Choice rubber-boat It's always about finding a compromise between speed, payload capacity and owner budget. Many beginners mistakenly believe that any low-powered lightweight PVC boat will do, but reality dictates its own rules of hydrodynamics and safety. A misfitted power plant can not only not put the boat in sleeve mode, but also damage the transom or the cylinder itself.
The modern market offers a wide variety of models, from lightweight electric tractors to two-stroke lighters and heavy four-stroke units. In order not to get confused in the specifications, you need to clearly understand what tasks you buy a boat for: quiet fishing at dawn, high-speed walks along the reservoir or overcome strong waves and against the current. The right calculation traction and weight are the key to comfortable operation.
In this article, we will take a look at all the nuances of engine selection, the features of the installation on the soft transom, and give you a comparative description of popular models. You will learn why horsepower is not always the main criterion, and what to look for first.
Criteria for engine selection for PVC boat
The first and most important parameter is the power allowance specified by the boat manufacturer in the product's passport. forbiddenThe soft transom may not withstand vibrations and loads, which will lead to depressurization of the seams or engine separation. Usually for boats with a length of 2.7-3.2 meters, the recommended power is from 3 to 5 horsepower, and for models 3.5-4.0 meters – from 5 to 9.8 hp.
The second critical factor is the weight of the engine. inflatable boat With limited payload capacity, each extra kilogram on the transom shifts the center of gravity, causing the nose to pick up or, conversely, go underwater. Lightweight two-stroke engines weighing up to 10-12 kg are often the choice for single and double inflatable boats. Heavy four-stroke boats require boats with a hard floorboard floor and a reinforced transom.
⚠️ Warning: Never install the motor more powerful than the boat's technical data sheet, even if the transom appears strong. When planing, the load on the transom increases several times, and the balloon burst at speed can be fatal.
Also worth considering is the type of fuel and environmental requirements, and some regions have restrictions on the use of two-stroke engines due to the release of a mixture of oil and gasoline into the water. Four-stroke engines It's cleaner and more economical, but it's much heavier and more expensive to maintain. For most PVC boat owners, the best balance is the modern two-stroke, improved combustion system.
Power and speed modes: calculations and reality
Many users want to go straight to the gellingWhen the boat is sliding over the water rather than pushing it in front of it, it takes about 1 hp per 25-30 kg of total weight (boat + engine + crew + equipment) to enter this mode. If your cargo boat weighs 300 kg, then the 5 hp engine will clearly not be enough to plane, and you will move in displacement mode at a speed of 5-7 km / h.
For confident planing on a two-seater PVC boat, a motor of 5 to 8 hp is usually required. Engines in 9.8-9.9 hp are considered the "golden mean" for boats with a length of 3.2-3.6 meters, allowing you to reach speeds of up to 30-35 km / h with one driver. However, it is worth remembering that with increasing the number of passengers, speed will fall, and fuel consumption will increase.
The table below gives indicative speed data for various combinations of boat and motor:
| Boat length (m) | Engine power (hp) | Kit weight (kg) | Mode of traffic | Average speed (km/h) |
|---|---|---|---|---|
| 2.9 – 3.0 | 3.5 | ~200 | Transitional/Gleess | 18 – 22 |
| 3.2 – 3.4 | 5.0 | ~250 | planing | 24 – 28 |
| 3.5 – 3.8 | 9.8 – 9.9 | ~350 | Confident plane | 30 – 35 |
| 4.0+ | 15.0+ | ~450+ | Full plane | 38 – 45 |
It is important to understand that screw-step It also affects speed and traction. For heavy boats or cargo, smaller pitch propellers are better suited, which give more traction at low speeds. For speedy walks with minimal load, larger pitch propellers are installed. Experimental screw selection allows you to squeeze maximum performance out of the engine.
Two-stroke vs. four-stroke: the eternal dilemma
The controversy between the 2T and 4T proponents has been going on for years. rubber-boat The main argument against four-strokes is their weight: even the lightest 4T engine weighs about 20-25 kg, which can be critical for a small inflatable boat, while a two-stroke equivalent of the same power can weigh only 10-12 kg, making it easy to carry to one person.
On the other hand, four-stroke engines work quieter, more stable at idle speeds and do not require the preparation of a fuel mixture. Two-stroke engines They need to mix gasoline with oil in a strict ratio (usually 1:50 or 1:25 for older models), which creates additional oil vapors and a characteristic smell. However, modern two-strokes with E-TEC or similar technologies burn fuel almost as cleanly as four-strokes.
The myth of the reliability of two-stroke engines
There is a common belief that two-stroke motors are less reliable. In fact, thanks to their simple design (no valves and no oil crankcase), they often end up being more durable than four-stroke engines when properly maintained, the key is not to overheat and get a good lubrication.
If you plan to use a boat for trolling, the 4T engine will be more comfortable with smooth thrust at low speeds, but if your goal is to get to the catch point quickly, unload and return, the light 2T engine will save you energy during loading and unloading and provide the necessary dynamics.
Features of the installation of the motor on a soft transom
Installing the engine on an inflatable boat has its own nuances related to the elasticity of the material. Unlike rigid aluminum or fiberglass transom, PVC can bend under the weight of the engine, especially in the wave. squirt-board (lats) that distribute the load over a larger area and prevent the balloon from squeezing.
The motor is fastened by rods, which must be equipped with soft rubber linings. The metal of the rods must not (touch) the fabric of the cylinder. The rods must be tightened with sufficient force to fix, but without fanaticism, so as not to damage the structure of the PVC. Regularly check the puff during operation, as vibration can weaken the mounts.
- 🛠️ Make sure that the engine anti-cavitation plate is located parallel to the bottom of the boat or slightly lower (by 10-20 mm).
- 🛠️ Check the inclination angle of the daydvut: it should be such that the exhaust gases go into the water, and not under the bottom.
- 🛠️ Use a safety cable, run through the rings of the boat and fixed to the engine, in case of separation of the rods.
Special attention should be paid to the height of the installation. If the engine is fixed too low, water resistance increases and the risk of flooding the wave into the exhaust hole. Too high installation will lead to the screw sucking air and loss of traction. The optimal depth of immersion of the anti-cavitational plate is 10-20 mm from the conventional bottom of the boat.
☑️ Check before the first launch
Electric motors: a quiet alternative
In recent years, it has gained popularity. electric motors Their main advantages are absolute quietness, no vibration, environmental friendliness and the ability to use in places where gasoline is prohibited, such engines are ideal for fishing in shallow water, in reeds or in water bodies with strict environmental control.
But electric power has its limitations, and the main one is its range, which is directly dependent on battery capacity. Lead acid batteries are heavy (12 to 20 kg), negating the advantage of a light motor. Lithium iron phosphate (LiFePO4) batteries are lighter and capacious, but much more expensive. In addition, the maximum speed of electric motors rarely exceeds 5 to 7 km/h.
An electric motor does not require complex maintenance: no candles, filters, oil and carburetors. After the season, just rinse with fresh water and properly preserve the battery. For small boats up to 3 meters long and up to 1 hp (equivalent), electric motors are an excellent choice for a relaxing holiday.
⚠️ Warning: When using an electric motor, be sure to monitor the battery level. Sudden discharge in strong currents or winds can leave you without maneuver, as paddle with an inflatable boat with an installed engine is extremely difficult.
Maintenance and conservation of the outboard motor
The durability of the engine depends on the quality of service. For two-stroke engines, the quality of the fuel mixture is critical. The gasoline must be fresh (no older than 1-2 months), and the oil must meet the TC-W3 specification. The old fuel is oxidized and forms resins that clog the carburetor's jelly and disable the engine.
After each operation, especially in salt water, the motor must be washed with fresh water, special nozzles are placed on the water intake hole, flushing allows salt, sand and silt to be removed from the cooling system, preventing corrosion and overheating. Winter conservation involves draining fuel from the carburetor and tank, as well as storing it in an upright position.
- ⚓ Regularly lubricate the hinges of the rotary mechanism and the tiller with a special water-resistant lubricant.
- ⚓ Check the state of the spark plug: black colored soda speaks of a rich mixture, white - of a poor one.
- ⚓ Check lower unit for damage and dents that may disrupt streamlining.
If you leave the boat with the motor on the water for a few days, be sure to raise the lower unit above the water level or use a special removable casing. this will prevent the screw from fouling with algae and corrosion of metal parts.
Timely replacement impeller The rubber blubbers and cracks over time, which leads to a deterioration in the circulation of coolant, and it is recommended to change the impeller every 2-3 seasons or when there are signs of overheating, even if the engine is working normally.
Frequently Asked Questions (FAQ)
Can I put the engine 9.9 hp on the boat, where it says max. 5 hp?
No, it's dangerous. The trunk and seams of the boat are not designed to handle this vibration and load, and when you get on plane, the risk of a balloon rupturing or engine detachment is extremely high, and this is a violation of safety rules and operating conditions.
Which gasoline is best used for a two-stroke engine?
The optimal use of AI-95 gasoline with an octane number of at least 95. The use of AI-92 is possible, but can lead to detonation and overheating on some models of engines. The gasoline should be fresh, without the alcohol (ethanol) that destroys rubber seals.
Do I need to run a new engine?
Yes, breaking in is mandatory for all new engines, usually 2-10 hours of work on an enriched mixture (for 2T) or at variable speeds (no more than 70-80% of the maximum), which allows parts to get lost in each other, which prolongs the engine life.
What to do if the engine is stalled at high speeds?
Most often, it's a lack of fuel or air, check the fuel filter, the condition of the candle, the integrity of the fuel hoses and the presence of air in the system, and the problem may be a wrong screw or contamination of the lower unit.