The transition to a jet propulsion system for inflatable boat owners is often not just a desire to experiment, but an urgent need dictated by the conditions of operation. PVC The water can solve the problem of protection of the propeller and allows you to overcome areas only 15-20 centimeters deep, which is absolutely not available for traditional outboard motors.
However, water-jet inflatable floor or hard floorboard requires a serious approach to calculating power and weight balance. The owner must understand that the water jet propulsion system is a system where the efficiency is lower than that of the propeller, and therefore the requirements for the propeller are not limited to the engine. motor-power The wrong choice of thrust will lead to the boat barely crawling, wasting fuel.
In this article, we will discuss in detail the technical nuances, consider the compatibility of various models of motors with water jet nozzles and discuss the real benefits of such a bundle for fishing and recreation. Loss of traction on water can reach 30% compared to the screw, and how to minimize this effect competent layout.
The principle of operation and advantages of jet drive on an inflatable boat
Unlike a propeller, which pushes water backwards to create jet thrust by the pressure difference, a water jet propulsion system sucks water through the inlet and ejects it through the nozzle at high speed. PVC-boat This means that people are completely safe in the water and there is no risk of damage to the screws on the bottom, and the structure has no protruding parts below the bottom level, which is critical for shallow water.
The main advantage is the ability to walk, you can walk where others are afraid to even lower the engine. Water-gun nozzle It allows you to walk on slurry, grass and stones that would instantly wind on the screw of a conventional pendant, and the lack of vibration and less noise make this boat an excellent choice for hunting or careful fishing.
But it has its own features: the jet drive is less efficient at low speeds and when trolling; if you want to be slow and fuel efficient, the classic propeller may be more economical; but there are few alternatives to speeding through shallow water.
⚠️ Attention: When operating jet drive at high speeds, the risk of foreign objects entering the inlet increases dramatically, which can lead to a jamming of the impeller. Always inspect the water area before accelerating.
Before the first launch, be sure to check for no gaps between the jet drive hull and the transom of the boat - any vibration can quickly destroy the PVC fabric.
Motor choice: power and compatibility
Engine selection is the foundation of the whole system. Because the jet propulsion system has lower efficiency, to achieve the same speed as the propeller, you will need a motor with a margin of power. For inflatable boats with a length of 3-4 meters, the best choice will be to use the engine for the engine. two-stroke power from 9.9 to 15 hp depending on the load.
Many of the companies choose Japanese brands, such as Tohatsu or YamahaBecause of their reliability and the wide range of water jet nozzles. Hidea or ParsunThey also offer solutions, but they require more careful control of the quality of assembly and fitting of the units. It is important to consider the weight of the engine: the water jet system itself is heavier than the screw group, which shifts the center of gravity.
- 🚤 9.9 hp Minimum comfortable power for boats up to 3.2 meters long with one passenger.
- 🚤 15 hp - the optimal choice for boats 3.5-4 meters, providing planing even with full load.
- 🚤 20bhp and higher - makes sense only for large PVC catamarans or boats with a rigid hull, as on small boats this will lead to transom overload.
Do not chase for maximum power if your boat is not designed for such loads. Train boat It can not withstand the vibrations and weight of a powerful motor with a jet drive, which will lead to deformation or breakage of the bottom. Always check the product passport, which indicates the maximum allowed power.
Design features of PVC installation
Mounting a water jet propulsion system on an inflatable boat is different from mounting a rigid boat. The main challenge is to ensure the rigidity of the attachment and tightness. Water passing through the channel creates significant vibrations that the soft bottom of the PVC must extinguish without losing shape.
The water jet engine itself is mounted as standard through a lower unit, but the length of the lower unit may require adjustment. If the lower unit is too short, the jet drive inlet will be too high and the motor will start to grab air ("cavitate") even on small waves, in which case the boat transom has to be built up or use special expanses.
| Parameter | Screw motor | Water-guide | Impact on the boat |
|---|---|---|---|
| Depth of immersion | 30-40 cm | 10-15 cm | Shallow water permeability |
| Weight of kit | Basic | +15-20% by weight | Shifting of the centre of gravity |
| Security | Risk of injury | Safe. | Bathing next to the boat |
| Efficiency of the system | Highly | Medium. | Fuel consumption |
Special attention should be paid to the intake hole, which is often placed below the bottom on inflatable boats, using special hydrodynamic linings, or integrated into the design of the jet drive itself, which is attached directly to the transom.
Traction calculation and speed specifications
Expectations and reality are where the frustrations of beginners are most often, and many people expect that with a jet drive, the boat will fly faster, because there is no propeller resistance, but the physics of the process dictates its conditions. Jet propulsion It's different, and it takes more energy to make it, and a boat with a jet drive is usually 10 to 20 percent slower than a similar propeller engine with the same power.
The most important parameter is the diameter of the nozzle. A narrow nozzle gives you more jet speed but less water performance, which is good for light boats. A wide nozzle increases thrust at low speeds but reduces top speed. For medium-sized PVC boats, a 110-120 mm nozzle is considered optimal.
Why does the speed drop at full gas?
At high speeds, the jet drive can start sucking air from the surface of the water if the inlet is not plugged enough, a phenomenon called cavitation that causes a sharp drop in thrust and overheating of the motor.
The weight of the crew and the load is also important. Water-gun systems are more sensitive to overload than screw systems. If you plan to take trophies or multi-day alloy gear on board, the engine power reserve must be substantial, otherwise the boat will simply not go sleeve.
Operation and maintenance
Caring for a jet propulsion system doesn't require supernatural effort, but it has its own specifics: After each step out onto the water, especially on a muddy or grassy river, you have to wash the inner chamber with fresh water, and the moisture and organic matter that's left inside can cause metal parts to corrosion or smell bad.
Check the status of the impeller (workwheel) regularly. Even small chips on the blades reduce the efficiency of the entire system. If you hear a foreign knock or vibration, immediately turn off the engine and conduct an inspection. It is not uncommon for a large stone to hit the jet drive, and further work can destroy lower unit.
- 🔧 Lubricate the bearings of the propeller shaft according to the manufacturer's regulations (usually every 50 motor hours).
- 🔧 Check the tightening of the bolts attaching the nozzle to the lower unit - vibration has the property of weakening them.
- 🔧 Examine the entrance grille for dents that may disrupt the flow of water.
⚠️ Attention: Never run a motor with a jet drive out of the water or with a lower unit raised for more than a few seconds. The lack of cooling water will cause the pump to overheat instantly and jam.
☑️ Seasonal jet drive service
Security and GIM regulations
Using a jet drive on a PVC boat imposes certain safety obligations. Although there is no risk of injuring the screw, the high speed of the jet ejected can injure a person in the water next to the stern, the pressure of the jet to knock off or strike.
In terms of registration with GIMS, the installation of a water jet nozzle does not require changes in the boat's documents, if the total power of the engine does not exceed 8 kW (about 10.8 hp). If the engine is more powerful, registration is mandatory regardless of the type of propulsion.
Always have a toolkit on board to quickly remove the jet drive if it jams. On some models, it only takes a few keys and the procedure takes 5-10 minutes. The ability to quickly return to the screw propulsion (if there is a spare one) or simply free the duct can save the situation away from the base.
A PVC jet drive is a trade-off between speed and cross-country, and you sacrifice your maximum speed for the ability to walk where others won't.
FAQ: Frequently asked questions
Can I make a water jet nozzle myself?
Theoretically, you can use drawings and available materials (plastic, aluminum). However, it is extremely difficult to create an effective channel profile and impeller at home. Homemade jet drives are often low efficiency and can be dangerous because of the risk of bursting the body under pressure.
Will the fuel consumption increase significantly?
Yes, the consumption will increase. Because the efficiency of the jet drive is lower, to maintain the same speed, the engine will have to operate at higher speeds than the propeller, on average, fuel consumption increases by 15-25% depending on the mode of operation and weight of the boat.
Is the jet drive suitable for sea fishing?
For the high seas and the large wave of jet drive on a small PVC boat is not recommended. With a strong keel rolling, the inlet can bare, the engine will grab air, and the control will become unpredictable, it is the ideal solution for rivers, lakes and calm estuaries.
How to clean the jet drive, if there was grass?
If the grass stopper keeps the engine from gaining momentum, it is usually enough to give full gas on the reverse (reverse) for a short time to knock out the debris. If this does not help, you will have to lift the engine and clean the channel manually. Some jet drives are equipped with hatches for quick cleaning without lifting the engine.