PVC inflatable boats have long ceased to be just a means for quiet fishing in the coastal zone. Modern models are able to withstand severe loads and develop high speeds, which requires more advanced propellers. Traditional propeller, despite its effectiveness, has a number of limitations, especially when driving on overgrown bodies of water or shallow water. jet-driverIt offers unique maneuvering and safety capabilities.
The way a jet drive works is very different from the usual screw propulsion system, which is sucked in through the water intake into the bottom and ejected at high speed through the nozzle in the aft, creating jet propulsion. PVC This solution opens up new horizons: the ability to walk where a screw would instantly wind grass or hit rocks, but the transition to jet propulsion requires careful preparation and understanding of the technical nuances.
In this article, we will discuss in detail whether the game is worth a candle, which engines are suitable for remodeling and how to properly assemble the system yourself. You will learn about the real speed, fuel consumption and features of controlling a water jet vessel. The right approach to modernization will make your inflatable boat a versatile tool for all water conditions.
The principle of operation and the key advantages of jet drive
The idea behind the jet propulsion system is to create thrust by ejecting a jet of water. The motor spins the impeller, which is inside the pump body. Water enters through the hole in the bottom, passes through the rectifier, and is pushed out forcefully. The absence of external rotating parts makes the structure. safe for bathers and animals, which is critical for family holidays.
One of the main advantages is the cross-country ability, which is located on the bottom plane, allowing you to overcome areas with a depth of only 15-20 centimeters. For comparison, even the shortest lower unit outboard motor requires a minimum of 30-40 cm to work normally without the risk of cavitation or impact, which makes the jet drive ideal for deltas, overgrown lakes and shallow estuaries.
And the water jet engine also doesn't have the cavitation effect of plane in sharp turns, because the impeller is always in the water flow, even if the boat is tilting very hard, and it's very stable at high speeds, but it's worth remembering that the efficiency of the water jet is lower than that of the propeller, so acceleration can be more sluggish.
⚠️ Attention: When you're driving a jet drive at low speeds, the efficiency of the steering is reduced as the stream of water around the steering wheel becomes weaker. Be careful when mooring in windy weather.
Other advantages include the protection of the mechanism from impacts on floating objects: rocks, snags and drowners are rarely sucked into the water intake due to a protective grille, and if they do get inside, they most often pass through the impeller without breaking the blades, unlike a screw, which can get chipped or cracked.
Comparison with propeller: specifications table
Before deciding to re-equip your PVCWe need to make an objective assessment of the difference between a traditional propeller and a jet drive, and each type of propeller has its own niche, and the propeller remains the king of efficiency in deep water and heavy loads, whereas the jet drive is the king of shallow water and maneuverability.
It is important to consider that when you install a jet drive on a standard motor, you lose some of the power due to hydraulic losses in the channel. Usually, the losses are from 10 to 20% of the original engine power. So to achieve the same speed as the propeller, you may need a higher power motor or lighter boat design.
Below is a comparative table that helps you decide on the choice of propulsion depending on your priorities and operating conditions.
| Parameter | The propeller | Water-guide |
|---|---|---|
| Passability (min depth) | 30-40 cm | 10-15 cm |
| Protection against garbage | Low. | High. |
| Full speed efficiency | High (baseline) | Average (loss 10-20%) |
| Safety of people | Danger zone at the rear | Safe (no external blades) |
| Reverse (reverse) | Effective. | Less efficient (depending on design) |
As you can see from the table, the jet drive loses in pure efficiency, but it wins in specific conditions. If your main scenario is a quick delivery from point A to point B on a deep channel, the screw will be more economical. If you like to explore unknown ducts, fish in reeds or ride with children near the shore, the jet drive will provide an unmatched level of comfort and safety.
Choice of motor for jet drive installation
Not every outboard motor is suitable for conversion to a water jet. The main requirement is the ability to dock with a water intake device. Most often, the popular two-stroke and four-stroke engines with a capacity of 5 to 15 hp are reworked. PVC with passengers.
The most popular base for creating water jet sets are motors Yamaha, Tohatsu and MercuryTheir lower unit design makes it relatively easy to dismantle a standard screw and gearbox, replacing them with a water intake adapter. It is important that the motor has a sufficient power reserve, since the jet drive eats up some horsepower.
When choosing a motor, you should also pay attention to the cooling system. In water jet mode, the motor continues to receive water for cooling through the normal holes, but the pressure in the system may change. Some masters recommend installing additional filters-grids on the inlet cooling holes to prevent sand from entering, which can abrasively wear out the cooling pump.
⚠️ Note: The use of electronically controlled (Fly-by-wire) motors for homemade jet drives can be difficult due to the difficulty of coordinating the operation of the jet drive reverse flap with the motor electronics.
For PVC The optimal power range is 9.9 - 15 hp Motors in 5-6 hp will be able to bring to the glise only a single boat with minimal load, and 20-30 hp will require a very rigid and large inflatable vessel to withstand the increased dynamic loads and weight of the water jet nozzle.
Technology of installation of water jet nozzle DIY
Installation of jet drive PVC There are two main ways to do this: buy a ready-made attachment complex or make a water intake yourself, both of which are the keys to keeping the motor and the water intake tight, and to properly align the shafts.
If you use a ready-made kit, for example, from Russian or Chinese manufacturers, the instruction usually involves removing the standard lower unit, in its place is installed a transition plate to which the jet drive body is attached, it is important to ensure that the flanges are tightly fit to eliminate the air suction, which will lead to cavitation and loss of traction.
☑️ Checklist of jet drive installation
In self-manufacture, large-diameter polypropylene pipes are often used or fiberglass casings are formed, and it is critical to follow the geometry of the inlet and outlet, the inlet should be wide so as not to create vortices, and the inner surface of the channel should be as smooth as possible.
Pay special attention to fastening the entire structure to the transom PVCThe weight of the jet drive with the water inside is significant, and there are vibrations when you move. Using only regular engine rods may not be enough. It is recommended to use additional safety ropes or reinforced brackets to prevent the loss of expensive equipment.
The secret of success in the manufacture of homemade jet drive
The key secret is the shape of the nozzle. The narrowing of the outlet (cone) increases the speed of the outlet jet, which directly affects the thrust, but too much narrowing will create excessive pressure on the motor, so the optimal cone angle is selected experimentally, usually in the range of 10-15 degrees.
Operation and maintenance of the water jet engine
jet drive care is easier than a screw motor, but it has its own peculiarities. The main problem of waterways is algae and sand. Although the water intake grid protects the impeller, small fractions of sand and silt can accumulate inside the channel, creating growths and disrupting hydrodynamics. Regular flushing with fresh water after each exit is mandatory.
The impeller (work wheel) is the heart of the system. The gap between the impeller blades and the pump body should be minimal (usually 0.5-1 mm). The wear of this gap leads to a sharp drop in efficiency. Periodically check the condition of the blades: they should not be chipped, deep scratches or deformations.
During operation, PVC It's important to remember inertia. The water jet can't change the direction of thrust instantly. The switch from full-forward to full-back (reverse) is by lowering the deflector (flipper) that redirects the jet. This takes a fraction of a second, but at high speed, the braking distance will be longer than the screw counterpart.
⚠️ Warning: Never run a motor with a jet drive out of the water or with a water intake raised above the water for longer than a few seconds, which will overheat and destroy the sealing ossuaries.
It is also worth monitoring the condition of rubber elements. PVC Vibrations from the jet drive may differ from screws, and regularly inspect the place of attachment of the transmolina and cylinders for scuffing or relaxation of tension.
Influence of jet drive on the running performance of the PVC boat
jet drive installation changes the behavior of the boat on the water. Due to the lack of a persistent propeller bearing and a change in the thrust vector, the boat can become more sensitive to load skewing. PVC More importantly, moving passengers or cargo on board can lead to a noticeable departure of the boat.
In the planing, the jet drive boat is very smooth, because there is no vibration from the propeller. However, the plane can be more prolonged. To compensate for this effect, many water engines use the "jump" technique: a short-term sharp addition of gas helps to quickly remove the transom from the water.
To improve the getting on plane with a jet drive, try to slightly raise the nose of the boat, shifting the load closer to the stern, or use transom plates (if the design of the boat allows their installation).
Maximum speed PVC With a jet drive, it's usually 10 to 15 percent lower than a propeller of the same power, but if you consider the ability to keep the full gas where the propeller would have to slow down because of grass or rocks, the average route time can be even less.
Frequently Asked Questions (FAQ)
Will the speed of the boat drop after installing the jet drive?
Yes, the speed drop is inevitable because of hydraulic losses, and on average, the loss is 3-5 km/h on 9.9-15 hp engines, but on overgrown bodies of water, your average speed can increase, since you do not have to constantly clean the propeller.
Can I install a jet drive on an electric motor?
Theoretically, it's possible, but it's not economically feasible: the water jet requires high revs to create pressure, which will quickly land the battery, and for electric motors, it's more efficient to use special low-noise screws.
Do I need to register a rework in GIMS?
Under current regulations, changing the propulsion type (from screw to water jet) is a change in the design of a small vessel, which formally requires changes in documents, although in practice inspectors rarely pay attention to this if the engine remains the same power.
How often should I change the impeller?
The life of the impeller depends on the operating conditions. It lasts for years on clean water. When you move frequently on the sandy bottom or in water with abrasive suspension, the gaps should be checked once a season, and replacement should be done as they wear out (usually 200-300 motor hours).
The water-jet engine is a specialized solution for shallow water and safety, which sacrifices maximum speed and efficiency for the sake of cross-country and security.
In summary, we can say that the water jet engine on the PVC It's a great choice for those who value versatility and safety, and despite some of the speed losses, the opportunities that come with a hydraulic motor often outweigh the disadvantages, and the right equipment and the right installation will allow you to enjoy water walks in all conditions.