Choosing an electric motor for an PVC inflatable boat is a costly problem: a weak engine will not pull the load, but a too powerful one will break the transom mount or quickly discharge the battery. nominal capacity in kilowatts (kW), and users are used to operating horsepower That's already confusing, but the big problem is deeper: The power of the engine must correspond not only to the weight of the boat, but also to the operating conditions. Current, excitement, number of passengers and even the type of battery.

In this article, we will discuss how precisely calculate the required power All things considered, avoid the typical mistakes of choice and save on fuel (or electricity) without losing performance. 1 hp engine can be more efficient than 3-horsepower In certain circumstances, and how to test it in practice.

Electric motors for PVC boats are divided into three categories by power:

  • 🔋 Weak (up to 0.5 kW / 0.7 hp) - for quiet water, solo fishing or short distance travel, suitable for boats up to 2.5 m long.
  • ⚡ Medium (0.5–2 kW / 0.7–2.7 hp) - universal option for boats 2.5-3.5 m with 1-2 passengers.
  • 💪 Powerful (over 2 kW / 2.7 hp) - for boats from 3.5 meters, high current or cargo transportation, requiring a reinforced transom and powerful batteries.

But this classification is just a starting point. The actual power requirement depends on the power of the system. specificityMany people make a critical mistake: they focus only on the data-sheet figures of the boat, ignoring the data of the boat. hydrodynamic resistance (which can increase the required power by 30 to 50 percent) and Efficiency of the screw (In low-cost models, it often doesn’t exceed 50%.)

Why the power of the electric motor is not equal to the speed of the boat

The most common myth: “The more powerful the motor, the faster the boat will go."In practice, the speed limit is not so much the engine as:

  • 🛶 Boat hull shape - PVC boats with inflatable keel (e.g., Bark 320K or Fregat M-330) have less resistance than flat-bottomed models.
  • 🌊 State of the water - on a wave or on a collision course, 2 kW can give the same speed as 0.8 kW on standing water.
  • 🔄 gear ratio motors with a high gear ratio (for example, Minn Kota Endura C2 55) develop a lower speed, but are better at low speeds.

The key parameter here is this. power-performance, which is the ratio of motor power to weight of a boat loaded. 20–40 W per 1 kg of total massFor example, for a boat weighing 100 kg with two passengers (80 kg each) and a load of 20 kg, the total weight will be 280 kg.

280 kg × 20 W/kg = 5.6 kW (7.5 hp) - but maximum value for severe conditionsThere's only 2-3 kW of standing water.

⚠️ Attention: Manufacturers often point out peak-power (e.g., "equivalent to 3 hp," which is only achieved for a few seconds. long-power It can be 1.5 to 2 times lower. Always check the power graphs for the time of operation in the engine data sheet.

Formula for calculating power: step-by-step instructions

To determine the required power, use the algorithm:

  1. Weigh the cargo boat:
    • Boat weight (indicated in passport, for example) Berkut 300 - 32 kg.
    • Weight of passengers (average - 80 kg per person).
    • Weight of cargo (equipment, batteries, fishing supplies).
  • Determine the resistance coefficient (K):
    • Standing water: K = 1.
    • Weak current (up to 1 m/s): K = 1,3.
    • Strong current (over 1 m/s) or wave: K = 1,5–2.
    • Calculate the minimum power (P) in watts: 
      P = (Total weight × K × 20 W/kg) / screw efficiency

      The efficiency of the screw for electric motors: 0.5-0.7 (take 0.6 for the average value).

    Example: boat Salut 330 (38 kg) + 2 passengers (160 kg) + 30 kg load = 228 kg. It is planned to operate on the river with a weak current (in Russian).K = 1,3Then:

    P = (228 × 1.3 × 20) / 0.6 ≈ 9780 W (9.8 kW or ~13 hp)

    But this is the result. overstated It takes into account the reserve to overcome the current. Minn Kota Riptide ST 80 (2.3 kW) if you don't require a record speed.

    Determined the total weight of the boat with cargo |

    Taken into account the resistance coefficient for its conditions

    Checked the real (not peak) power of the engine |

    Compared gear ratios of gearboxes across models |

    I made sure that the boat's mounting would withstand the chosen power.

    Table of power of electric motors for PVC boats

    For convenience, we have compiled power recommendations into a table that takes into account the length of the boat and typical operating conditions.Haswing Cayman, Watersnake T18, Torqeedo Travel 1003):

    Boat length, m Boat weight, kg Standing water Weak current Strong current/wave
    2,3–2,8 30 0.3–0.5 kW (0.4–0.7 hp) 0.5–0.8 kW (0.7–1 hp) 0.8–1.2 kW (1–1.6 hp)
    2,9–3,4 30–50 0.5–1 kW (0.7–1.3 hp) 1–1.5 kW (1.3–2 hp) 1.5–2.5 kW (2–3.3 hp)
    3,5–4,0 50–80 1–1.5 kW (1.3–2 hp) 1.5–2 kW (2–2.7 hp) 2.5–3.5 kW (3.3–4.7 hp)
    4,1–4,5 80–120 1.5–2 kW (2–2.7 hp) 2–3 kW (2.7–4 hp) 3.5–5 kW (4.7–6.7 hp)

    Please note: for boats with keel You can take 20 to 30 percent less power than that (due to less resistance). flat-bottomed (for example, Aqua 300NDL) - conversely, increase by 15-20%.

    Standing water bodies (lakes, ponds)|

    Rivers with weak currents |

    Fast-flowing rivers |

    Sea bays/coastal waters--

    The effect of the battery on the choice of engine power

    Electric motor and battery are systemThe weak link determines overall efficiency, even the most powerful motor.Torqeedo Cruise 4.04 kW) is useless if the battery can not provide the necessary current.

    • 🔋 Capacity (Ah) For example, for a 1 kW motor (current ~20 A), the 100 Ah battery will work. 100 Ah / 20 A = 5 hours at full capacity.
    • ⚡ Maximum discharge current A 2 kW (~40 A) motor requires a battery with a discharge current of at least 50 A.
    • 🔄 Type of battery:
      • Lead-acid (AGM/GEL) Cheap but heavy and afraid of deep discharge.
      • Lithium-iron-phosphate (LiFePO4) Light, durable, but expensive (e.g., Battery 12V 100Ah LiFePO4).

    A common mistake is to buy a motor with a power reserve "for the future" but without the battery. Haswing Osapian 55 1.2 kW with a 50 Ah battery will work just 50 Ah / 25 A ≈ 2 hours At full capacity, the weight of a lead battery of this capacity will be ~15 kg, which will eat up part of the boat's carrying capacity.

    ⚠️ Attention: Lithium-ion batteries (not LiFePO4!) are strongly discouraged for outboard motors due to the risk of high-current fire. Use only specialized marine batteries with vibration and moisture protection.
    💡

    If you're planning a long voyage, take two smaller batteries instead of one larger one, which will allow you to switch between them, extending your life, and making it easier to transport.

    The power of the motor: why can it be dangerous?

    The power of the motor directly affects the load on the boat-sweeper The plate to which the engine is attached. For PVC boats, the transom mount is usually designed to be loaded:

    • 🛥️ Up to 3.5 hp - standard transom (thickness 15-20 mm).
    • 🛥️ 3.5-10 hp - reinforced transom (25-30 mm) with additional stiffness ribs.
    • 🛥️ More than 10 hp - requires an aluminum or composite transom with a keel attachment.

    The problem is that many manufacturers of PVC boats claim the maximum power of the engine. non-dynamic loadingLike a boat. Honda Honwave T38 has a passport allowable power of 15 hp, but when installing the engine Mercury 9.9 (7.3 kW) on the wave transom can be deformed due to impacts on water. For electric motors, the risk is lower (no vibration like an internal combustion engine), but:

    • Motors over 3 kW require ferrot even for boats 3.5 m long.
    • In the case of big-step propeller The load on the transom increases by 20-30%.

    Check the transom mount of your boat: if it is made of thin plastic or has a backlash, the power of the motor should not exceed 1 hp for every 10 kg of boat weightFor example, for a boat weighing 50 kg, the maximum permissible engine is 5 hp (3.7 kW).

    How to check the transom for strength

    1. Install the motor and fasten it with standard screeds.

    2. sharply pull the motor up - if the trawler bent or cracks appeared on PVC, the mounting should be strengthened.

    3. Check the backlash: swing the engine left-right. The permissible backlash is no more than 2-3 mm.

    For motors above 2 kW, it is recommended to install an additional aluminum transax plate (thickness 4-6 mm).

    Top 5 mistakes when choosing an electric motor by power

    Even experienced water-engineers sometimes make mistakes when choosing an electric motor, and here are the most common mistakes and their consequences:

    1. Ignoring battery weight:

      When calculating the total weight, forget to add the weight of the battery (for example, a lead 100 Ah weighs ~30 kg), as a result, the engine is weak for real load.

    2. Buying a spare engine:

      A 5 kW motor for a 3.2 m boat is not a reserve. power-expenditureAt low speeds, the efficiency of the electric motor drops, and the battery goes down faster than at optimal load.

    3. Not counting the height of the transanth:

      Electric motors have a fixed length of lower unit (for example, 61 cm for a single engine). Watersnake ASP T24If the height of the transom of the boat does not match, the propeller will be too deep or shallowly immersed, which will reduce thrust by 30-50%.

    4. Savings on the screw:

      A standard 3-blade propeller is suitable for speed, but for traction (for example, when trolling) you need a 4-blade with a large pitch. The wrong propeller can eat up to 40% of the power.

    5. Neglect of tests:

      Even after the calculations, the engine may not live up to expectations. Always test it on water when the boat is fully loaded. Torqeedo Travel 503 on paper is suitable for a boat 3.5 m, but in practice can not pull against the current of 1.5 m / s.

    💡

    The optimal power of an electric motor is not the maximum, but the one that provides the desired speed at 60-80% load, which extends the life of the motor and battery by 30-40%.

    Comparison of electric motors and gasoline engines by power

    Many people switch from gasoline to electric, expecting the same power, but here's the catch: 1 hp electric motor is not equal to 1 hp gasolineThe difference is due to:

    • 🔌 Torque. Electric motors give the maximum moment from the first turns, while gasoline need promotion.
    • 🔄 Efficiency - electric motors it reaches 80-90%, gasoline - 20-30% (the rest is lost to heat and friction).
    • 📉 Power specifications - gasoline engines have a "peak" of power at high speeds, electric - uniform return.

    In practice, this means:

    • Electric motor Minn Kota Endura Max 55 (0.8 kW / 1.1 hp) in thrust comparable to gasoline Honda BF2.3 (2.3 hp) at low speeds.
    • To achieve a speed of 10-12 km / h on a boat 3.5 m will be enough electric motor 1.5-2 kW, while gasoline will need 3-5 hp.

    But there is also the flip side: electric motors lose in the maximum speed Because of the speed limits of the propeller, like the gasoline one. Yamaha 9.9 The boat will accelerate to 25-30 km / h, and electric Torqeedo Cruise 4.0 (4 kW) - only up to 15-18 km / h.

    Parameter 2 kW electric motor Petrol engine 5 hp.
    Speed on the boat 3.5 m, km / h 8–12 15–20
    Working time from full tank/battery 4-6 hours (100 Ah) 2-3 hours (5 liters of gasoline)
    Noise 50 db 70-85 dB
    Service No (except for the gearbox lubricant) Replacement of oil, candles, filters

    FAQ: Frequent questions about electric motor power

    Can I install an electric motor more powerful than the passport of a boat?

    Technically, yes, but it's fraught:

    • Damage to the transom (especially in boats with thin PVC).
    • Deterioration of handling due to excessive traction.
    • Quick battery discharge (the engine will not work in optimal mode).

    If you really need to increase the power, it is better. plough up with an aluminum plate and use a motor with smooth speed adjustment (for example, Haswing Protruder 2.0).

    Which motor to choose for trolling: 0.5 kW or 1 kW?

    For trolling (slow movement during fishing), it is not power that is important, but low-speedThe best choice:

    • 0.5 kW - for boats up to 3 m on standing water (for example, Watersnake T18).
    • 1 kW if you are fishing on a current or boat longer than 3 m (for example, Minn Kota Endura C2 55 with a 4-blade screw.

    Advice: Use a motor with a function Variable Speed (Smooth adjustment) – this will allow you to control the speed more accurately.

    How long will the 1 kW electric motor from the 100 Ah battery work?

    The working time depends on the load:

    • At full capacity (20-25 A): 100 Ah/25 A = 4 hours.
    • At 50% power (10-12 A): up to 8-10 hours.

    But remember, deep discharge reduces battery life, optimally discharge lead battery to 50%, LiFePO4 to 20%.

    Do I need to register an electric motor in GIMS?

    As of 2026 in Russia electric motors up to 8 kW (10.8 hp) The vessel is not subject to registration unless the boat is used for commercial purposes.

    • Motors over 8 kW are registered as small-boat.
    • Some water bodies (for example, in reserves) may have local power restrictions.

    Always clarify the rules on the site GIME Or at the local office.

    How to increase the speed of the boat without changing the engine?

    If the engine is weak, but you do not want to change it, try:

    • 🔄 Replace the screw on a model with a smaller pitch (thrust will increase, but the maximum speed will decrease).
    • 🛶 Reduce the weight of the boat For example, take a lighter battery (LiFePO4 instead of lead).
    • 🌊 Optimize streamliningRemove extra things from the sides, use a streamlined box for gear.
    • ⚡ Increase the tension (if the motor supports): for example, connect two 12V batteries in series to obtain 24V (increase power by 20-30%).