The question of how fast a 9.9 horsepower outboard boat can develop is one of the most debated among beginners, a power threshold often considered the “middle ground” for small inflatable and aluminum vessels, as it does not formally require registration with the GIMS (subject to length and weight conditions) and does not require the rights to operate a small vessel in many cases.
Much depends on what we mean by the term “speed.” Maximum speed on perfectly smooth water with minimal loading is one thing, and cruise-speedIt's a completely different story, where the boat is confidently planing with two passengers and equipment. In this article, we'll go through the physical limitations, the effect of gear ratio and the correctness of the screw selection so that you can get the most out of your own gear. Tohatsu, Yamaha or Hidea.
It is important to note right away that 9.9 hp engines are technically often “strangled” versions of 15-horsepower units, but this does not always guarantee identical acceleration dynamics due to differences in the settings of the carburetor and exhaust system. The actual planing speed for most PVC boats with a length of 3.2-3.6 meters with a 9.9 hp engine starts from 22 km / h and rarely exceeds 28 km / h at full load. Further increase in indicators is possible only due to changes in hydrodynamics or weight.
Factors affecting the performance of the vessel
Before we get to the numbers, we need to understand which variables are involved in the speed equation. An engine is just a source of energy, but how that energy is converted into motion depends on a variety of parameters. case-typeinflatable floor boats (BBBs) have greater water resistance due to underfloor deflection under weight than hard floorboard boats or aluminum boats.
The second critical parameter is weight-weight A 9.9 hp engine is extremely sensitive to overload, and if you plan to take two people on board, a fuel tank, an anchor and a sonar, weight gain can reduce top speed by 20 to 25 percent. transomIf the engine is installed too deep or too high, the efficiency of the propeller falls, which directly affects the final result.
⚠️ Attention: Installing an overtilt motor (different) can lead to cavitation of the propeller and loss of traction, even if the engine speed is maximum.
The third factor is wind and turbulenceFor a low-power engine, a headwind of even 3-4 points becomes a serious obstacle. The boat stops glides and goes into displacement mode, where the speed rarely exceeds 6-8 km / h, regardless of the engine power, so all the figures stated by the manufacturer are relevant only for calm weather.
The impact of the propeller on the dynamics of acceleration
The propeller is the "transmission" of an outboard motor, and its correct selection can change the speed of the boat by 3-5 km / h. Standard screws, complete with 9.9 hp engines, usually have a pitch in the range of 8-9 inches. They are designed for medium load and versatile use. However, if your goal is maximum speed on a lightweight boat, it makes sense to consider screws with a large pitch, for example, 10 or 11 inches.
As the propeller pitch increases, the boat travels a longer distance in one turn, which theoretically increases speed, but there is a danger: the engine may not have enough power to spin such a propeller to its working speed (usually 5000-5500 rpm). If the engine does not go to the power shelf, it runs in overload mode, which leads to overheating and increased fuel consumption. Optimal screw This allows the engine to reach maximum speed when the boat is fully loaded.
The material of the screw also plays a role: Aluminum screws are cheaper, but they are more flexible and can deform when impacted, changing the geometry of the blades. Stainless steel It's more expensive, but it keeps the pitch perfectly, and it has thinner blades, which reduces water resistance, and for speed, a steel screw will always be more efficient, even with the same engine power.
- 🚀 8-9 inch propeller pitch: Optimal for heavy boats and full load, provides better acceleration but less maximum speed.
- ⚓ 10–11 inch propeller pitch: suitable for light boats with 1-2 passengers, allowing you to reach maximum speed on a straight line.
- 🛡️ Material: Steel gives an increase in speed up to 1-2 km / h compared to aluminum due to better hydrodynamics of the blades.
Before buying an expensive steel screw, try experimenting with the installation angle of the lower unit – sometimes changing the inclination of the motor by one division gives a greater effect than replacing the screw.
It is also worth mentioning the so-called "speed" propellers with modified blade geometry. They can cost 3-4 times more than regular ones, but on a 9.9 hp engine, their installation is often economically impractical. The speed gain will be minimal (about 1 km / h), which can be lost due to headwinds. For this power, it is more important to monitor the condition of the anti-cavitation plate and no damage to the blades.
Speed comparison on PVC and aluminum boats
The type of hull material dictates its laws of physics. PVC boats, especially those with inflatable tubes, have a softer stroke but also greater drag. When you get on plane, the bow of the boat picks up, and the area of contact with water decreases. A 9.9 hp engine on a PVC boat with a length of 3.0-3.2 meters is able to accelerate it to 20-24 km / h with one person. If the length increases to 3.6 meters, the speed drops to 18-22 km / h, as the area of the wetted surface increases.
Aluminum boats ("Kazanki", "Crimea", "obob") have a hard bottom and sharp entrance into the water, which favorably affects the speed specifications. At the same power of 9.9 hp, light aluminum with a length of 3.5-4.0 meters can reach speeds up to 28-32 km / h. The key factor here is the weight of the boat itself: modern aluminum models weigh much less than Soviet counterparts, which allows them to more easily go to gleaming.
| Type of boat | Length (m) | Loading (kg) | Average speed (km/h) | Mode of traffic |
|---|---|---|---|---|
| PVC (NDD) | 3.2 | 150 (1 man + motor) | 24-26 | planing |
| PVC (Pyol) | 3.6 | 220 (2 persons + cargo) | 20-22 | planing (tension) |
| aluminum | 3.8 | 200 (2 persons + cargo) | 26-29 | Confident glossing |
| Aluminum (old) | 4.0 | 250 (2 persons + cargo) | 12-15 | Transitional/Displacement |
Special attention should be paid bottom-geometryThe flat bottom of aluminium boats such as "Crimea" or "Kazanka-M" with low engine power can give a strong impact load on the hull and passengers, but provides good speed. PVC-silver boats softer wave, but require more energy to accelerate. For the engine 9.9 hp, the ideal compromise is light aluminum boats with simple geometry or inflatable boats with a hard bottom (RIB) of small size.
Fuel consumption and efficiency at different speeds
Speed is directly correlated with engine appetite. A 9.9 hp engine in two-stroke uses a mixture of gasoline and oil, and a four-stroke engine uses pure gasoline. At full gas (WOT - Wide Open Throttle), a two-stroke can eat between 3.5 and 4.5 liters per hour. However, few people drive constantly at the maximum. Cruising speedThe most economical mode, which is about 70-80% of the maximum, is the most economical mode.
When driving in planing mode, but not at full speed (about 4000-4500 rpm), the consumption of a two-stroke engine decreases to 2.5-3 liters per hour. Yamaha F9.9 or Tohatsu M9.9BThe difference seems small, but on long transitions, the four-stroke will give tangible fuel economy and no need to mix oil.
It is important to understand that trying to go at a speed close to maximum, constantly, not only increases the consumption, but also reduces the life of the engine. Piston group It's the best way to go fishing or cruising is to keep the boat sliding with confidence, but the engine is running at 80 percent of its capacity, and that balances travel time and range.
⚠️ Warning: Prolonged operation of a 9.9 hp two-stroke engine at full speeds without sufficient cooling (for example, when driving against the current at low speed) can lead to overheating and bullying.
The problem of access to glossing and its solution
The most common problem with 9.9 hp motor owners is that they can't get a loaded boat to plane, the boat is prowling, the nose is picking up, but the plane of slip is not achieved, in this mode, the speed is low (10-12 km / h), fuel consumption is high, and control is difficult, the main reason is insufficient traction to overcome the hump of water resistance.
There are a number of techniques that can be used to solve this problem. hangingPassengers and cargo must be shifted closer to the transom to unload the bow of the boat. Second, using transom wheels or hydrodynamic wings. Wings mounted on the engine's lower unit create downforce on the transom, lowering the boat's nose and helping to get into plane mode faster.
☑️ Checking the reasons for the lack of glossing
It is also worth checking the technical condition of the engine. carburetor If you're not set up correctly (a mixture that's too poor), you're not going to get full power, and if you're dirty, you can also smother the engine, and you're not going to get to the speed you want to plane, and you're going to have regular maintenance, which is more important than more powerful engines, because you're going to have a 9.9 hp power reserve.
Comparison of two-stroke and four-stroke engines 9.9 hp
The choice between 2T and 4T in the 9.9 hp class is particularly acute. Two-stroke (2T) motors are lighter than their four-stroke counterparts (4T) by about 30-40%. For an inflatable boat, where every kilogram counts, this is a significant argument. 2T motor It is faster gaining momentum, it is more "sharp", which helps to tear the boat into planing easier.
Four-stroke engines are heavier, but they provide more stable traction at low rpm, which is important for trolling. They are quieter, more economical and more environmentally friendly. However, because of the weight of the 4T, the engine may not allow a lightweight PVC boat to plane with two passengers where the 2T engine can easily cope. Tohatsu M9.9B (4T) weighs about 27 kg, while its two-stroke counterpart is about 21 kg.
Can I increase the engine power of 9.9 to 15 hp?
Technically, many 9.9 hp engines (especially the Tohatsu/Nissan and Hidea) are copies of 15-horsepower models. Increased power is possible by replacing the restrictive washer in the carburetor or reflashing the ECU (on models with an injector). However, this cancels the warranty, increases fuel consumption and may require a higher speed rotor.
When choosing between engine types, you need to start from the type of boat. For a light PVC boat up to 3.3 meters, a two-stroke boat is better because of the weight. For a heavier boat with a hard bottom or aluminum, where comfort and economy are important, a 9.9 hp four-stroke will be preferable, even taking into account the loss of a couple of kilometers of speed.
Legal aspects and limitations of GIMS
The popularity of 9.9 hp engines is largely due to the law, and according to the registration rules for small craft, boats weighing up to 200 kg and engine power up to 10 hp (inclusive) are not subject to registration with the GIMS unless they are used for commercial purposes, which allows owners to avoid annual inspections, taxes and the need to have boatmaster rights.
But there's a subtle point here: 9.9 hp is often a marketing ploy. Technically, the motor can produce more, but the documents say 9.9. boat registration certificate If you have a 9.9 hp engine, and the boat is light, you won't have any problems, but if you sell out a 15-strong engine, you're breaking the law.
Also, you need to keep in mind the categories of rights. You don't need a license to drive a boat with a 10 hp engine. But if the power exceeds this threshold (even by 0.1 hp formally), you need a certificate of license to drive a small craft of the category "M." So buying a 9.9 hp engine is often a conscious choice in favor of freedom from bureaucracy, even at the expense of speed.
The 9.9 hp engine is a compromise: you sacrifice high speed and dynamics for the legality of swimming without registration and rights, as well as savings on fuel and maintenance.
Is it true that the engine 9.9 hp does not keep the plane on the wave?
It depends on the height of the wave and the weight of the boat. At a wave height of 0.3-0.5 meters, a boat with a 9.9 hp engine will constantly "fall" from plane to displacement mode, since the power reserve is small to overcome the increased resistance. For a confident ride on the wave, it is desirable to have a power reserve of at least 15-20%.
Which one is better for fishing with a 9.9 engine?
For fishing, where it is not the maximum speed, but the thrust and ability to move at low speeds (trolling), it is better to leave a regular propeller with 8-9 inches increments. It will provide the best acceleration with a full boat of gear and allow the engine to work stably at low speeds without stalling.
Should I buy a used 9.9 hp engine for the first boat?
Yes, it's a great option. 9.9 hp engines are very reliable and easy to repair. Even a used Japanese or high-quality Chinese engine will last a long time. The main thing is to check the compression (for 2T) and no extraneous noise when buying it, which will save the budget for buying a better boat or sonar.