The development of remote reservoirs rich in fish often turns into a difficult navigational task due to the abundance of underwater vegetation, snags and banal insufficient depth.
Traditional propellers in such conditions quickly fail, and the risk of damage to an expensive motor becomes critical, which forces anglers to look for alternative solutions.
Exactly. water-boat It becomes a universal tool that allows you to confidently move through overgrown rivers, swamps and shallow bays, where other equipment will simply stand up.
Unlike classical schemes, the water jet propulsion system is fully protected from external influences, which radically changes the approach to the operation of the boat.
Many owners of PVC boats and metal boats are thinking about switching to water jet thrust, but do not represent all the nuances of compatibility of the hull and engine.
In this article, we will discuss in detail why. water-boat This is not just a marketing move, but a necessity for certain conditions, and how to choose the right components.
Principal differences of the water jet propulsion
The main advantage of the jet drive is the absence of protruding parts beyond the dimensions of the body, which allows you to pass sections with a depth of only 20-30 centimeters.
Water is sucked through the intake hole into the bottom and is violently ejected through the nozzle, creating a jet thrust that pushes the vessel forward.
This design does this. water-jet practically immune to grass, mud and debris, which would instantly wind on the blades of the propeller.
However, this medal has a flip side: the efficiency of jet drive at high speeds is usually lower than that of the screw, and maneuverability at low speeds requires addiction.
For shallow waters, this is a compromise that is willing to make, since the ability to pass where others do not even risk getting on the water covers all the disadvantages.
In addition, the safety of people who are near the boat in the water, when using jet drive is much higher, because the risk of being hit by blades is excluded.
It is important to understand that water-jet requires higher revolutions to get on plane, which dictates its requirements for the power of the power unit.
⚠️ Warning: When operating in shallow water, always monitor the position of the intake hole. If it is above water level, the pump will capture air, which will lead to a sharp drop in thrust and possible overheating of the engine.
Structurally, jet drives are divided into axial and mixed currents, and for heavy boats, the second option is preferable.
Axial models are lighter and simpler, but they are only effective on lightweight, high-speed housings, whereas heavy "kazak" or loaded PVC need more powerful pumps of the mixed type.
Choice of body: PVC or metal?
The question of the choice of the material of the body is especially acute when it comes to specialized equipment for shallow water.
Both options have the right to life, but their performance specifications in conjunction with the jet drive will be radically different.
PVC boats are attractive for their versatility and the ability to quickly disassemble for transportation.
There are special ones for them. water-jet-boat with a reinforced bottom and transcrete, capable of bearing the weight of the motor and pump.
The main plus is depreciation when hitting the bottom: a soft balloon extinguishes blows against stones, which saves not only passengers, but also the water jet assembly itself.
Metal boats, in turn, have incredible strength and stability.
Aluminum case is easier to equip with a full-fledged cockpit, spray protection and comfortable runduks.
However, metal boat heavier, which requires a more powerful motor to get on plane, especially with a jet drive that has less efficiency.
When choosing, you should also take into account seasonality: PVC is more sensitive to temperature changes and ultraviolet light, while metal is almost indifferent.
If you plan to fish in reed-covered ducts, where the risk of "sitting on the belly" is high, a soft bottom of PVC can save the situation better than slippery metal.
For PVC boats, it is critically important to use special water jet nozzles with an increased support area, so as not to damage the cylinders when mooring or pulling ashore.
Selection of motor power and specifications of jet drive
The successful operation of the “boat-motor-water-water-water-water-water-water-water-water-water-gathering” bundle directly depends on the correct power calculation.
Since the water jet propeller has a lower efficiency compared to the propeller, the power reserve must be substantial.
It is usually recommended to take a motor 30-40% higher than would be required for a similar boat with a propeller.
For example, if for your water-boat with a screw would be enough 15 hp, then with a jet drive comfortable planing will begin only at 20-25 hp.
This is due to hydraulic losses inside the pump and the need to create a high flow rate for efficient jet propulsion.
Modern. boat-engine Japanese and Chinese brands often have in the line special water jet modifications with a modified air intake system and a reinforced gearbox.
It is important to pay attention to the diameter of the water intake: the larger it is, the more water the pump can pump, but the greater the resistance to movement.
For shallow waters, compact pumps are optimal, which do not require a deep landing, even at the expense of maximum speed.
☑️ Criteria for motor selection
Do not forget about fuel efficiency: water jet engine at cruising speed can consume more fuel due to work at high speeds.
Therefore, the estimated range must be recalculated in the direction of reduction, planning additional fuel tanks.
Comparison of specifications: Screw vs. Watercoat
To finally determine the feasibility of switching to water jet thrust, it is useful to compare the key indicators in figures.
Below is a table showing the typical differences for a boat about 4 meters long with a 20 hp engine.
| Parameter | The propeller | Water-guide |
|---|---|---|
| Minimum depth of travel | 50-70 cm | 15-25cm |
| Efficiency at full speed | High (~70%) | Average (~50%) |
| Protection from grass | Missing. | Complete. |
| Brakeway | Short. | Long. |
| Cost of kit | Basic | +30-50% to the price of the engine |
As you can see from the table, water-jet It loses in economy and braking, but it wins where it is most important - in passability.
The braking distance at the jet drive is much longer, since a reverse jet is used for braking, which is less effective than the screw's point in the water.
This requires the driver to be more cautious and to release the gas before obstacles.
But the opportunity to pass where the screw would have long ago turned into porridge from algae, makes jet drive indispensable for certain regions.
In overgrown deltas of rivers and on taiga rivers with rolls, there is practically no alternative to jet drive.
Features of management and maneuvering
Driving a jet drive boat has its own specifics that you need to get used to, especially if your experience is based only on screw motors.
There is no classical reverse in understanding the change in the rotation of the shaft; the direction of the thrust is changed by the turn of the deflector redirecting the jet of water.
This means that at low rpm, the steering and reverse efficiency drops to almost zero, as there is no powerful jet to create a control force.
For turning on the spot or mooring, you have to constantly "gas", creating an artificial flow of water.
But on the move. water-boat It becomes very obedient and has excellent course stability.
The absence of a screw allows you to perform risky maneuvers in narrowness, without fear of catching the bottom or snag.
The secret of manoeuvring at low speed
Use short-term pulses of gas as you turn the deflector, and this will create the necessary flow to turn the boat without a set of inertia.
Particular attention should be paid to the 180 degree turn: due to the jet inertia, the reaction to the steering wheel is delayed compared to the screw.
The driver must anticipate the behaviour of the vessel and begin the manoeuvre in advance.
It is also worth noting that in shallow water with a sharp turn, short-term air absorption is possible, which will cause vibration.
Maintenance and repair of water jet systems
Despite its apparent simplicity, the water jet propulsion requires regular and competent maintenance for long service.
The main enemy of jet drive is not grass, but solid objects (stones, sand), which can damage the impeller or wear the shell.
Regular inspection of the inside of the pump after each release to the water is a mandatory procedure.
You need to monitor the condition of the sealing rings and bearings of the shaft, since the ingress of sand into the lubricant will quickly disable them.
jet drive repair Often requires a special tool to remove the nozzle and access the impeller.
In the field, the most common problem is the stuckness of large debris in the water intake grid.
⚠️ Warning: Never attempt to clean the intake hole with your hand or foot while the engine is running or even smothered but not cooled. The shaft rotation inertia can be high and the exhaust temperature is high.
For lubrication of the nodes, only the compositions recommended by the manufacturer that are resistant to washing out with water should be used.
After operation in salt water, it is mandatory to wash with fresh water through special fittings, if they are provided by the design.
Regular lubrication of the bearing unit and checking the gaps between the impeller and the pump body are the key to preserving the traction specifications of the jet drive for many seasons.
Store the boat with jet drive is better in an upright position or on a special stand to exclude deformation of the pump body.
In winter, water must be completely drained from the system, as frozen water can tear the pump body or deform the nozzle.
Security and legal aspects
The use of water jet engines imposes certain obligations on the owner in terms of safety and legislation.
Although jet drive is considered safer for people in the water, the jet of water at the exit of the nozzle has a huge kinetic energy.
The presence of people in the water closer than 5-7 meters from the working jet drive is strictly prohibited, as the jet can cause serious injuries.
From the point of view of GIMS, water jet engines are subject to registration in the same way as conventional ones, if the engine power exceeds 8 kW (about 10.8 hp).
When installing a homemade or converted jet drive, questions may arise when passing a technical survey.
Certified water-jet The factory has all the necessary documents that simplify registration.
It is also important to consider that the noise of the jet drive can be higher than that of the screw analogue, due to cavitation and pump operation.
This is worth remembering if you plan to fish in places where silence is required or in protected areas with noise restrictions.
Legal nuance
When installing jet drive on a boat already registered, you need to make changes to the boat's documentation, indicating a new type of propulsion system.
Always carry an emergency tow kit with you, as in the event of a jet drive breakage, the boat becomes almost unmanageable on the current.
The absence of a propeller does not mean permissiveness: the rules of navigation on inland waterways are the same for all types of vessels.
Can I convert a motor into a water jet?
Theoretically possible, but in practice it's complicated and risky, requiring precise flange docking, gear ratio calculation and tightness, factory kits are safer and more reliable.
What is the maximum speed of a jet drive boat?
It is usually 10-15% lower than the equivalent propeller. For light boats it is 35-45 km / h, for heavy boats - 25-30 km / h. The speed depends on the weight, engine power and type of jet drive.
Does the fish get stuck in the jet drive?
Yes, large fish can get into the pump. Modern jet drives have protective grates, but small fish and soft tin pass freely. Large objects can damage the impeller.
Do I need to change the oil in the jet drive?
There is no oil in the pump itself, it is lubricated with off-board water. However, the motor gearbox (if it remains) requires regular oil change, as in the screw version. jet drive shaft bearings require periodic lubrication.
Is it true that jet drive dies on the grass?
No, the jet drive does not die from the grass, because it passes freely through the pump, problems can only occur if the grass completely blocks the water intake, which is extremely rare due to the high flow rate.