outboard motor bar under the trimmer: guide to selection and installation

Many owners of small boats, especially PVC boats or light aluminum models, often face the dilemma of buying a full-fledged mounted motor or limiting themselves to a trimmer. Using a gasoline or electric trimmer as the main propulsion is not only a way to save budget, but also the ability to significantly reduce the weight on the transom. However, to work effectively such a tandem, a reliable bar for the outboard motor under the trimmer, which will ensure the correct fit of the screw and stability of the entire structure.

Simply attaching a lower unit to a transom without a competent rod often leads to cavitation, loss of traction and, worst of all, damage to the lower unit due to air capture. A properly designed or matched sling leg allows the propeller to lower the waterline to an optimal distance, ensuring clean water flow. This is critical for acceleration and maneuvering, especially in shallow water or when the boat is fully loaded.

In this article, we will discuss in detail how such a bar works, what materials are best used in self-manufacturing and what to look for when buying a finished solution. You will learn about the nuances of centering, how to attach the datawood to the bar and methods of preventing vibrations that can destroy even the most durable structure in one season of active operation.

The principle of operation of the retractable bar for the trimmer

The main function of the remote bar is to change the geometry of the lower unit trimmer relative to the surface of the water. The standard trimmer leg is designed to work with fine diving, characteristic of working in grass or shallow water, where every centimeter of clearance is important. When mounted on a boat, this height is not enough, because the screw begins to grab air at the slightest heel or excitement, which causes cavitation And a sharp drop in efficiency.

The barbell is a lower unit extender that is rigidly fixed to the transom or a special bracket. Inside the barbell pipe, there is a shaft that connects the trimmer output shaft to the propeller. couplingThe structure must be sealed so that water does not get inside, but it must allow the shaft to rotate freely without backlashes.

Using such a system allows you to turn a regular garden tool into a full-fledged one. boat-engineThis allows for quick dismantling, so you can take off the trimmer in minutes if you need it and use it for its intended purpose, especially for tourists and fishermen who value the versatility of their equipment and don't want to carry extra pounds.

⚠️ Attention: When working with an elongated bar, the load on the trimmer gearbox increases. It is not recommended to use homemade structures longer than 1.5 meters on trimmers with a capacity of less than 2 hp, as this can lead to overheating and breakage. cross-plate.

The efficiency of the system depends on the quality of the assembly and balancing. If the shaft inside the bar is shifted relative to the center, there will be a beat that will quickly break the bearings. centre All the mating knots.

Materials and Construction: What to Choose

The choice of material for the barbell is the balance between strength, weight and corrosion resistance. aluminum-tube Aluminum is lighter, which is critical for inflatable boats, but it is more susceptible to mechanical damage when hitting rocks or logs. Stainless steel is heavier, but it guarantees durability even in an aggressive salty environment.

The interior shaft is usually made from stainless steel It is important that the shaft material and the pipe material do not create a galvanic pair in the presence of an electrolyte (water), otherwise electrochemical corrosion is inevitable. For insulation, plastic or textolite bushings are often used, which also act as slip bearings.

The trimmer attachment to the bar can be implemented in two main ways: through the transition flange or with the help of clamps. The flange connection is more reliable, since it eliminates the displacement of the deidvut under load, but requires accurate welding Clutters are easier to manufacture and allow you to adjust the height, but over time can weaken due to vibration.

⚠️ Attention: The use of conventional ferrous metal (St3 steel) for the submersible part of the bar is unacceptable without high-quality anti-corrosion coating. Even short-term damage to the paint will lead to rapid rusting and loss of sealing of the oal.

To seal the rotating shaft, we use coils or cuffs. Simple structures often use ready-made structures. slurry-knot They're not going to be able to get the right size of the shaft and the right size of the landing hole, so you can keep the water out of the trimmer gearbox.

Instructions for self-manufacturing

The process of creating a barbell yourself requires the presence of metalworking skills and a basic set of tools. First of all, you need to take the dimensions from your trimmer: the diameter of the datadvut, the distance from the mounting plane to the shaft exit, and the type of connection (slit or square), based on this data, you select the pipe of the desired diameter.

The next step is to make adapters, and the top adapter is attached to the trimmer's daydwout, the bottom one is attached to the screwdwin, and a coupling is placed between them to compensate for any distortions that may occur. squirt or locking screws which must be securely fixed against spontaneous unwinding.

The assembly is done in the following sequence: first, the bottom diewhint with a screw is installed, then the shaft inside the pipe is assembled, after which the pipe is sealed, the upper part is connected to the trimmer. After assembly, static leakage testing is performed, by immersing the assembled structure in a container of water and supplying air under low pressure.

The important thing is the lubrication. Inside the pipe, where the shaft passes, there must be a lubrication. lubricant (litol, solidol or special marine lubricant) that protects parts from corrosion and reduces friction, and the lubricant should be changed regularly, especially after heavy use.

⚠️ Warning: When welding aluminum structures, be sure to use argon welding. Conventional electric arc welding will not provide the necessary tightness and strength of the seam, which will lead to rapid destruction of the structure under the influence of vibration.

Installation and setup on the boat

Installation of the finished bar on the boat begins with the choice of the mounting site. pole-transom Or a platform that's attached to the balloon through a sling system, and metal boats allow you to weld a stationary bracket, which increases the rigidity of the entire system.

The height of the installation is controlled experimentally: the screw must be submerged in water to a depth of about half its diameter below the waterline when the boat is fully loaded; too deep a dive will increase the water resistance, and too small will lead to air sucking; Adjustment is done by moving the fasteners or changing the length of the suspension belts.

The inclination angle of the lower unit (different) also plays an important role. If the bow of the boat is raised too high when moving, the angle of inclination should be reduced. mounting Or the mounting point of the rod on the transom changes, and if you adjust the trim, you can get the boat to plane faster and save fuel.

After the initial installation, you need to do a test swim at minimum speeds, checking the system for vibration and heating. If all parameters are normal, you can gradually increase the speed by monitoring the behavior of the boat on the water. Remember to periodically check the tightening of the fasteners after the first hours of operation.

Capacity compatibility and specifications table

Not all trimmers work equally well in pairs with a retractable bar. Low-power models (less than 1 hp) may not cope with water resistance when using a long barbell, since some of the power is lost to friction of the shaft and overcoming the hydrodynamic resistance of the structure itself. engine-power.

For electric trimmers, the situation is even more critical because of limited battery capacity and peak engine power. The use of a heavy metal bar with an electric trimmer is only possible if the length is short and there is a screw with a small pitch. Gasoline engines are more tolerant to overload, but they also have their limits.

Below is a table showing the approximate ratio of the trimmer power and the recommended barbell parameters to achieve the optimal boat speed.

Trimmer power	Type of engine	Recommended length of barbell (max)	Rotor diameter	Expected speed (PVC 2-3 m)
0.5 - 0.8 kW	Electrical.	0.5 to 0.7 m	150-180 mm	3-5 km/h
1.0 - 1.5 hp	Gasoline 2T	0.8 - 1.0 m	180-200 mm	6-9 km/h
2.0 - 2.5 hp	Gasoline 2T/4T	1.0 - 1.2 m	200-220 mm	10-14 km/h
3.0 - 3.5bhp.	Gasoline 2T/4T	1.2. - 1.5 m	220-240 mm	15-18 km/h

When selecting components, pay attention to gear-rate Trimmer gearboxes: For boating purposes, it is often more profitable to use trimmers with more thrust-propelled gearboxes, even if their maximum speed is lower, which will make it more efficient to work with large diameter screws.

Typical errors and troubleshooting

One of the most common mistakes is to neglect balancing, and if the bar is skewed to one side, the boat will be constantly led away, and steering will become almost impossible without constant operator intervention. counterweight Or move the engine mounting point.

Another common problem is the lack of leakage of the gums, and the water that gets inside the daydvut is mixed with lubricant and turned into an emulsion that cannot protect the rubbing vapors, resulting in rapid wear and jamming of the gears and the shaft, and regular color checks of the lubricant (not white or milky) will help avoid costly repairs.

What if the screw is constantly catching air?

If the screw is constantly getting enough air, try placing an anti-cavitation plate made of aluminum sheet or plastic on the edge of the daywut, which should be placed horizontally above the screw and prevent air from being sucked out of the water surface, and check if the motor is too high relative to the transom.

Vibration is another enemy of reliability, and it comes from a screw imbalance, a shaft curvature, or a bad coupling, and prolonged vibration can unwind any bolts and destroy the plastic elements of the trimmer. vibroinsulators Check the balance of all the elements when you assemble.

FAQ: Frequently asked questions

Can I use a trimmer bar with an electric motor on seawater?

Use is possible, but requires careful protection. Electric motors often have aluminum housings that are prone to rapid corrosion in salt water. You need to use zinc anodes and regularly lubricate all connections. Also, make sure that the protection class of the electric motor is appropriate for immersion in salt water.

How much will the speed of the boat drop when using a homemade barbell compared to the factory engine?

Speed losses can range from 10 to 25 percent depending on the quality of the barbell, the length and the weight, and the main losses are spent on overcoming the resistance of the pipe itself and friction of the shaft, and a well-designed lightweight construction minimizes this effect, making it almost invisible at low power.

Should I change the oil in the trimmer gearbox when using with a retractable bar more often?

Yes, the intervals of oil change in the trimmer gearbox should be reduced by at least one and a half times. Working under constant load and at higher revs (compared to working in the grass) leads to faster aging of the lubricant.

Will this be suitable for a trimmer with a curved bar (flexible shaft)?

No, for flexible shaft trimmers (usually low-power models up to 1 hp), making a rigid retractable rod is impossible or extremely inefficient. The flexible shaft is not designed to work inside a long tube with support bearings and will quickly fail due to heat and friction.