Choosing a power unit for a boat is always a search for a compromise between power, weight and cost of ownership. Power 9.9 hp. It's considered the middle ground for small inflatable boats and light aluminum boats, and it's the number that allows you to operate the equipment without having to register with GIMS, which saves you time and money, but behind this magic number there are many technical nuances that you need to consider when buying.
The market is saturated with offerings from high-profile Japanese brands to low-end Chinese counterparts, and it’s not easy to understand this diversity: you have to decide on the type of engine, control system, length of lower unit and a variety of other parameters, the right choice will ensure comfortable and safe operation on the water for many seasons.
Two-stroke or four-stroke: what to choose
The first and most important question that arises before the buyer is the tactility of the engine. Two-stroke engines (2T) are traditionally lighter than their counterparts, which is critical for small PVC boats, where every kilogram on the transom affects the trim, they are easier to transport because they are not afraid of tilting in either direction, and have cheaper maintenance in the short term.
On the other hand, four-stroke (4T) are more efficient and environmentally friendly, and their fuel consumption can be 30-50% lower, and their noise and vibration levels are much lower, which is especially appreciated by fishermen who are fishing on the track or trolling. However, their weight often outweighs all the advantages: a 9.9 hp four-stroke engine can weigh 10-15 kg more than its two-stroke counterpart.
The choice often depends on the use case: If you often drag a boat on the roof of a passenger car or lower it manually from the shore, a two-stroke will be more reasonable. For long walks in large reservoirs, where fuel economy and the absence of the smell of gasoline in the cockpit are important, a four-stroke scheme is preferable.
- 🚀 2T: High specific power, low weight, the ability to transport in any position, simplicity of design.
- ⛽ 4T: Low fuel consumption, quiet operation, no need to mix oil with gasoline, long life.
- ⚖️ Weight: Two-strokes are 20-30% lighter, which is critical for boats up to 3.6 meters long.
⚠️ Warning: When choosing a two-stroke engine, be sure to consider the need to prepare a fuel mixture. Using pure gasoline will lead to cylinders being bullied and the engine will fail in a matter of minutes.
Technical specifications and impact on driving performance
The 9.9 horsepower figure only indicates the maximum power on the crankshaft, but does not reflect the actual traction specifications. torqueMotors with a larger cylinder capacity (e.g. 200cc vs 169cc) usually have better traction at low revs.
Equally important is gear ratio. For heavy boats or flat-bottomed boats (Kandak), engines with a traction gearbox with a lower gear ratio are better suited, allowing the propeller to rotate at lower speeds at the same crankshaft speed, increasing the focus and efficiency of the propeller.
You also have to look at the ignition and carburetion system. ignition (CDI or TCI) provide a stable spark at all rpms, making it easier to start and improve engine performance. Carburetors with petal valves at the intake improve cylinder fill and elasticity.
| Parameter | two-stroke motor | four-stroke engine |
|---|---|---|
| Weight (average) | 26-32 kg | 36-42 kg |
| Fuel consumption | 3.5 - 4.5 l/h | 2.0 - 2.8 l/h |
| Resource to overhaul | 1500-2000 motor-hours | 3,000 to 4,000 motor-hours |
| Transportation | In any situation | Only vertically. |
The length of the lower unit and the choice of screw
The right length of the lower unit is the key to the efficient operation of the screw and the absence of cavitation. S (Short) 381 mm, L (Long) 508 mm and X Extra Long: 635 mm. Inflatable boats are most often short legs (S) because the transom is low, and placing a long leg on a low transom will cause the motor to bury in water and lose speed.
The propeller is the second engine of your boat. The propellers are often averaged. If the boat is loaded heavily (fishermen + gear + dog), the regular propeller may not spin the engine to working speed, in which case you need to replace the propeller with a model with a smaller pitch.
The material of the screw also matters. Aluminum screws are cheap and easily recoverable when hitting rocks, just bending. Stainless steel screws are more expensive, but provide better hydrodynamics and hold shape, giving you an increase in speed of up to 3-5 km / h.
To select the screw, use the tachometer. The engine should reach the maximum recommended speeds (usually 5000-5500 rpm) with the boat fully loaded and the throttle is open.
Overview of popular brands and models
The market leaders are traditionally considered Japanese brands: Tohatsu, Yamaha, Suzuki and Honda. Tohatsu often acts as an OEM for other brands, offering the benchmark reliability of two-stroke circuits, their engines are famous for excellent traction and unpretentiousness to fuel quality.
European manufacturers, such as Mercury and YamahaThey're all about technology and comfort. FET Mercury's Fuel Efficient Technology has significantly reduced costs.Hidea, Parsun, HdX) in recent years, the quality has been significantly improved, offering copies of proven Japanese models at a price 30-40% lower than the original.
When choosing a Chinese, it is important to look at the year of production and the specific manufacturer. Many models are assembled on the same lines as the branded ones, but undergo less stringent quality control. However, for a 9.9 hp engine that does not operate 24/7, this is often an acceptable compromise.
The secret of the 9.9 rework at 15 hp
Many 9.9 hp motors are structurally 15-horsepower but are limited to software or installing a limiter in a carburetor. Removing the limiter and flashing (if possible) often allows for full power. However, this action removes the warranty and may be illegal in your jurisdiction.
Operation and maintenance in season
Long engine life is directly dependent on service quality. For two-stroke engines, it is critical to use quality oil with labeling. TC-W3Cheap oils form a garlic on candles and piston rings, leading to a drop in compression. The mixing ratio is usually 1:50 for modern motors, but older models can require 1:25.
Four-stroke engines require regular engine oil replacement, the first replacement must be made after running (usually 10 hours), then every 50-100 hours or once a season, and you also need to monitor the state of the water pump: if the trickle of the control became weaker, it may be that the cap was clogged with grass or worn out the pump itself.
Storing the engine in the off-season also requires preparation: the engine must be developed from a carburetor or canned, and lower unit greased with a special lubricant to prevent corrosion, it is better to keep the engine upright, removing the candle and putting some oil into the cylinder.
☑️ Seasonal engine maintenance
⚠️ Warning: Never keep a full tank of gasoline inside a room (garage, house) Gasoline vapors are heavier than air and can accumulate near the floor, creating an explosive situation.
Legal aspects and registration
One of the main reasons for the popularity of 9.9 hp engines is the possibility of operating without registration with GIMS (in Russia and several CIS countries), according to current legislation, a small vessel weighing up to 200 kg and engine power up to 10 hp (inclusive) does not require registration, which avoids annual taxes and inspections.
However, it is worth remembering that the restriction concerns the maximum passport power. If the engine documents indicate 9.9 hp, but when checking it turns out that it is easily converted into 15 hp and has the appropriate markings, the inspector may have questions. Buying a 9.9 hp engine is the only legal way to do this. avoid bureaucracy.
It is also important to consider the total power if the boat has more than one engine, in which case the power is added, and the ownership of the rights to operate a small vessel (GIMS license) with a power of up to 10 hp is also not required if the boat is not used for commercial purposes.
Buying a 9.9 hp engine exempts the owner from the registration of the boat, annual taxes and the need to have the rights of the GIMS, which makes this class of equipment the most popular for recreation.
FAQ: Frequently asked questions
Can I convert the 9.9 hp engine into 15 hp on my own?
Technically, this is often possible by removing the intake lobe limiter or reflashing the CDI, but this voids the warranty. In addition, operating a converted motor on an unregistered vessel is a violation of GIMS rules and can result in a fine.
Which petrol is better to fill: 92 or 95?
Most modern outboard motors, especially two-stroke ones, are designed for AI-92 gasoline. Using 95th gasoline can lead to higher temperature operation and detonation if the engine is not electronically adapted.
Do I need to run a new engine?
Yes, break-in is mandatory for both types of engines, usually 10 hours of work on an enriched mixture (for 2T) or with a speed limit (no more than 50% of the gas), which is necessary for the burning of piston rings and bearings.
Why does the engine stop at high speeds?
Most often, the cause lies in the fuel system: clogged with the carburetor jettison, contaminated fuel filter-sludge tank or impaired ventilation of the tank (creates a vacuum), and it is possible to get water into the fuel mixture.