Choosing a power unit for an inflatable boat is always a search for a compromise between the desired speed, load capacity and weight of the equipment. Motor to the inflatable boat Not only must it be powerful enough to get the boat to sleeve, it must also be safe to operate with PVC tubes, and a miscalculation can lead to the transom breaking up or, worse, to a water emergency.
The current market offers many options, from lightweight electric tractors to powerful two-stroke fuel units. It is important to understand that there is no one-size-fits-all solution: quiet fishing on the lake and high-speed fishing require completely different specifications. In this article, we will discuss all the nuances that will help you make an informed decision.
Types of engines: electricity or gasoline?
The first thing that the owner of the boat faces is the dilemma of choosing the source of energy. Electric motors They're ideal for people who appreciate silence and exhaust odorlessness, they're easy to maintain, they don't require oil change or fuel mix preparation, but they're limited by battery capacity, and they rarely go beyond 5-7 km/h, making them suitable only for displacement.
Gasoline engines, in turn, give you complete freedom of movement, they are able to accelerate the boat to 30-40 km / h and above, allowing you to travel long distances and get on plane. two-stroke and four-stroke Two-strokes are lighter, cheaper and easier to transport (you can carry on your side), but they are noisier and require a mixture of gasoline and oil.
⚠️ Warning: Never use pure gasoline in a two-stroke engine without adding a special oil, which will result in instant jamming of the piston group and expensive repairs.
Four-stroke units are more economical, quieter and more environmentally friendly, but they are much heavier than their two-stroke counterparts. For a lightweight inflatable boat weighing 20-30 kg, a four-stroke engine can become an anchor that is difficult to lift on board and which will shift the center of gravity of the stern.
- 🔋 Electric motors: quiet, light, require charging batteries, low speed.
- ⛽ Two-stroke petrol: powerful, light, noisy, require a mixture of fuel.
- 🚜 Four-stroke petrol: economical, quiet, heavy, reliable.
Power calculation and compatibility with the boat
The key parameter in the selection is motor-powerThe PVC boat manufacturer always indicates the maximum permissible engine power in the product passport, exceeding this liment is strictly prohibited, since the pressure on the transom during plane can tear the material or break the mounting board.
There is an average formula for calculating: to get on plane one person weighing 80 kg, it takes about 1 hp of power for every 25-30 kg of total weight (boat + engine + equipment + passenger). However, inflatable flat-bottomed boats (NPB) plane occurs later than on inflatable keel boats, so the power reserve is desirable.
Let’s look at the following recommendations for different classes of boats:
| Boat length (m) | Type of bottom | Recommended power (hp) | Max. speed (km/h) |
|---|---|---|---|
| 2.7 – 3.0 | Slan/NDM | 2.5 – 5.0 | 15 – 25 |
| 3.2 – 3.6 | NDMA | 9.8 – 15.0 | 30 – 40 |
| 3.8 – 4.2 | NDNDM/Kil | 15.0 – 20.0 | 40 – 50 |
| 4.5+ | Keel/Rib | 20.0 – 40.0+ | 50 – 60+ |
For confident planing of two people on a boat with a length of 3.2 meters, the minimum engine power is 9.8 hp, optimally - 15 hp.
If you plan to use the boat alone, you may want to consider options for less power, but be aware of safety and the ability to counter current or wind. The power of the 5 hp engine is a threshold: in a number of countries (and earlier in Russia) for the control of a boat with such a motor was not required rights, but the legislation may change, and the current requirements of the GIMS must be checked separately.
Motor fastening: features of inflatable boat transoms
Installation rubberboat It's very different from a rigid hull, and it's critical to have a translator, a rigid stern insert, which is attached to the lower unit, and the traverses are built-in and removable, and they're more robust, but they add weight to the boat when assembled, and they're easy to transport, but they need to be checked carefully before they go out.
When you attach the motor, you need to monitor the depth of the propeller's immersion. If the propeller is too high, you will cavitate (air capture), which will lead to overheating of the engine and loss of traction. If it is too low, water resistance will increase. The optimal position is when the anti-cavitation plate is 1-2 cm below the bottom of the boat when moving.
☑️ Check before installing the engine
Pay special attention to insurance. Strubsins. The motor must be tightened as tightly as possible, but without fanaticism, so as not to damage the coating of the transom, but even the tightest puff does not guarantee that the motor will not fly off when hit by a wave or a log.
⚠️ Warning: Always use a safety cable (fal) run through the transom bolt and the motor handle, the only protection against loss of the engine in the event of its detachment.
The propeller: step and material
Many beginners underestimate the importance of getting the right propeller. It's the screw that converts engine power into traction. Standard propellers that come with the engine are often a compromise. Inflatable boats that have high drag often require a smaller propeller to spin to operational speeds.
The material of the screw is also important. Aluminum screws They are cheap and easy, but when hit by a hard obstacle, they bend, transferring some of the energy of the impact to lower unit. Stainless steel It's tougher and more efficient, but more expensive. composite screw or screws with a protection system (Safety Propeller), which, when hit, turn on the shaft or break, saving the gearbox.
How do you know if the propeller is not correctly selected? If the engine does not develop maximum speeds at full gas (for example, according to the instructions, 5000-5500 rpm), then the propeller is too heavy (big step). If the engine roars, reaching maximum speed, but the boat does not accelerate, the step is too small and the engine runs in vain.
- 🌀 Small step: It is better for heavy boats, towing, glides with full load.
- 🚀 Big step: It gives high speed on light boats with one passenger.
- 🛡️ Screw protection: priority for rocky rivers and shallow waters.
What is cavitation and how is it dangerous?
Cavitation is the formation of vapor bubbles in the thinning zone behind the propeller blades. When these bubbles collapse, a shock wave occurs that literally eats away the screw metal and creates a lot of noise. For the motor, cavitation means overheating due to a violation of cooling water intake.
Safety and service at sea
Operating an inflatable boat with an engine requires discipline; PVC materials are sensitive to sparks and hot surfaces; the exhaust system of the engine (especially two-stroke) can be heated to high temperatures; you need to ensure that exhaust gases do not fall directly on the cylinders, and the engine itself is reliably fixed and does not rub against the side when rolling.
Regular maintenance prolongs the life of the unit. After every fishing, especially in salt water, the engine must be washed with fresh water. For this, there are special nozzles on the intake hole, allowing you to "drive" the engine in a barrel of water or connect to a hose.
It is important to check the status of pump-membranes If the engine is running out of the control hole, if it's not running a stream of water or it's very weak, it's a signal that the cooling system is clogged or broken, and if the engine is not cooling, it will cause the cylinders to get bullied in minutes.
After operation in salt water, be sure to let the motor work 5-10 minutes in a fresh water container, adding a little oil to lubricate the internal channels if you plan long-term storage.
⚠️ Warning: Do not leave the motor in the water for a long time (more than a day) without extreme necessity. Seashelled parts and electrochemical corrosion will reduce the life of the lower unit.
Transport and storage
The question of transporting the engine often comes up in the face of car owners. Two-stroke engines can be transported in any position, but it is desirable to drain the fuel from the carburetor to avoid overflowing and filling the candle. Four-stroke models require a strictly vertical position or stacking on a specific side (as indicated in the instructions) so that oil does not get into the combustion chamber or air filter.
When storing off-season, it is recommended to treat the fuel system with a stabilizer if the engine is left without work for more than a month. Gasoline has the property of decomposing and oxidizing, forming resinous deposits that clog the carburetor's jellyplates. Engine conservation A simple procedure that takes 15 minutes, but saves from complex repairs in the spring.
For inflatable boats, the total weight of the kit is important. If you plan to throw frequent to hard-to-reach places, every kilogram counts. In such cases, it makes sense to consider lightweight Chinese-made engines or modern electric versions with lithium-iron-phosphate (LiFePO4) batteries that are lighter than lead-based counterparts.
- ⛽ Fuel drain: It is mandatory before long-term storage or transportation in the cabin of the car.
- 🧼 Washing: It is required after each release into salt water.
- 🔧 Lubricant: regularly lubricate the points of friction and rotation of the motor.
Proper preservation for the winter and regular washing of the cooling system are two main factors that ensure long service of the outboard motor.
Frequently Asked Questions (FAQ)
Can the engine be more powerful than the boat manufacturer recommends?
Excessive power will lead to excessive pressure on the transom, which can cause the seams to break, the transom to break off the cylinders or the boat to tip over at a sharp start, it is not only a matter of guarantee, but also your safety.
How often should you change the oil in the gearbox?
The oil in the gearbox (lower gear) is recommended to change once a season or every 100 motor hours. If the oil has acquired a milky shade, then the sealing of the ossels is broken and water has got into the gearbox - urgent repair is required.
Which gasoline is best used for a two-stroke engine?
The recommended gasoline is an AI-92 or an AI-95 with the octane number specified in the instructions, the main thing is the freshness of the fuel. Gasoline that has stood for more than 2-3 months loses its properties and can cause problems with starting.
Do I need to register a boat with a 5 hp engine?
The legislation is changing. Currently, vessels with an engine of more than 8 kW (about 10.8 hp) or if the weight of the curb vessel exceeds 200 kg are subject to registration in the Russian Federation. However, the availability of control rights is required when the engine power is more than 10 hp. Always check the current rules at the local GIMS office.