Choosing a power unit for a small vessel is always a compromise between weight, cost of ownership and desired speed. 9.9-20 horsepower It is considered the middle ground for owners of inflatable boats and small boats, as it allows you to develop a slinging course without the need to obtain a license to operate a small vessel in a number of jurisdictions, although the legislation is constantly changing and requires verification.
For many aquatic motorists, switching from 9.9 hp to 15 or 20 hp becomes a logical step when standard power is no longer enough to go to the plane with full load, including the passenger, equipment and fuel. Two-stroke engines In this niche, traditionally valued for lightness and quickness, while four-stroke They're winning the market because they're quiet and cost-effective, and understanding the technical details of each type of engine will help you make the right choice that will last for years.
In this article, we will discuss in detail the design features, real fuel consumption and practical aspects of operating engines with a capacity of up to 20 hp You will learn why some models 9.9 hp are technically "strangled" versions of 15-horsepower units, and whether to pay for the possibility of software or mechanical power unlocking.
Two-stroke or four-stroke: the battle of technology in the 20 hp class
The eternal dispute between the adherents of two bars and four bars in the segment 9.9-20 hp has its own unique features, different from the more powerful categories. Two-stroke engines (2Ts) are traditionally 30-40% lighter than their four-stroke counterparts, which is critical for carrying a motor by one person or putting a light inflatable boat on the transom, but they require a fuel mix to be prepared, which adds extra effort before each trip.
On the other hand, four-stroke (4T) are much quieter and more stable at idle speeds, which is highly valued when trolling or waiting for a cool fish. Not having to mix gasoline with oil makes operation easier, and the piston group resource is usually higher due to a full-fledged lubrication system. But these benefits have to be paid for by increased weight: if a two-stroke weighs about 35-40 kg, then a four-stroke can reach 50-55 kg.
⚠️ Warning: When choosing a four-stroke engine with a capacity of 15-20 hp, be sure to consider the load capacity of your boat. Excess weight of 15-20 kg on the transom can significantly reduce the payload and impair the running performance of the vessel in quiet operation.
From the point of view of acceleration dynamics, modern two-stroke models with a direct fuel injection system (E-TEC, OptiMax) are almost equal to four-strokes in terms of efficiency and environmental friendliness, maintaining the advantage in specific power. Low-speed traction Four-strokes are better, which is important for heavy boats, whereas two-strokes like high speeds, and the choice should be based on whether you plan to use the boat for quick delivery to the fishing point or for a measured rest.
The phenomenon of “9.9 hp”: hidden potential and ways to unlock power
Many experienced boaters know the secret: the engine with the nameplate 9.9 hp is often technically identical to the model at 15 or even 20 hp Manufacturers artificially limit power through the software of the control unit or the installation of a limiter in the carburetor (petal) to get into a category that does not require registration or rights. This allows buyers to purchase a more powerful unit at the price of a weaker, knowing that if necessary it can be “stirred up”.
The procedure for increasing power, often referred to as "striking", varies by brand. carburetor Or remove the plastic plug from the throttle. More sophisticated models require flashing. ECU (electronic control unit)For example, popular Tohatsu and Mercury models often have a single piston group for the ranges of 9.9-15-18 hp, differing only in settings.
- 🔧 Mechanical method: replacement of the petal in the carburetor or adjustment of the gas cable, allowing the throttle to open completely.
- 💻 Programmatic method: connecting a diagnostic computer and changing injection cards and speed limits (relevant for EFI motors).
- ⚙️ Replacement of components: In rare cases, the exhaust system or intake manifold is required to replace the increased volume of gases.
However, it is worth remembering that interference with the design of the engine can lead to loss of power. guaranteeAlso, the 9.9-horsepower version is not always identical to the older brother: sometimes the rods, pistons or cooling system differ, so before buying an engine with an eye on future tuning, you need to study the technical documentation and reviews for a specific model of the year of release.
Risks of self-increasing power
If the mixture is not properly adjusted (depletion), the piston or bully in the cylinder can burn out, and the thermal load on the cooling system increases, which in the base version of 9.9 hp could be designed for lower temperatures.
Comparative table of specifications of popular models
To facilitate the choice, we have prepared a comparison of the technical parameters of common models in the class 15-20 hp The data are averaged and may vary slightly depending on the year of release and the specific modification (long or short leg).
| Model | Type of engine | Work volume (cm) | Weight (kg) | Recommended boat (m) |
|---|---|---|---|---|
| Tohatsu MFS 20 E | four-stroke | 351 | 49.0 | 3.2 - 4.2 |
| Yamaha 15 FMHS | two-stroke | 246 | 39.0 | 3.0 - 3.8 |
| Honda BF 20 DK3 | four-stroke | 351 | 52.5 | 3.5 - 4.5 |
| Suzuki DF 20 AS | four-stroke | 351 | 56.0 | 3.5 - 4.5 |
As you can see from the table, four-stroke Honda and Suzuki have the most weight, which is their main drawback for mobile complexes. Yamaha in two-stroke version wins in weight, but loses in fuel consumption and noise level. Tohatsu demonstrates excellent weight figures for a four-stroke, making it a popular choice for PVC boats.
When choosing, also pay attention to gear ratio. For heavy boats and large propellers, it is more important. torqueIf you want to get the maximum speed on a light boat, then the engine turns over.
Fuel consumption and operation: economic aspect
Economy is one of the main arguments for four-stroke engines, in trolling or half-power mode. four-stroke It consumes 30-50% less fuel than a two-stroke engine, which is because in a two-stroke engine, a portion of the fuel mixture simply flies into the exhaust pipe without burning.
For a 15-20 hp engine, the average flow rate at full gas is approximately:
- ⛽ Two-stroke: 5-7 liters per hour.
- ⛽ Four-stroke: 3.5-5 liters per hour.
- 🐢 Trolling (both types): 0.8-1.5 litres per hour.
However, the cost of service should be considered. Two-stroke engines The four-strokes require a constant supply of oil for the mixture, which increases the cost of each liter of burned fuel by about 15-20%. Four-strokes require a change in engine oil in the crankcase (usually every 50-100 motor hours or once a season), but operate on pure gasoline.
Use fuel additives to stabilize gasoline if the engine is stored for more than a month without work, especially in carburetor models where fuel can oxidize and clog the jelly.
Rotor selection: how to unlock the potential of the engine 9.9-20 hp
Even the most powerful engine will not show its capabilities without a properly selected propeller. Factory screws are often compromised and do not take into account the specific load of the boat. If the engine does not reach the maximum recommended speeds (usually 5000-6000 rpm for 2T and 5500-6500 for 4T), then the screw is too heavy (big step).
For PVC boats with a length of 3.2-3.6 meters with a 15-20 hp engine, the best solution is often a screw with a reduced diameter or a modified pitch. Aluminum screws are lighter and cheaper, they work better on overgrown reservoirs, since when hitting a solid obstacle, the blades bend rather than break the gearbox. Stainless steel It gives you a speed increase of 5-10%, but it is more expensive and heavier.
⚠️ Warning: Never operate a motor with damaged propeller blades. The imbalance leads to vibrations that destroy the diewood and osteoils, which can lead to water getting into the gearbox and expensive repairs.
The rotor selection is an empirical process. It is ideal to have two propellers in reserve: one for single or double loading (big step), and the second for full loading of family and equipment (smaller step), you need to measure the speed with a tachometer, because it is difficult to determine the output to maximum power by hearing.
☑️ Screening of rotor status
Maintenance and extension of engine life
The life of a modern outboard motor, when properly maintained, is between 1,000 and 3,000 hours. fuel-mix For two-stroke motors, use only quality synthetic oils with labels. TC-W3The manufacturer's recommended proportion (usually 1:50 for modern motors)
Four-stroke engines require regular oil changes in the gearbox (every 100 hours) and in the crankcase of the engine. thermostat Overheating is the main enemy of any motor, and if you notice a decrease in the water pressure from the control hole, stop operating immediately and check the cooling system.
When canned for the winter, be sure to drain fuel from the carburetor float chamber (for 2T) or use stabilizers, as well as blow out the cooling system with compressed air or antifreeze to avoid freezing of water residues and cracking the block.
Regular replacement of the water pump (every 2-3 seasons) is inexpensive, but saves the engine from fatal overheating, which can cost 70% of the cost of a new engine.
Frequently Asked Questions (FAQ)
Can I register a 20 hp engine without a license if it is 9.9?
According to the legislation of the Russian Federation, registration and rights are required if the engine power exceeds 10 hp (8 kW) OR the weight of a equipped vessel with an engine of more than 200 kg. If the documents (PTS) indicate a power of 9.9 hp, then formally the rights are not necessary, even if you "suffocated". However, the GIMS inspector can take measurements, and if the actual power exceeds the norm, you will be fined and the engine is withdrawn. It all depends on how the engine is registered in the GTD and PTS.
Which gasoline is better to pour into the engine 15-20 hp?
Most modern engines (especially 4T and 2T direct injection) are designed for gasoline. AI-95The use of the AI-92 is only possible if it is expressly authorized by the instructions for your model (often for older 2T engines), pouring low-octane fuel into an engine requiring a 95th leads to detonation and burnout of the piston. Always use fresh gasoline, not older than 1-2 months.
Why does the engine stop at idle speed?
The most common causes: a contaminated carburetor (idle jicler), improper adjustment of the screw quality of the mixture, air sucking through gaskets or crankshaft ointment. It is also worth checking the spark plug - soak or improper gap can cause unstable work at low speeds.
Should you buy a Chinese engine 18-20 hp instead of used Yamaha / Tohatsu?
Chinese engines (Parsun, Hidea, Sea-Pro, etc.) are often copies of old Yamaha models. They are cheaper and guaranteed. However, the quality of casting and metal they may be inferior to the original. For heavy operation (every day) better than the original. For 10-20 trips per season, "Chinese" is a reasonable economy option, especially given the availability of spare parts.