The waters open up anew when standard outboard motors become scarce or restricted to conservation areas, and it is at these moments that many inflatable watercraft owners think about building or buying. PVC boat-plantThis solution allows you to overcome shallow waters, overgrown with mud areas and even go to hard ground, which is not available to classical screw propulsion.
The design of the propeller, enclosed in a protective ring, radically changes the performance of the vessel. The lack of protruding parts under water makes such a unit ideal for fishing in reeds and hunting in marshy terrain. boat It requires a special approach to balancing and management.
Unlike traditional motors, thrust is created by throwing away a huge mass of air, which creates a specific acoustic background and wind flow. jet-plant It can accelerate a lightweight inflatable boat to impressive speeds, but errors in calculations can lead to instability on the course, and we will then detail how to design, assemble and safely operate this unique form of water transport.
The principle of operation and advantages of air engines
The basis of any air-plant It's a propeller that creates a jet propulsion that goes backwards. When you spin at high speed, the blades grab air and force it out the opposite direction of the propeller. Newton's third law says that this action causes a resultant force to push the boat forward. The efficiency of this propulsion at low speeds may be inferior to the propeller, but in glides, the difference becomes less noticeable.
The main advantage is that you're completely independent of the depth of the dive. blades It's going to hit a snag, rocks or bottom, and that makes it indispensable for research in shallow waters where a normal motor will instantly fail, and the lack of vibration from the rotor in the water reduces the noise inside the cockpit, even though the external noise from the engine is still high.
Structurally, the installation consists of an engine, a gearbox (often with a belt or chain drive), the screw itself and a protective fencing. Protective ring It is critical not only in safety but also in aerodynamics, preventing flow from the ends of the blades. For PVC boats, the absence of exhaust gases in the vicinity of passengers is also an important factor if the exhaust is directed up and forward, although the wind can blow them back.
⚠️ Attention: The direction of exhaust gases should be strictly calculated taking into account the winds when driving. Incorrect orientation of the silencer can lead to carbon monoxide poisoning of people sitting on the boat.
The efficiency of the operation depends on the pitch of the screw and its diameter. Too large a diameter will create excessive torque, which can destabilize a light inflatable boat. Small diameter will not provide the necessary thrust to enter the planing. propeller This is the first step in designing.
Selection of power unit and calculation of thrust
The heart of your future aeroplant will be the engine, and most enthusiasts will use motorcycle engines, snowmobile engines or specialized aircraft models, the power must match the displacement of a full-load boat. A single inflatable boat can be 10-15 hp, whereas a two- or three-seater will require 25-40 hp or more.
The most important parameter is the weight of the engine. air propulsion unit It's mounted on the stern, and any excess weight there can lead to differentiation on the stern, which dramatically worsens driving performance and safety. Lightweight two-stroke engines here beat heavy four-stroke counterparts, despite greater fuel consumption and noise.
The thrust is calculated using complex aerodynamic formulas that take into account air density, screw diameter and rotational frequency. Simply put, thrust is proportional to the square of the screw diameter and the square of the rotational frequency. However, in practice, it is important to take into account the loss in transmission. The belt gear, for example, eats some power, but allows you to reduce the speed of the screw to optimal.
The following engine type comparison table can be used to select components:
| Type of engine | Weight (kg) | Power (hp) | Features |
|---|---|---|---|
| Motorcycle (IZH, Ural) | 35-45 | 28-36 | Availability, maintainability, high noise |
| Snowmobile (Yamaha, Buran) | 40-60 | 40-60 | High reliability, availability of a variator, high weight |
| Aviation (Rotax) | 25-35 | 50-80 | High price, low weight, high efficiency |
| Automobile (Oka, VAZ) | 70-90 | 30-50 | Low cost, heavy weight, difficulty cooling |
When choosing a motor, consider the cooling system. Water cooling on an aeroplant is more difficult to organize than on a conventional engine, since water withdrawal must be carried out separately. Air cooling is easier, but requires efficient blowing, which can be problematic at low revs.
Design of propeller and protective guard
The screw is the most important element. For PVC boats, screws with a diameter of 1200 to 1800 mm are usually used. The material of the blades can be different: wood, aluminum or composite. Wooden screws It's easier to make at home, it's easier to repair, but it's afraid of moisture and it needs to be varnished carefully. Aluminum is stronger, but when it hits a hard object, it can break down the gearbox because it doesn't have the elasticity.
The protective ring (fairing) is made of fiberglass, carbon fiber or thin aluminum, and its task is not only to protect against contact with the blades, but also to form a flow. The gap between the blade and the ring should be minimal (3-5 mm) to reduce air flow and increase efficiency. However, for a homemade installation on a PVC boat, a gap of 10-15 mm will be safer.
The screw attachment to the shaft should be exclusively conical with veneer or slate, as in aviation. A threaded connection without a cone is unacceptable because of the risk of self-unwinding under load. The screw balancing is a mandatory procedure. The imbalance will cause a severe vibration that will quickly destroy the engine bearings and can damage the cylinders of the boat.
Paddle materials
Wood (pine, oak, ash) requires careful drying and protection with varnish. Aluminum alloys (D16T) are good for cleaning, but difficult to mold. Composites (carbon, fiberglass) are ideal in weight and strength, but require complex tooling to make.
When making a propeller yourself, it is important to observe the geometry of the blade profile. The profile should be aerodynamic, like the wing of an airplane. Sharp edges and irregularities will create turbulence and noise, reducing the efficiency of the entire operation of the entire aircraft. jet-system.
Inflatable board anchorage
Installation of heavy construction on the soft side PVC A simple twirling of the transom to the cylinder would not withstand vibration and weight, a rigid frame (frame) should be used to distribute the load over a large area of the board, usually made of dural pipes or profile pipe, lined with plywood.
The frame is attached to the cylinders through special "ears" or areas glued to the cylinder. The contact area should be maximum. Between the rigid frame and the soft sides must be laid damping material, such as thick transporter tape or rubber, to prevent rubbing.
The center of gravity of the installation should be as low and close as possible to the diametrical plane of the boat. The high landing of the engine will make the boat roll. Often the engine is placed at the top of the frame and the screw is lowered lower, but this creates a lever that heels the stern. The ideal option is a horizontal shaft arrangement, with the engine and the propeller on the same line just above the side section.
☑️ Verification of the installation anchorage
The transom board, if used, should be reinforced. Standard transom boards for light motors may not support the weight of the aeroplant. It is recommended to use plywood at least 18-24 mm thick with a fiberglass coating to protect against moisture.
Governance and security
The aeroplant is different from a conventional outboard motor, there is no lower unit and rotary hub in the classic form, the rotation is carried out either by turning the entire engine along with the propeller (which is difficult to implement due to the weight and hoses), or by using air rudders installed behind the screw in the air flow.
Air rudders These are vertical plates that overlap part of the flow, creating a turning point. They connect with cables to a tiller or a steering wheel. The efficiency of the rudders increases with the speed of the propeller. At low speeds, the boat can become almost unmanageable, which requires additional thrusters or oars.
The safety system must include an emergency switch ("check") that shuts down the engine when the driver falls overboard, protection against overheating is also mandatory, especially if an air-cooled engine is used, and the temperature sensor must be displayed on the dashboard.
⚠️ Warning: Operating an aeroplant without a protective casing on the propeller is strictly prohibited. The blades, rotating at a speed of 2000+ rpm, are invisible to the eye and deadly.
The standard cable drive from a motorcycle or snowmobile is used to control the gas, and it is important to ensure smooth running of the gas handle, since a sharp opening of the throttle can lead to a sharp roll of the boat or a turn at low speed.
Operation, maintenance and tuning
After assembly and the first tests, the adjustment stage begins, often requiring adjustments to the angle of installation of the propeller or the shape of the air rudders. Service Aircraft installations are reduced to regular lubrication of bearings, check the tension of the chain belts and control of fasteners. Vibration is the main enemy, so once a season it is recommended to stretch all the bolts.
In winter, storage requires engine dismantling and careful preservation. Rubber elements (belts, Silent blocks) are better stored in warmth so that they do not crack. The PVC boat itself should be stored in an inflated state or properly folded so that the frame attachments do not deform.
Tuning is often designed to reduce noise and increase efficiency. Installing a resonator muffler can significantly reduce acoustic discomfort. Using composite screws instead of wood allows you to adjust the pitch more accurately and reduce weight. Some owners install deflectors to remove exhaust gases higher and further from passengers.
To reduce noise and improve safety, a stainless steel mesh screen can be installed on the screw, which will protect the screw from hitting large objects (birds, branches) and reduce the risk of injury, although it will reduce traction slightly.
Remember, the aeroplant changes the center of gravity of the boat, you need to watch the differentiation when loading things or passengers, if the stern is too submerged, the speed drops, and the fuel consumption increases, and moving the cargo forward can fix the situation.
The key to the success of the aeroplant is the balance between engine power and mounting strength, and overloading the PVC transom of the boat leads to rapid destruction of the cylinders.
Frequently Asked Questions (FAQ)
Do I need to register an aircraft in GIMS?
Under current Russian law, registration is required for small vessels weighing more than 200 kg complete with an engine. If your PVC boat weighs less than 200 kg with an installed aeroplant and engine, registration is not required. However, if the engine power exceeds 8 kW (about 10.8 hp), driving rights may be required even if the weight is less than 200 kg (you need to specify the current amendments to the Administrative Code and GIMS rules for the current year).
What is the maximum speed of a PVC boat with an aeroplant?
Speed depends on engine power, boat contours and loading. A light single boat with a 15 hp engine can develop 35-45 km / h. More powerful installations (40-50 hp) on double boats are able to accelerate to 60-70 km / h. However, inflatable sides create sailing, which limits the maximum speed in the wind.
Can I use the air propulsion unit in the winter?
Yes, this is one of the main advantages. Airships are often used as snowmobiles on ice and snow. However, PVC material becomes hard and brittle in the cold, you need to use special frost-resistant boats (made of Hypalon fabric or reinforced PVC) and be extremely careful when in contact with sharp ice. The engine must also be prepared for winter operation.
Is the air propulsion setup making too much noise?
The noise level is much higher than that of a four-stroke outboard motor, comparable to a motorcycle or chainsaw, the main source of noise is exhaust and aerodynamic rotor noise, the use of silencers and soundproofing casings is necessary for comfortable operation, especially when hunting, where noise can scare away game.