Choosing a power unit for a boat is always about finding a compromise between speed, battery life and budget, unlike gasoline, where horsepower is the main indicator. power It's often measured in pounds of thrust, which at first confuses many water-engineers, and understanding the physics of the process avoids buying a device that's too weak to pull the boat off the plane, or an overly powerful one that will drain the battery in an hour.
The efficiency of electric traction directly depends on the voltage of the onboard network and the quality of the screw group. Minn Kota. and watersnake They use different labeling systems, but the physics remains the same: the higher the efficiency of the system, the less energy is lost to heat and more goes into useful motion. It is important to bear in mind that the specifications declared by the manufacturer are often peak values, achievable only under ideal laboratory conditions.
In this article, we will discuss how to interpret the specifications correctly so that your fishing does not turn into a fight against the current or the wind. The real speed of the boat at full load can differ from the passport by 15-20% in a smaller way.So, the power supply is never superfluous, and the smart calculation will allow you to enjoy the silence of the electric current without worrying about the sudden discharge of the battery in the middle of the reservoir.
Fundamental Concepts: Traction vs Power
The main misconception of beginners is to try to convert horsepower directly into pounds of traction. Electric motor traction (Thrust) is the static force with which a propeller pushes water when a boat is stationary. It's not the same as the power that is used to create this propulsion. For electric motors, the de facto standard has become a measure in pounds (lbs), where 1 lb of thrust is approximately 0.45 kg of force.
The power consumption is expressed in watts and depends on the voltage of the system (12, 24 or 36 volts) and the current strength. Power (W) = Voltage (B) × Current (A)And that's what you do with how fast your battery goes down, and high thrust at low voltage requires huge currents, which leads to heating of the wires and loss of energy.
Why pounds?
The use of pounds of traction has historically been in the United States, where the trolling motor industry was born, a convenient unit for measuring the static force that the propeller develops. Translating into the usual kilograms of force helps us better imagine how much weight can move the motor from its place, although the hydrodynamic resistance of the body is more important for driving in water.
Modern models are equipped with control systems that optimize energy consumption. i-Pilot Or similar autopilot systems allow the motor to operate in the most economical modes, maintaining a given speed rather than constant revolutions, which significantly affects the real range.
Traction is the push force, and power is the battery's energy consumption rate, and for long walks, the efficiency of the system is more important than maximum traction.
Calculation of the necessary thrust for different types of boats
To determine which motor you want, you need to start from the displacement of the boat. There is a rule of thumb: for every 30-50 kg of total weight of the boat (hull + motors + equipment + people), 1 pound of thrust is required. However, this rule works for calm water and low speeds. If you plan to go against the wind or current, the reserve ratio should be increased.
PVC inflatable boats have high water resistance due to soft cylinders deformed under load. resistance Metal or plastic flat-bottomed boats (Kazanki) require less thrust to enter mode, but more energy to maintain high speed due to the large area of contact with water.
Consider the approximate table of correspondence of the weight of the boat and the required thrust of the engine:
| Boat type / Weight with cargo (kg) | Recommended traction (lbs) | System voltage (B) | Expected speed (km/h) |
|---|---|---|---|
| Inflatable PVC (up to 400 kg) | 30-40 lbs | 12 | 5-7 |
| Metal / Plastic (up to 700 kg) | 50-60 lbs | 12/24 | 7-9 |
| Boat with flat bottom (up to 1000 kg) | 70-80 lbs | 24 | 8-10 |
| Heavy boat / anchorage | 100+ lbs | 36 | 10-12 |
The choice should also be considered the availability of additional equipment. sonars, lighting devices and pumps also consume energy from the same battery, which reduces the time of the engine. It is always better to take a model with a thrust reserve of 20-30%, so as not to operate the engine to the limit of its capabilities.
Effect of on-board network voltage on efficiency
Going from 12 to 24 or 36 volts is not just a marketing ploy, but a physical necessity for powerful systems. As the voltage increases, the current required to get the same power decreases proportionally. Less current means less heating of the wires, terminals and controller, and less battery loss.
Most modern medium-power motors are transphasic, meaning that the same motor can run from 12, 24 or 36 volts depending on how the batteries are connected. 12V You're using a single battery, in mode. 24V two, connected in series, and in mode 36V The serial connection adds the voltage, leaving the capacitance (Ah) unchanged.
⚠️ Attention: When batteries are connected in series to produce 24 or 36 volts, it is critical to use batteries of the same capacity, age and preferably of the same brand. Unbalanced cans will cause one battery to discharge faster than another, which can cause deep discharge and failure of the entire ligament.
Higher voltages allow for smaller wires, which make installation easier and reduces tackle weight, and powerful motor controllers (80 lbs and above) are often designed for 24 or 36 volts, as 12 volts of currents reach 100 Amps and higher, requiring very expensive and heavy switching.
The screw group and its impact on efficiency
The screw is the last element in the energy conversion chain, and it determines how efficiently the shaft will turn into the movement of the boat. The propeller blades have a complex profile, and their geometry (step, diameter, number of blades) is tailored to specific tasks. Standard screws are designed to balance speed and thrust.
Electric motors are characterized by the use of screws with a larger diameter and a smaller pitch compared to gasoline counterparts, which is because electric motors give out maximum torque immediately, without the need to gain momentum. Efficiency of the screw It can range from 50% to 70% depending on the cleanliness of the surface and compliance with the operating mode.
- 🌀 Two-bladed screws: Usually provide higher speeds, but may be noisier and prone to cavitation at high revs.
- 🌀 Three-bladed screws: The middle ground for most tasks, provide smooth running and good traction at medium speeds.
- 🌀 Five-past screws: They create maximum traction at low revs, ideal for trolling and movement in overgrown algae places, but limit the maximum speed.
Regularly check the screw for coiled lines or hair. Even a small bundle of hair on the shaft can significantly reduce efficiency and lead to overheating of the osteoils.
Damage to the edges of the blades, even microscopic, disrupts the laminar flow of water, creating vortices. This not only reduces speed, but also creates additional noise that can scare off fish. For fishing, it is recommended to use rounded-edge screws, which are less prone to chipping when in contact with the bottom.
Autonomous life and battery capacity
Motor power dictates the requirements for battery capacity. Electric motors are not suitable for starter car batteries, which are designed to give a short-term strong pulse.
Capacity is measured in Ampere-hours (Ah). A simple calculation shows that a motor consuming 20 Amps at an average speed will discharge a 100 Ah battery in about 5 hours (given that lead-acid batteries are not recommended to discharge more than 50-60%). Lithium-iron-phosphate (LI-Phosphate)LiFePO4) batteries allow up to 80-90% of the capacity to be used without harming the resource.
Factors that reduce working hours:
- ❄️ Low temperature: In winter or cold water, lead battery capacity can drop by 30-40%.
- 🌬️ Wind and current: Movement against the elements requires the operation of the motor at high speeds, where the current consumption is maximum.
- 🌿 Overgrowth: Movement through the algae increases the load on the shaft and motor, increasing the current consumption.
☑️ Checking the power system before exit
Common mistakes in selection and operation
One of the most common mistakes is to buy a sideways engine in terms of power, and many water-engines focus on the minimum weight of a boat in the dry state, forgetting about the full crew, equipment, fuel and water in the hold, and as a result, the engine runs at its limit, quickly draining the battery and overheating.
The other extreme is the installation of a too powerful engine on a light inflatable boat without a transom plate. Cavitation In this case, it can be so strong that the propeller will start to capture air, and the boat will start to burrow its nose or become uncontrollable instead of accelerating.
⚠️ Warning: Never turn on the motor unless the propeller is fully submerged in water. Drying even for a few seconds can damage the osteoils and cause windings to overheat, as the water serves as the main cooler in the lower part of the lower unit.
Also worth mentioning is the mistake of ignoring the state of the electrical wiring: using thin wires or wires with oxidized contacts leads to a drop in voltage at the terminals of the motor. The motor tries to compensate for the lack of voltage by increasing current, which leads to even more heating and loss of power. Use only copper wires with the section recommended by the manufacturer.
How to extend the life of the battery using a powerful motor?
To extend battery life, try not to drain lead acid batteries below 50%, and gel and AGM batteries below 60%. After each fishing, immediately put the battery on charge. If you use the motor at maximum thrust constantly, consider increasing the capacity of the battery bank or switching to lithium technologies that have higher efficiency and lower weight.
Can I use an electric motor as the main one?
Using an electric motor as a main motor on a strong current is possible, but requires careful calculation. You need a thrust reserve of at least 50% of the design and a battery of increased capacity. On a fast current, the boat experiences tremendous resistance, and the engine will operate at maximum power, which will quickly deplete the standard battery.
What if the engine is humming but the boat is not floating?
If the motor makes sound but there is no traction, check the propeller: it can be wound with grass or a line, it can also damage the veneer (if any) or cut the shaft. In rare cases, the problem may be the cliff of the anchor winding, but most often it is a mechanical obstacle or cavitation due to improper scoring.