Choosing a power plant for small boats is often a difficult dilemma for owners of inflatable boats and boats, there are many solutions on the market, but a special place is occupied by units that are popularly called “trimmer”, although technically these are outboard motors with manual trim control or a specific design of the lower unit, understanding their device is necessary for proper operation and prevention of breakdowns.
Unlike stationary engines, these outboard They are attached directly to the trunk of the boat and can be removed at any time, giving the owner the freedom to maneuver and the ability to quickly replace the failed unit or simply to lighten the boat during transportation, the principle of operation is based on the transfer of torque from the crankshaft through the vertical shaft to the propeller.
And you'll have to pay special attention to the cooling system, which is most often off-shore, and the water is sucked in through the holes in the bottom of the lower unit and circulates around the cylinders, and you're going to use the boat in shallow water, and it's important to be aware of the risk of overheating, because you're going to have to be able to use the boat in shallow water. water-intake They can capture air or sand.
⚠️ Warning: Starting the engine out of the water, even for a few seconds, is guaranteed to cause the pump coils to fail and the piston group to overheat. Always check the control jet before starting.
Constructively, modern models are divided into two-stroke and four-stroke, and this choice determines not only fuel consumption, but also weight and noise level. Two-stroke units are easier and easier to maintain, while four-stroke units are more economical and environmentally friendly. For small boats, PVC engine weight is often the deciding factor in choosing.
Structural features and device of lower unit
The basis of any outboard motor is a lower unit that goes into water, and inside it is a shaft that transmits rotation from the engine to the propeller, and at the bottom there is a gearbox that changes rotation by 90 degrees. gearsThey are experiencing enormous loads when working at high speeds.
The most important safety feature is the emergency screw drop system, which cuts the pin or turns the mechanism when it hits an underwater obstacle, preventing the engine shaft from breaking down. crankshaft Some modern models are equipped with friction clutches that do not require replacement of pins.
Gas and gear shifting can be controlled remotely or via a humming wheel. tiller models are popular among anglers because of their compactness and simplicity. gaskle and the cable control.
Why does it make lower unit long?
The length of a lower unit has a direct impact on the efficiency of a propeller. The deeper the propeller is, the less it captures cavitation bubbles from the surface of the water, which is especially important when a boat is excited or fully loaded.
- 🔧 gearbox A unit requiring regular oil change, usually once a season or after 100 hours.
- ⚓ Anti-cavitation plate - protects the screw from air capture and improves the thrust specifications.
- 🌊 pomp - the heart of the cooling system, the rubber impeller which wears out from sand and dirt.
Materials used in manufacturing also play a key role: Aluminum alloys are lighter but susceptible to electrochemical corrosion in salt water; stainless steel and special coatings protect critical components but increase the overall weight of the structure; the choice of material depends on the operating conditions: aluminum will suit freshwater bodies, more resistant alloys for the sea.
Advantages and disadvantages of hanging units
The main advantage of the suspension circuit is modularity, so if the engine fails, the boat does not turn into a useless piece of rubber on the shore, the unit can be taken to the service, and in its place temporarily install another. small-boat.
But it also has its downsides: the outboard motor creates a moment on the transom, which can lead to a full tank differtation and one passenger. hydrofoilThey are installed on an anti-cavitation plate.
⚠️ Attention: Incorrectly mounting the engine in height can lead to cavitation of the propeller or, conversely, to an increase in water resistance. Optimal height - when the anti-cavitation plate is 1-2 cm below the flat bottom of the boat.
Noise and vibration are another aspect that often bothers owners: Four-stroke models are quieter, but two-stroke models are better at acceleration dynamics. Modern noise-muffling technologies reduce acoustic discomfort, but it is difficult to completely eliminate it on small boats due to the resonance of the hull.
The cost of ownership also varies: Two-stroke engines require a mixture of gasoline and oil, which is an inconvenience for some users; four-stroke engines need regular replacement of engine oil and filters, which increases the list of consumables required, but their resource before major repairs is usually higher.
Comparative table: Two-stroke vs. Four-stroke
When choosing a power plant, the question often arises: what type of engine should you prefer? To structure the information and make it easier to make a decision, we have prepared a comparative analysis of the main specifications, which will help you weigh the pros and cons before buying.
| Characterization | Two-stroke engine | Four-stroke engine |
|---|---|---|
| Weight. | Lighter (no oil crankcase and valves) | Heavyer (complex construction of GBC) |
| Fuel consumption | Above (part of the mixture goes into the exhaust) | Below (savings up to 30-40%) |
| Noise level | Tall, sharp sound | Low, flat hum |
| Service | Simple but frequent (candles, mixture) | More difficult but less frequent (oil change, filters) |
| Price. | Cheaper to buy. | Costly to buy. |
As you can see from the table, the choices are based on priorities. If you care about every kilogram of weight and you like simplicity, a two-stroke is perfect. If you value comfort, silence, and long transitions, a four-stroke unit will pay off its cost with fuel savings.
Also worth considering is the liquidity of the equipment. Tohatsu, Yamaha or HondaThey're easier to sell in the secondary market, and their parts are available, and the design is familiar to service center craftsmen, and exotic or new Chinese brands can create repair problems in remote areas.
Installation and initial start rules
Mounting the motor on a transom is a procedure that requires precision and safety. Incorrect tightening of the rods can cause the engine to fall into water during movement, which can lead to loss of the unit and damage to the screw. Use only regular fasteners and check their condition before each foray.
Before the first start, you need to check the oil level in the gearbox and, in the case of a four-stroke motor, in the crankcase of the engine. Often new units are supplied without oil, and starting on dry will be fatal. fuel-mix It is prepared in the correct proportions (usually 1:50 for modern oils).
☑️ Check before the first launch
The start-up process usually starts with pumping the fuel manually until the pear feels firm, and then we move the gear knob to neutral. NFor a cold engine, we close the suction valve (if it is mechanical) and sharply pull the starter, and after warming up, we open the suction and let the engine work at idle speeds.
It's important to control the body temperature. If the motor overheats, immediately turn it off and check the cooling system. Often the problem is a clogged water intake or damage to the impeller pump. Regular prevention prolongs life. cooling-system It prevents expensive repairs.
Maintenance and maintenance of the motor
Regular maintenance is the key to the long service of your trimmer assistant, the main attention should be paid to changing the oil in the gearbox, it is recommended to do this at least once a year, before winter storage. The oil should be transparent; if it has acquired the color "coffee with milk", then water through the glands has entered the gearbox.
Lubrication of the friction nodes is also mandatory. Control cables, pivot joints and metal contact points require a consistent lubrication. This prevents movable parts from acidifying, especially after being operated in salt water. Corrosion is the main enemy of any mechanism that comes into contact with water.
After each saltwater fishing, be sure to rinse the engine with fresh water outside. Leave it to run at idle speeds in freshwater tanks or simply pour the off-board holes with a hose to flush the salt from the cooling system.
Ignition plugs require inspection and cleaning every 50-100 hours; the load on the electrodes indicates engine malfunction or poor fuel; the color of the electrode should be brick-brown; black plaque indicates a rich mixture, and white indicates poor or overheating.
⚠️ Warning: When you can preserve for the winter, be sure to drain the fuel from the carburetor or use a stabilizer. The remaining gasoline evaporates, leaving a resinous plaque that clogs the jellyfish and makes starting in the spring impossible.
Typical malfunctions and methods of their elimination
Even the most reliable boat-engine One of the most common problems is that there's no spark, and first of all, check the candle: unscrew it, press it against the mass, pull the starter. If there's no spark, check the ignition coil and the stop button.
The second common problem is poor fuel delivery: a dirty sludge filter, a squeezed hose or a clogged carburetor jet launderer can stop the engine, often by simply purging the system or replacing the fuel filter, which is an expendable material.
Knocking at the bottom of the motor or vibration may indicate damage to the propeller or a foreign object hitting the gearbox. In such cases, you should immediately stop and conduct a visual inspection of the lower unit. Ignoring foreign sounds can lead to the destruction of gear gears gear gears.
90 percent of the problems with starting old engines are related to the fuel system (old gasoline, dirt in the carburetor) or the ignition system (candles, tips).
Frequently Asked Questions (FAQ)
Can a four-stroke engine be fueled with a mixture of gasoline and oil?
No, absolutely not. In a four-stroke engine, the oil is in the crankcase and lubricates the rubbing parts separately from the fuel, and pouring the mixture into the tank will cause the engine to fail quickly, coking the rings and releasing oil into the exhaust system.
What is the best octane number of gasoline to use?
Most modern engines are designed for gasoline AI-92 or AI-95The use of fuel with a lower octane number can cause detonation and destruction of the piston group.
Why does the engine stop at idle speed?
There may be several reasons: a contaminated idle jettison of the carburetor, air sucking through the gasket, improper adjustment of the screw quality of the mixture or a malfunction of the ignition system. It is also worth checking whether the idle channel in lower unit is clogged.
Do I need to run a new engine?
Yes, break-in is mandatory. During the first 10 hours (or fuel tanks), you can't give full load. It's usually recommended to run at speeds up to 50-60% of the maximum, and this is necessary for the burn-in of the rubbing surfaces of the piston group and bearings.