Choosing a power unit for an inflatable vessel with a length of 320 centimeters is one of the most important decisions for the owner, since it depends on this safety, comfort and speed of movement on the water. PVC boat 320 It is a versatile size that allows two and sometimes three adults to comfortably accommodate, but its load capacity and bottom rigidity impose certain limits on the power of the engine being installed. An error in calculations can lead not only to discomfort during swimming, but also to serious problems with stability or even damage to the transom.
There are a huge number of models from various manufacturers on the market today, and it can be difficult for a beginner to navigate technical specifications such as working volume, number of cycles and engine weight. Many factors must be considered: from the type of reservoir and the expected load to the budget for purchase and subsequent maintenance. Properly selected engine power This will allow the boat to go on planing, which significantly saves fuel and travel time, while a too weak engine will only create the appearance of movement, wasting resources.
In this article, we will examine in detail all the nuances of choice, analyze the advantages and disadvantages of different types of engines, and consider specific models that have proven themselves from the best side, you will learn why the weight of the engine plays a critical role for boats of this size and how to avoid fatal errors in the configuration of your boat.
Optimum engine power for a boat 320 cm
The first and most important parameter to look at is the maximum power allowed by the boat manufacturer. For most models with a 320 cm inflatable floor (NDB) or hard floorboard, this figure varies from 5 to 10 horsepower. strictly forbiddenThis can cause the transom plate to collapse under the influence of vibration and water pressure.
5 hp motors are considered minimally comfortable for single-driver planing. If you plan to bring a passenger or a significant amount of equipment, then 5 forces may not be enough, and the boat will go in displacement mode, creating a large wave and consuming a lot of fuel. In this case, it is better to look at models at 8 or 9.8 hp, which will provide a confident getting on plane even with a double load.
There is also the concept of “hidden power”, when the engine formally has 9.8 hp, but can be reprogrammed or mechanically modified to 15 hp However, for a boat 320 cm such experiments are dangerous. hull It is simply not designed for such speeds and shock loads, which is fraught with loss of control on the wave.
⚠️ Warning: Never exceed the maximum power indicated on the boat cylinder marking table. Exceeding the limit leads to cancellation of the warranty and poses a real threat to life.
When choosing it is also worth considering that a more powerful engine is usually heavier, which for a small inflatable boat is a significant disadvantage during transportation and installation.
Two-stroke or four-stroke: what to choose
The choice between a two-stroke (2T) and a four-stroke (4T) engine is a matter for every customer. For 320 cm PVC boats, where every kilogram of weight matters, two-stroke engines are traditionally in high demand. They are significantly lighter than their four-stroke counterparts of the same power, making it easier to install the engine on a transom and carry it to the water.
Four-stroke engines are quieter, idle, and, importantly, economical. They don't require a fuel mix because they have separate oil and gas. However, they often weigh more than 20-25 kg, which can be critical for a 320 cm boat: the stern will be heavily buried in the water, especially when driving against a wave or with a passenger.
Two-stroke engines require a mixture of gasoline and special oil in a ratio usually of 1:50 or 1:25 depending on the model. They are noisier and vibrate, but provide better acceleration dynamics. For short distances and fishing, where mobility is important, 2T is often preferred.
- 🚤 Weight: Two-strokes are lighter by 30-40%, which is critical for boats 320 cm.
- ⛽ Fuel consumption: Four-strokes are more economical by 20-30% and more environmentally friendly.
- 🔧 Maintenance: 4T requires oil change in the crankcase, 2T - only mixtures in the tank.
- 📉 Price: Two-stroke engines are generally cheaper to buy and repair.
If you plan long transitions or trolling (fishing at slow speed), the four-stroke engine will be more comfortable due to the lack of need to keep your hand on the gas at idle speeds.
Motor weight: critical parameter for a small boat
For a PVC boat 320 cm long, the weight of the engine is one of the determining factors of comfort and safety. Overloading the stern causes the boat to lose driving performance, become roller and react less to steering. The optimal weight for this size is considered to be a range of 19 to 24 kilograms.
If the motor weighs more than 26 kg, the center of gravity shifts back, and the boat's nose jacks up even in standing water, which causes a "dolphining" effect when driving, which tires the driver and passengers, and also increases fuel consumption. In an emergency, overloaded stern is more difficult to control.
Modern manufacturers are looking to reduce the weight of engines by using composite materials and aluminum alloys. When choosing a model, be sure to pay attention to the "dry weight" column in the specifications. The difference of 3-4 kg can be decisive when you have to manually drag the engine on the beach or lift it to a high side.
When buying a motor, immediately purchase transom wheels. For a boat with a 320 cm engine installed, this is not a luxury, but a necessity that will save your back.
It’s also worth remembering that full weight includes not only the engine itself, but also the lower unit, and sometimes the starter or control knob if they’re not integrated into the baseline.
Comparison of popular motor models
There are many brands on the market, from the big Japanese giants to the low-cost Chinese manufacturers. To make it easier to choose, we have compiled a comparison table of popular models suitable for boats with a length of 320 cm.
| Model | Power (hp) | Weight (kg) | Type | Features |
|---|---|---|---|---|
| Tohatsu M9.8B S | 9.8 | 25.5 | 2T | Reliability, easy launch |
| Yamaha 9.9 GMHS | 9.9 | 26.0 | 2T | High traction, long resource. |
| HDX T 9.8 FTS | 9.8 | 26.0 | 2T | Budget option, availability of spare parts |
| Tohatsu MFS 9.9C S | 9.9 | 36.0 | 4T | Silence, economy, heavy |
| Mercury ME 5M | 5.0 | 19.0 | 2T | The easiest one for one. |
Japanese brands such as Tohatsu and Yamaha, traditionally leading in terms of build quality and engine life. HDX or ParsunThey often copy the design of Japanese engines, offering a lower price, but can yield as materials and anticorrosion protection.
When buying a budget model, it is important to check the availability of service centers in your area. Parts availability This is a guarantee that your season will not end in the workshop due to a missing pad or carburetor.
For a boat 320 cm "golden mean" often becomes a two-stroke engine with a capacity of 9.8 hp. weighing up to 26 kg, providing planing with cargo.
Installation and running of a new engine
Once you buy the engine, it must be properly mounted on a transom, the height of the lower unit mount is adjusted so that the anti-cavitation plate is parallel to the bottom of the boat or slightly buried, improper installation will lead to cavitation, loss of speed and overheating of the engine.
Particular attention should be paid to running in. This is the process of grinding engine parts, which directly affects its future life. For two-stroke engines, the break-in is usually 10 hours, during which you can not give full gas. The breaking in mixture is often made slightly richer in oil than the manufacturer recommends for normal operation.
☑️ Checklist before first launch
During the break-in, you need to periodically change the angle of inclination of the lower unit to develop all the positions. After the first 10 hours, be sure to replace the oil (in the 4T) or do the TO (in the 2T), as the oil will be a lot of metal shavings from laundry.
⚠️ Warning: Starting the engine without immersion in water or without connection to the external cooling system (barrel) is prohibited - this will lead to instant overheating and deformation of the head of the unit.
If you are not sure of your abilities, the first start and configuration of the carburetor is better to entrust the specialists of the service center.
Operation and care of the outboard motor
The durability of the motor depends not only on the quality of the assembly, but also on the correct care. After each release to the water, especially in salt or dirty water, the engine must be washed with fresh water, using special washing fittings or simply rinsing carefully.
When stored in the off-season, the engine must be preserved: old oil is drained, the cylinders are treated with a conservation mixture, and the fuel system is free of gasoline. Gasoline is oxidized when standing for long periods of time and forms resins that clog the carburetor's jelly.
How to store the engine in winter?
The motor should be stored upright in a dry room, if this is not possible, it is allowed to store on the side, but only on a certain side (specified in the instructions) so that the oil does not leak into the combustion chamber.
Check the condition of the lower unit regularly for impacts on underwater objects. Even a small dent in the lower unit can disrupt the flow of cooling water, which will lead to overheating. Temperature monitoring This is a habit that will save your engine from major repairs.
Keeping simple rules in place and replacing candles, fuel filters and pump impellers on time will keep the engine running for decades, and remember that prevention is always cheaper than repair.
Can I put a 15 hp engine on a 320 cm boat?
Technically, it is possible to set it, but 320 cm PVC boat manufacturers rarely certify them to power more than 10-12 hp. Excessing power will lead to an excessive load on the transom, the risk of its separation and loss of boat stability at speed.
What is the best gasoline to use for a motor?
For modern two-stroke and four-stroke engines, it is recommended to use AI-95 gasoline with an octane number of at least 95. The use of fuel with a lower octane number can cause detonation and damage to the piston group.
Should I drain oil from a 2T engine for the winter?
The mixture itself is mandatory, because it is layered and spoiled. The oil does not drain from the two-stroke motor crankcase, because it is not there (it burns with gasoline). In a four-stroke engine, it is desirable to change the oil for the winter, so that the acid residues of combustion are not corroded parts.
What if the engine doesn’t start after winter?
It's probably the old fuel mix that clogged the carburettor, or the candle, so try to twist the candle, clean it or replace it, blow the fuel system and pour fresh gasoline, and if it doesn't work, you need to clean the carburettor.