The choice of an electric motor for an inflatable vessel often becomes a complex puzzle, where physical quantities, specifications and financial constraints are intertwined. Unlike gasoline analogues, where horsepower and cylinder volume are the main criterion, in the world of electric traction, the Newton meters, amperes and volts rule. Beginners often make the mistake of buying an over-thrust device, which leads to a rapid discharge of the battery, or, conversely, acquire a weak engine that can not bring the boat to plane even alone.
The main task in the selection of equipment is to find the middle ground between the weight of the vessel, the desired speed of movement and autonomy of the course. Electric motor traction (measured in pounds or kilograms) is the force pushing your boat, not your top speed. Understanding this difference is critical to saving your budget and enjoying fishing or cruising. In this article, we'll explore the physics of the process, calculation methods, and nuances that will help you avoid the typical mistakes in boat configuration.
Before we move on to the numbers, you need to realize that electric traction works in a completely different mode than the internal combustion engine. There is no flywheel inertia and torque in the usual sense, but there is an instantaneous return and a direct dependence of the current consumed on the load on the screw. Trolling engine It should be selected so that when the boat is fully loaded, it does not work at the limit of its capabilities, but in the optimal efficiency range.
Fundamental concepts: traction, power and voltage
The first step to making a smart choice is to avoid comparing electric motors to gasoline motors in horsepower. Electricians use the concept of thrust, which is measured in pounds (lbs). One pound of thrust is approximately 0.45 kg of force. However, a dry figure of thrust without reference to system voltage and current consumption does not give a complete picture of the energy efficiency of the device.
Onboard network voltage Most low-power motors (up to 30-40 lbs) run from 12 volts; more powerful units designed for heavy boats often require 24 or even 36 volts; switching to higher voltages reduces the current in the circuit at the same power, which reduces loss in wires and heating of components.
⚠️ Attention: Never try to connect a 12-volt motor to a 24-volt battery or assembly. An instantaneous power surge will cause the stator windings to burn and the electronics to fail without any recovery capability.
It is also worth mentioning efficiency of the efficiency (COP)Two motors with the same declared thrust may consume different amounts of energy, and a more expensive motor with a better winding and rotor geometry is often more profitable to operate, since it travels a longer distance on a single battery charge.
When buying an engine, pay attention to the length of the lower unit. For inflatable boats, the standard length (about 70-80 cm) is often excessive, which creates unnecessary resistance, but too short a shaft will lead to the capture of air by a screw on the wave.
Method of calculation of necessary thrust for PVC boat
There is a simple but effective formula for determining the minimum thrust required, based on the total displacement, that is, the sum of the weight of the boat itself, the engine, the battery, passengers, equipment and water reserve in the tanks (for a gasoline-powered engine), it is generally assumed that for a comfortable movement into the calm, thrust is approximately 10% of the total weight.
However, for a confident run against the wind or current, as well as to enter a mode close to planing (if the design of the boat allows), the power reserve must be significantly higher. Optimal ratio It's 20 to 25 percent of the total mass, and if you're planning to actively fish in large bodies of water, where the wind blows often, you'd better focus on the upper end of that range.
Consider an example: the weight of a PVC boat 30 kg, an engine 8 kg, a battery 20 kg, a fisherman with a tackle 100 kg. Total: 158 kg. Minimum traction (10%) - 16 kg (35 lbs. Comfortable traction (25%) - 40 kg (88 lbs. Based on this, the engine with a thrust 30-40 lbs (13-18 kg) will work at the limit, and the engine 50-55 lbs (22-25 kg) will ensure a confident run.
It is important to understand that hull PVC boats also make adjustments: Boats with inflatable floor (BBB) have more water resistance than models with a floorboard hard bottom. For the former, the power reserve should be increased by 15-20% compared to the latter with the same load weight.
Table of correspondence of boat weight and engine power
To quickly understand the market, you can use a summary table that shows the approximate match between the thrust of the electric motor, maximum load and expected speed, and the data is relevant for standard operating conditions in calm.
| Motor traction (lbs) | Traction (kg force) | Max. load weight (kg) | Typical speed (km/h) | Recommended voltage |
|---|---|---|---|---|
| 30-34 | 13-15 | 500 | 5-7 | 12 V |
| 40-45 | 18-20 | 700 | 7-9 | 12 V |
| 50-55 | 22-25 | 900 | 9-11 | 12 V |
| 60-70 | 27-32 | 1200 | 11-13 | 12/24 In |
| 80+ (Twin) | 36+ | until 1600 | 14-16 | 24/36 V |
It's worth noting that the speed shown in the table is the theoretical maximum for ideal conditions, and in practice, if there's a wave or a wind, the speed will decrease and the energy consumption will increase. Twin-engine systems Twins not only allow you to double the thrust, but also to implement differential control, which significantly improves maneuverability.
When choosing a motor from the upper range of the table, make sure that the transom of your PVC boat will withstand the weight of such a unit and the stress it creates. Reinforced transom boards are a prerequisite for installing powerful electric tractors.
Selection of battery: capacity and type
The power of the motor is useless without the appropriate energy source. If a gasoline engine requires a tank of fuel, the electric one eats an ampere watch. This is where the law of conservation of energy comes into force: the more powerful the motor you choose, the more capacious the battery must be to keep the battery running.
The market is dominated by two types of batteries: lead-acid (AGM/GEL) and lithium-iron-phosphate (LiFePO4). The former are cheaper but heavier and dislike deep discharge. The latter are 2-3 times lighter, can discharge almost to zero without loss of life, but are much more expensive. lithium batteries It's becoming a de facto standard.
☑️ Checking the readiness of the ACB for the season
The capacity is calculated from the average current of consumption. If the motor consumes 40A at maximum speed, then a 100Ah battery theoretically would provide 2.5 hours of running. However, given the losses and the ban on full discharge of lead batteries, the real supply will be about 1.5 hours. For a full fishing day (6-8 hours), the total battery capacity should be at least 200 Ah with a moderate driving style.
⚠️ Attention: Do not use car starter batteries to power electric motors. They are designed for short-term return of huge current and quickly degrade with prolonged discharge with low currents, which can lead to the boiling of the electrolyte and explosion in the confined space of the boat.
The Influence of Screw and lower unit Design on Efficiency
What many people overlook is that the propeller itself is a power converter. Electric motors on PVC boats are critical to the pitch of the propeller. Small pitch propellers provide better traction at low revs, which is ideal for trolling. Large pitch propellers allow for high speed but require more power and can choke on full load.
The screw material also plays a role. Plastic screws are cheap and safe (will not damage the leg or bottom on contact), but they are less hydrodynamically efficient and can be deformed. Metal screws (aluminum, stainless steel) provide better returns but require installation cut-off or friction couplings to protect the motor from impacts on underwater obstacles.
lower unit (motor foot) must be submerged to optimum depth. Diving too shallow will lead to cavitation and loss of traction, and diving too deep will lead to increased water resistance and reduced speed. Adjusting the depth of immersion is a delicate process that depends on loading the boat.
The Secrets of Setup lower unit
The optimal depth of the propeller is when the axis of the propeller is 10-15 cm below the waterline when the boat is fully loaded. If the propeller creates a funnel on the surface, it must be dug up.
Typical errors in configuration and operation
One of the most common mistakes is to buy a motor with a margin without considering the capabilities of the battery: the owner puts a powerful motor at 55 lbs, but leaves the old battery at 60 Ah. As a result, the engine does not reveal the potential, and the battery dies in an hour, creating the illusion of inefficiency of the train as a whole.
The second mistake is to ignore the state of the chargers, and the cheap chargers may not recharge the battery or, conversely, recharge it, reducing life. smart chargers with a multi-stage algorithm (Bulk, Absorption, Float) is necessary to maintain the health of the battery.
Contact protection is also often overlooked. In salt water or just high humidity, oxidation of the terminals causes voltage to drop and the connections to heat up. Regularly lubricating the contacts with special compounds and using copper tips is a simple but vital procedure.
A balanced system “Motor + battery + screw” is always more effective than just a powerful motor in conjunction with a weak battery.
Frequently Asked Questions (FAQ)
Can an electric motor bring the PVC boat to plane?
Theoretically, yes, if the boat is light, with a hard bottom and a flat transom, and the engine is powerful enough (80 lbs and above), but for most classic PVC boats, the electric motor is used for quiet movement, trolling or maneuvering, since the plane mode quickly lands the battery.
How much battery power is enough for 100 AH?
At the minimum speed (trolling 3-4 km/h), this battery will last for 6-8 hours; at the maximum speed (full gas), the operating time will be reduced to 1-1.5 hours; the average mode will allow you to travel about 15-20 km.
Do I need to register a boat with an electric motor in GIMS?
Under current Russian legislation (at the time of writing), registration is required for small vessels with an engine capacity of more than 8 kW (about 10.8 hp). Electric motors are much weaker than this threshold (usually up to 1-2 kW), so registration is not required if the total weight of the equipped vessel does not exceed 200 kg.
Can I charge the LiFePO4 battery with a conventional battery charger for acid batteries?
Charge algorithms for lithium and lead differ in cut-off voltage and stages. Charging lithium with a lead charger can lead to undercharging (loss of capacity) or, in the worst case, damage to the BMS (control board) of the battery.