant.
In this article, we'll take a look at how consumption is generated, how it's driven, how it's used to drive, and how to calculate the amount of gasoline you need for long trips, and how to operate it properly is not just about saving money, but also about keeping you safe on the water.
Factors Affecting Gasoline Consumption
The first thing to learn is that there is no single flow figure for a particular motor model. outboard motor It works in an ever-changing environment, where every element of the system contributes to the final balance. The main factor, of course, is the load on the lower unit and the propeller. If the boat is overloaded with passengers or equipment, the engine has to work at higher revs to maintain plane, which dramatically increases the consumption of the mixture.
The second critical aspect is the technical condition of the unit: clogged jelly, the wrong angle of ignition or air suction can change the composition of the mixture, making it too rich, in which case some of the gasoline simply flies into the exhaust pipe without doing useful work. Regularly maintenance And cleaning the carburetor can return the performance to factory values.
Nor can we ignore the hydrodynamics of the body and the state of the propeller: the slide through the water should be perfect, the shelling of the bottom, the chips on the blades of the propeller or the wrong pitch of the propeller create additional resistance, the motor has to "crush" the water with greater force, expending excess calories.
⚠️ Attention: Using gasoline with an octane number below the manufacturer's recommended (for example, an AI-92 instead of an AI-95) can cause detonation, which will not only increase consumption, but also lead to burnout of the pistons and engine failure.
Driving style also plays a role: the sharp opening of the throttle valve ("gas to the floor") requires instant enrichment of the mixture, which creates peak fuel emissions. Smooth operation of the gas handle allows the engine to operate in optimal combustion mode.
Theoretical calculation and data-sheet figures
Outboard motor manufacturers typically report two-mode flow rates: idling and maximum power. However, these data are often obtained in ideal laboratory conditions that are difficult to replicate in a real body of water. The standard formula for a two-stroke engine's gross flow rate is 300-400 grams per horsepower per hour at full load. For four-stroke units, this figure is lower, at about 200-250 grams.
It's important to understand the difference between modes of operation. When idling, even a powerful engine consumes little -- usually about 0.5 to 1 liter per hour, regardless of horsepower. The main "eating" of gasoline begins when it goes into planing. This is where the main "eating" of gasoline begins. passport They can be at odds with reality by 15-20%.
Why is the real cost higher than the passport?
Factory tests are conducted on a special barge with a perfect screw, in calm and at the optimum water temperature, but in reality there is wind, wave, fouling of the screw and imperfect fuel quality, which in turn gives an increased appetite of the engine.
For accurate travel planning, it is better to use empirical data obtained by experienced water engines, or to lay a margin of 20% to the calculated value.
| Engine power (hp) | Type of engine | Consumption (l/hour) of min. | Expenditure (L/hour) max. |
|---|---|---|---|
| 5 hp | 2 bars | 1.5 | 2.2 |
| 15 hp | 2 bars | 4.5 | 6.0 |
| 30 hp | 4 bars | 5.0 | 8.5 |
| 50 hp | 4 bars | 9.0 | 14.0 |
| 90 hp | 4 bars | 18.0 | 28.0 |
Passport consumption is the ideal minimum. For real calculations, always increase factory numbers by 15-20%.
Difference between two-stroke and four-stroke motors
Choosing between two-stroke and four-stroke is often a dilemma when buying.four-strokeThey are clear leaders, with their separate lubrication system and full combustion cycle, they consume 20 to 30 percent less gasoline at the same power, and they don't require a gas oil mixture to make it easier to operate.
Two-stroke engines (two-stroke) It is simpler and lighter in design, but some of the fuel mixture is lost by being ejected through the exhaust window along with the exhaust gases. This is an inherent feature of their design. However, modern direct injection models (E-TEC, OptiMax) have learned to minimize these losses by approaching the cost-effectiveness of four-stroke analogues, while maintaining lightness and agility.
You also have to consider the cost of ownership. Even if a two-stroke eats more, it's cheaper to buy and repair. Economic efficiency It consists not only of the price of a liter of gasoline, but also of the engine life, the cost of oil and the price of the unit itself.
- 🛥️ Four-stroke engines are quieter and more environmentally friendly, which is important for fishing and protected areas.
- ⚙️ Two-stroke engines are less sensitive to boat roll and can operate in any position.
- 💰 The difference in consumption pays off only with a very large run-up (more than 100 motor hours per season).
The impact of the screw and settings on efficiency
The propeller is the very element that turns the shaft into the boat's motion. The wrong screw can negate the benefits of an economical motor. If the propeller pitch is too large for a given boat, the motor cannot spin to maximum speed (does not go into cutoff) in underweight mode, which leads to overload and overruns.
Conversely, a step that is too small will cause the engine to howl at the maximum speed, without developing sufficient thrust, in which case you pay for the speed of rotation, not for the promotion. The ideal situation is when the boat is fully loaded and the throttle is open, the engine goes to the upper limit of the recommended range of revs (WOT - Wide Open Throttle).
Besides the pitch, the diameter and number of blades are important. Three-bladed screws are usually more efficient at high speeds, whereas four-bladed ones are better at keeping the boat on plane at low revs, which is useful for trolling or towing.
⚠️ Attention: Regularly inspect the edges of the propeller blades, even small chips or burrs disrupt the flow of water, reducing efficiency by 10-15% and increasing vibration, which indirectly leads to increased fuel consumption.
The carburettor's setting is also critical: if the mixture is too rich (a lot of gasoline, not enough air), the engine will smoke and consume excess. If it is poor, there is a risk of overheating. The optimal setting can be determined by the color of the candles: it should be brick-brown. White plaque will indicate a poor mixture, black loam will indicate a rich one.
Do a full tank test: run a known cruising speed distance (about 3,500-4000 rpm) and measure the remainder, which will give the most accurate flow figure for your particular boat-motor-propeller bundle.
Driving style and operating conditions
The way you drive a boat directly affects your wallet. Aggressive style with constant acceleration and braking prevents the engine from entering economical mode. For two-stroke engines, the most economical mode is often not top speed, but confident planing at 70-80% of power.
The environment also dictates its rules: headwind and high wave increase the resistance of the water, the boat starts to prowl, hit the wave, and the motor has to constantly throw power to hold its course. fuel It can grow one and a half times compared to the calm.
Water and air temperature matter, too. Cold water has higher density, which increases resistance. In summer, in hot weather, air density drops, the mixture gets richer (if there is no automatic correction), which can also have a slight effect on the efficiency of combustion.
It's important to distribute the load properly in the boat. Shifting the center of gravity to the nose will cause the boat to peck, increasing the area of the wetted surface. Shifting on the stern can lead to yaw. Uniform loading ensures the optimal position of the lower unit relative to the water horizon.
Practical advice on fuel economy
You can save on fuel not only by choosing a motor, but also by following simple rules of operation. First of all, check the condition of the lower unit. If there are algae or shells on the anti-cavitation stove or propeller, be sure to remove them. A smooth surface improves flow.
Use only quality fuel with appropriate additives. Old gasoline, which has been in the canister for six months, loses its properties and burns less efficiently. Adding fuel stabilizers during long-term storage of the boat will help avoid problems with the carburetor.
☑️ Checklist of economical operation
Don't forget the tilt of the lower unit (trim). A properly set angle allows the boat to go out faster and reduces water resistance. If the boat's nose is too upside down, you swim "on the belly", if you go too down, "dig water".
Plan your route with current and wind in mind. Going with the current or wind is always more economical than fighting the elements. If possible, choose the route to return against the current when the boat is lighter (less fuel is drunk, the fish caught has not added weight, although this is minimal).
Frequently Asked Questions (FAQ)
How many liters of gasoline should I take for fishing for 8 hours?
To calculate, multiply your engine's hourly consumption by 8 and add 30 percent of the margin. For example, a 15 hp engine eats about 5 l/h. 5 * 8 = 40 liters. Plus a 12 liter margin. Totally, you need to take about 50-55 liters. It's always better to have a margin than to stand a kilometer from the base.
Does the new engine actually consume more?
Yes, during the break-in period (the first 10 hours), the engine runs on an enriched mixture, and the flow rate can be higher than nominal, and the rubbing parts have not yet been worn, which creates additional resistance, after running, the indicators stabilize.
Does the use of oil for two-stroke motors affect the flow rate?
Quality synthetic oil burns cleaner and allows you to adjust the carburetor more accurately. Cheap mineral oil can coke candles and exhaust windows, disrupting the engine and increasing fuel consumption. Quality lubrication indirectly saves gasoline.
How to find out the actual cost if there is no on-board computer?
The most reliable method is the full tank method. Pour the tank up to the neck, travel a known distance (for example, 20 km) at constant speeds, then add it back to the neck from the measuring tank. The amount of fuel consumed is your consumption for this distance.