The dream of fast and inexpensive motorization of a small boat or catamaran is often broken by the high prices of specialized outboard motors. In search of an alternative, many home craftsmen turn to garden equipment, namely, the use of a large number of outboard motors. petrol trimmerThe idea seems brilliant in its simplicity: to use an existing powerful engine, adding a special screw and a lower unit, but to implement such a project requires a deep understanding of mechanics and hydrodynamics, so as not to get just a wet and noisy design.
Concept of use two-stroke From lawn mower for movement on water is not new and has the right to exist, but only with a competent engineering approach. outboard motor nozzle It should be perfectly docked with the trimmer shaft, transmit torque without beats and, most importantly, provide reliable water cooling or have an efficient air blowing system, errors in calculations lead to overheating of the piston group in minutes.
In this article, we will discuss in detail what such a nozzle is, how it interacts with trimmer And we're going to look at the technicalities that beginners often miss when trying to adapt a land tool to the water element, and the right components are the key to ensuring that your boat will float and your engine won't jam in the middle of the water body.
The principle of operation and design of homemade jet drive
The basis of any such design is gearboxIt's the one that takes the main load, transferring the power from the trimmer engine to the propeller. Unlike the standard mower head, it requires tightness and the ability to operate in aggressive aqueous environments without losing lubrication. taperedIt must be made of high-quality steel.
The second critical element is the cooling system, and because most trimmers are air-cooled, they don't get enough air flow when they're installed on water because of the design of the casing and the proximity of the water. outboard motor nozzle Often comes with an additional intake housing that directs the flow of off-board water to the hot parts of the engine, or requires forced ventilation, ignoring this aspect leads to instant overheating.
Why can’t you use a regular head?
Using a standard head with a fishing line or even a metal knife in water is ineffective because of the low density of water compared to grass. the efficiency of such a "engine" will tend to zero, and the risk of damage to the shaft due to water resistance is maximum.
The third component is itself. propellerIt has to have a pitch and a diameter that corresponds to the speed of the trimmer engine. Too big a screw will put an excessive load on the crankshaft, and a small one will not give traction. blade-system allows you to develop a speed comparable to low-power electric motors, while maintaining the autonomy of the gasoline unit.
Engine compatibility: what trimmers are suitable
Not every garden tool can be the basis for an outboard motor. The key factor is the type of shaft: it must be the same. rigidThe flexible shaft used in light trimmers with a curved bar will not withstand the water resistance and torque of the screw, will quickly heat up and collapse, so the choice falls solely on the models with a straight bar.
Engine power is also critical: A small, one-man inflatable boat requires at least 1.5-2 horsepower to move confidently, and weaker models simply won’t be able to pull the boat into plane or even overcome strong currents. Gasoline two-stroke A volume of 33 cubic centimeters is considered the minimum threshold for such experiments.
It is important to pay attention to the mounting system. Schlitz connection The shaft should match the seat of the nozzle. Universal adapters are rare, so most often the nozzle has to be selected for a specific trimmer model or, conversely, to look for an engine under a ready-made nozzle. Stihl, Husqvarna or Karcher They have their own standards that need to be taken into account.
Technical specifications and comparison of models
When choosing or manufacturing a kit, you need to rely on dry numbers. Other nozzle models offer different efficiency, weight and compatibility. Below is a comparison table of popular solutions available on the market or assembled by hand.
| Parameter | Sail nozzle. | WaterSnake nozzle. | Homemade gearbox |
|---|---|---|---|
| Max, engine power. | up to 2.5 hp | up to 3.0 hp | materially dependent |
| Shaft type | Square 8-9 mm | Schlitz 10 teeth | Any hard-boiled |
| Rotor diameter | 180 mm | 200 mm | Individually |
| Weight of kit | 4.5 kg | 5.2 kg | 3.0 - 7.0 kg |
| Cooling | Airborne | Combined | Missing. |
As you can see from the table, off-the-shelf solutions often have a limited range of compatibility. Square shaft It is found in Chinese trimmers, while European brands use topping up connections. Homemade options allow for flexible settings, but require a high skill of the performer.
Efficiency propeller Heavy boats need a big-step propeller, but then the engine will run at its limit. Light catamarans require smaller-step propellers to quickly gain speed. outboard motor nozzle It should balance these parameters so as not to burn the engine in the first swim.
Instructions for assembly and installation on the boat
The assembly process requires precision and the right tool, and the first thing you need to do is to remove the cutting headset from the trimmer and install it. gear-knotThe shaft must be tight, without backlashes, often using a pin or locking screw to fix it, and then a lower unit (foot) with a screw is installed.
☑️ Pre-launch checks
The entire structure is attached to the boat through a tanner hanging. It is important to ensure rigid fixation, since the vibration from the boat is very strong. combustion engine Wood bars are often used as gaskets between the metal clamp and the boat cylinder to avoid damaging the PVC material, and the tilt angle of the lower unit is adjusted to achieve optimal screw deepening.
⚠️ Attention: Before starting, make sure to check whether the gas cable or the engine stop lever has twisted. Vibration can shift the controls, leading to an uncontrolled set of revolutions.
The engine is started in standard mode, but with mandatory exhaust control. Exhaust gases should not get into the boat or under the awning, as they contain carbon monoxide. outboard motor nozzle frequently changes the position of the exhaust pipe, so it may be necessary to extend the exhaust system or install a drain.
Operation and safety measures on water
The water element does not forgive mistakes, especially when it comes to homemade devices, the main rule is always to have a backup mode of movement, such as an oar. Gasoline trimmerA steroid that's converted into a motor can fail at any time because water gets into a carburetor or a candle, and the reliability of this system is lower than that of specialized outboard motors.
Watch the engine temperature. If you smell burning or see the engine losing power, immediately release the gas. Reciprocating overheating Unlike factory engines, garden units are not designed to last long periods under full load in conditions of poor ventilation.
Use a heat-shrink tube on all electrical connections (ignition coil, stop button) to eliminate short circuit from water splashes.
The safety of passengers is also at risk due to the open rotating propeller. outboard motor nozzle It must be mounted so as to exclude contact of people with the propeller, and when maneuvering, mooring or landing people, the engine must be silenced or raised above water.
Maintenance and care of a homemade motor
After each release, the engine must be washed with fresh water, especially if the swim was in a salty pond, and the salt causes rapid corrosion of the aluminum alloys of the gearbox and steel elements. Trimmer. As a motor requires even more careful care than in garden conditions.
Check the condition of the shaft coils regularly, and if water enters the gearbox, it changes the color of the oil to emulsion (belevious), and if water is detected, the omentum and lubricant must be replaced immediately, otherwise the oil must be replaced immediately. bearing They'll be out of order, and the lubricant in the gearbox is changed every 10 to 15 hours.
Regular replacement of lubricant in the gearbox and checking the osteoils is the only way to extend the life of a homemade outboard motor based on a trimmer.
Store the device should be disassembled or with the fuel tank disconnected, in a dry room. Gasoline during long-term storage is oxidized and forms resins that clog the jelly carburetor. outboard motor nozzle It should be preserved for the winter period according to the instructions for the trimmer engine.
Advantages and disadvantages of using a trimmer
The main advantage of this design is that it's versatile and accessible. If you already have a powerful trimmer, the cost of upgrading is minimal. motorIt's easy to remove and use for its intended purpose, for mowing grass, and it's the perfect solution for the rare short-distance fishing trips.
The drawbacks are significant, however: the noise of the two-stroke engine is high, and vibration is transmitted to the entire hull of the boat, and the resource of the garden engine when operating at full speed (which is necessary for driving) is significantly reduced. Dry weight The design may also be larger than that of specialized electric motors of the same power.
⚠️ Attention: Don’t try to reach speeds above 10-12 km/h on such engines. The shaft and gearbox design is not designed for high speed modes and can collapse, leaving you without propulsion.
In the end, boat-motor It's an interesting technical experiment and a budget solution for leisurely travel, and for professional use or frequent travel, it's best to consider buying a specialized outboard motor that will ensure reliability and safety.
Can an electrotrimmer be used?
Theoretically, yes, but it requires a powerful battery and a sealed electric motor, which would have low efficiency because of transmission losses, and limited battery life.
Frequently Asked Questions (FAQ)
What is the minimum power trimmer for a boat?
To travel alone on a light boat (PVC), the minimum power must be 1.5-2 hp (about 33-40 cubic cm).
Should I change the oil in the trimmer engine when using it as a boat?
Yes, the intervals of oil change in the engine and especially in the gearbox should be reduced by half compared to the garden mode of operation, since the load on the unit is much higher.
Will a trimmer nozzle with a curved barbell fit?
No, it's not going to work. A curved bar involves a flexible cable that can't withstand the torque of the screw in the water and quickly fails, just a straight bar with a rigid shaft.
What speed can you develop with such a nozzle?
The real speed on calm water for a boat with one person will be about 5-8 km / h. This is the speed of a pedestrian, which is enough for fishing, but not enough for a quick move.