Idea to use lawnmower In practice, thousands of water-powered boats across Russia have already tried this budget-friendly way of equipping a PVC boat or aluminum boat with a homemade engine, based on the conversion of a gasoline trimmer (or motokos) into an outboard outboard motor - cheaper than buying a new one. Yamaha or MercuryBut with a lot of nuances.

The main plus of this decision is The cost of a homemade engine is 5-10 times lower than the factory analogue with a capacity of 2-5 hp. For example, a trimmer. Husqvarna 128R (2 hp) costs about 15,000., while the new one Honda BF2.3 But the downside is that homemade structures require precise balancing, water protection, and proper attachment to the transom, and mistakes are not only fraught with breakdown of equipment, but also with danger on the water.

In this article, we will analyze what trimmers are suitable for reworking, how to make a nozzle yourself (with drawings and photos), which ones are suitable for reworking. risk It's important to consider what kind of off-the-shelf solutions are already on the market, and also the real testimonials of those who have been swimming in these engines for a long time.

What trimmers are suitable for conversion into a outboard motor

Not every gasoline trimmer can be adapted for a boat.

  • 🔧 Power: optimally 1.5-3 hp (trimmers weaker than 1 hp will not pull even an inflatable boat, more powerful 3 hp - excessive and dangerous without the correct gearbox).
  • 💧 Water protection: the engine must have a sealed air filter and ignition system protection, ideally if the model is initially positioned as "all-weather".
  • ⚙️ Type of gearbox: straight shaft (without curves) simplifies the design of the nozzle. Models with a curved shaft will require an additional adapter.
  • ⛽ Fuel.Two-stroke engines (a mixture of gasoline and oil) are easier to rework than four-stroke engines, but less economical.

Among the tested models:

  • 🔹 Husqvarna 128R (2 hp) - reliable Swedish engine, popular among homemade manufacturers.
  • 🔹 STIHL FS 55 (1.1 hp) - light, but weak for boats longer than 3 m.
  • 🔹 Patriot PT 3355 (1.8 hp) - budget version with direct transmission.
  • 🔹 Echo SRM-22GES (0.9 hp) - only for ultralight boats (up to 200 kg).

Important: Chinese no-name trimmers (for example, Forte>, Champion) often have weak bearings and plastic gears in the gearbox, they quickly fail when loaded on water. Husqvarna or STIHL Avito.

📊 What trimmer do you plan to use for the boat?
Husqvarna
STIHL
Patriot
Echo
Another (write in the comments)
I haven't decided.

Design of the nozzle: what is needed for remodeling

A homemade nozzle on a trimmer for a boat consists of several key elements:

  1. Fixing to the transom A metal plate or bracket that holds the trimmer upright, can be made of 5-6 mm thick aluminum or can be made with prefabricated attachments from older outboard motors.
  2. Row-rotor gearbox The most complex node.
    • 🔄 Remove the regular trimmer gearbox (suitable for models with a straight shaft).
    • 🛠️ Use a gearbox from a Bulgarian or drill (lathe processing is required).
    • 💰 Buy ready-made squirt for self-made motors (for example, from WaterMotor).
  • The propeller - optimal diameter 180-220 mm (for trimmers 1.5-3 hp). You can take from the old outboard motor or order aluminum on AliExpress.
  • Cooling system Options: water pump (as in factory engines) or forced fan blowing.
  • Control handle It's a gas and clutch lever that's mounted on a transom, so you can adapt a bicycle handle or use a regular trimmer handle.

    • Tools will be required for manufacturing:

    • 🔨 Bulgarian and welding machine (if you make the bracket yourself).
    • 🔧 A set of keys and screwdrivers for disassembling the trimmer.
    • 📏 A rod for accurate measurements of the shaft and gears.
    • 🖌️ Metal paint (for protection against corrosion).
    What happens if you don't balance the screw?

    An imbalanced propeller creates a vibration that is transmitted to the trimmer shaft.

    (1) Accelerated wear of gear bearings (life is reduced by 3-5 times).

    (2) Risk of failure of the motor attachment to the transom (especially if it is homemade).

    (3) Loss of speed due to uneven thrust.

    (4) Discomfort in driving - the boat can "talk" from side to side.

    Step-by-step instructions for the manufacture of the nozzle

    Let’s look at the process by the example of a trimmer. Husqvarna 128R (2 hp) and a homemade gear reducer from urala.

    Pour gasoline and oil | Remove the regular coil with the line | Disconnect the barbell from the engine | Check the integrity of the shaft coils | Clean the air filter from dust-->

    Step 1: Disassembly and modification of the trimmer

    Remove the trimmer bar with a gearbox. In most models, it is attached to 2-4 bolts. Carefully remove the shaft - it will have to be shortened or replaced with a stronger one (for example, from a more durable one). STIHL).

    Remove the standard gearbox, which is not suitable for working in water. Instead, install a transition coupling (can be grinded on a lathe or ordered from a master), the clutch must connect the trimmer shaft to the shaft of a homemade gearbox.

    Step 2: Manufacture of the gearbox

    For the gearbox suitable gears from the motorcycle ural or Minsk (transfer ratio 2:1 or 3:1) The body can be made of an aluminum block or welded from steel plates 4-5 mm thick.

    Assemblage pattern:

    1. Set the lead gear on the trimmer shaft.
    2. Fix the driven gear on the intermediate shaft (it should go beyond the gearbox body and connect to the propeller).
    3. Close the body, having previously missed the joints with a sealant (for example, ABRO 11-AB).
    4. Drill the hole for lubrication (use it). Litol-24 or Shrus-4).

    Step 3: Installation of the propeller

    The screw is attached to the gearbox shaft through a veneer or a cone adapter.

    • 🔹 The screw must rotate. clockwise If you look at the boat, then the boat will be “leading away”.
    • 🔹 The propeller blades should not touch the gearbox body - a gap of at least 5 mm.
    • 🔹 To protect against cavitation, cover the blades with epoxy resin.

    Step 4: Fastening to the transom

    The bracket can be made from an aluminum corner of 40×40 mm.

    1. Weld to the corner plate for fastening the engine (with holes under the bolts of the trimmer).
    2. On the other side of the corner, fasten the plate for fixation to the transom (with rubber pads for cushioning).
    3. Install adjusting bolts to change the angle of inclination of the motor (the optimal angle of immersion of the screw is 5-10 °).

    Paint the finished structure. hammer-paint It's a corrosion protection.

    💡

    Before the first start on water, check the balance of the screw on land: press the shaft into the drill and spin up to 2000 rpm. If the vibration is strong, sweat the blades or add a counterweight.

    Ready-made nozzles: a review of factory solutions

    If you don't want to mess around with homemades, you can buy a trimmer nozzle ready, and there are several proven options on the market:

    Model Type Trimmer power Price (2026) Features
    WaterMotor WM-1 Reductor + screw 1.5-2.5 hp 12 000 ₽ Aluminum case, water cooling, screw 3 blades
    Motorboat ML-1 Complete set 2-3 hp. 18 000 ₽ Includes mounting, gearbox, screw and gas handle
    BoatMotor DIY Assembly kit 1-2 hp. 8 500 ₽ Requires turning gears, no screw.
    AquaMotor Profi premium gearbox up to 5 hp 25 000 ₽ Stainless body, SKF bearings, stainless steel screw

    The advantages of ready-made nozzles:

    • ✅ No need to look for details and turner.
    • ✅ Warranty (most manufacturers have 6-12 months).
    • ✅ Optimized propeller geometry for low-power engines.

    Cons:

    • ❌ The price is comparable to the cost of a used factory engine (for example, Tohatsu 3.5 You can find it at 25,000 )..
    • ❌ Not all nozzles are suitable for trimmers with a curved shaft.
    💡

    Ready-made nozzles are profitable if you do not have access to a lathe or experience with metal, otherwise the homemade option will cost 2-3 times less.

    5 Critical Mistakes and How to Avoid Them

    Homemade trimmer boats are a source of increased danger.

    ⚠️ Attention! Never use a trimmer with plastic-reducer When loaded, the gears crumble and the fragments can damage the screw or get into the water, posing a danger to swimming.

    Top 5 Beginner Mistakes:

    1. Lack of protection against rolloverIf the boat flips over, the trimmer will continue to operate underwater, which is a direct route to hydraulic shock and engine failure. float-off (costs 300-500 ).).
    2. Incorrect angle of inclination of the motorIf the propeller is too deep, resistance increases, if fine, the boat will "slug." Optimally, the top edge of the propeller is 2-3 cm below the keel.
    3. Lack of coolingThe trimmer engine overheats in 10 to 15 minutes of continuous operation, and the minimum solution is to blow a fan, better a water pump.
    4. Weak transom attachmentHomemade thin metal brackets bend at wave. Use aluminum at least 5 mm thick or 3 to 4 mm steel.
    5. Use of an unsealed fuel tankGasoline can leak into the boat, which is a fire hazard. Replace the regular trimmer tank with a sealed one (for example, from a tank that is not a tank that is airtight). Mercury).

    Additional security measures:

    • 🔹 Always have on board. fire extinguisher (even on a small boat).
    • 🔹 Check the screw attachment before each outing.
    • 🔹 Do not exceed the speed of 10-12 km / h - homemade engines are not designed for high loads.
    ⚠️ Attention! Trimmers with line-fill (for example, STIHL FS 38) are not suitable for boats, and the feeding mechanism may jam under load, leading to a shaft break.

    Speed and load capacity: what to expect from a homemade engine

    The actual performance of a trimmer outboard motor depends on three factors: engine power, boat weight and propeller geometry.

    Trimmer power Boat length Max. weight (passengers + cargo) Speed (calm water)
    1-1.5 hp 2.8 m 150 kg 5-7 km/h
    1.8-2 hp 3.5 m 250 kg 8-10 km/h
    2.5-3 hp 3.5-4 m 350 kg 10–12 km/h

    Important nuances:

    • 🔹 During the current or wave speed drops by 20-30%.
    • 🔹 Aluminum boats are heavier than PVC - they need a power reserve.
    • 🔹 The three-bladed propeller gives more traction, but requires a more powerful engine.

    Example of the practice: boat Frigate 320 (3.2 m, PVC) with a motor of Husqvarna 128R (2 hp) and a homemade 200 mm propeller shows 9 km / h with one passenger. When loading 200 kg (2 people + tackle), the speed drops to 6-7 km / h.

    💡

    To increase the speed by 10-15%, you can set transmolator It reduces the turbulence of the water behind the screw.

    Owner reviews: pros and cons in practice

    We interviewed owners of homemade outboard motors from trimmers in VKontakte groups (in Russian).Boat-makers, Russian water-enginesHere are the typical reviews:

    👍 Andrey, Moscow: "Using." Patriot PT 3355 nozzle WaterMotor season two. Flying winger 3 It's 8 or 9 km/h, enough for trolling, just to keep an eye on the engine temperature, and I stop for 5 minutes per hour to cool it off.

    👎 Igor, Krasnoyarsk: "Make the engine out of STIHL FS 55 It's weak for my boat (3.6m) and it's barely crawling for two, so I had to buy a battery trolling engine to help.

    👍 Dmitri, Peter: "Remove." Husqvarna 128R I'm not going to have a problem with a Bulgarian gearbox in a season. foul-coating - less sticking grass.""

    General conclusions from the reviews:

    • ✅ Pros: Low price, ease of repair, possibility of modernization.
    • ❌ Cons: Noisy, vibrating, requires constant temperature control.

    The average lifetime of a homemade motor is 2-3 seasons with careful operation.

    1. Water in the engine (30% of cases)
    2. Wear of gear bearings (25%).
    3. Breakage of the screw when hitting an obstacle (20%).

    FAQ: Frequent questions about lawnmower nozzles for boat

    Can I use an electric trimmer for a boat?

    Technically possible, but impracticalElectrical trimmers (e.g., Makita UR3000) have a power of up to 1 hp and run on the battery for 10-15 minutes. The boat will require an external battery 12V 100Ah, which adds weight and cost.

    Which screw is better: 2 or 3 blades?

    Depends on the task:

    • 🔹 2 blades It's faster, but less thrust, and it's good for light boats in calm water.
    • 🔹 3 blades - Better thrust at low speeds, but higher resistance, optimal for trolling or load boats.

    For trimmers 1.5-2 hp, 3-blade screws with a diameter of 180-200 mm are more often used.

    Do I need to register a homemade motor in GIMS?

    I agree. Order of the Ministry of Emergency Situations No. 447 of 2020, power-driven motors up to 3.68 kW (5 hp) The GIMS inspector may require the engine documents (checks, trimmer passport) to be produced, but in practice, problems are rare, but it is better to carry a copy of the trimmer passport.

    How to increase the life of a homemade motor?

    5 tips from experienced boaters:

    1. Change the oil in the gearbox every 10 hours (use it) Lukoil TM-5 85W-90).
    2. After each trip, wash the screw and gearbox with fresh water.
    3. Install. net-filter Water intake (protection from grass).
    4. Keep the engine in a dry place, before draining gasoline.
    5. Check once a season. gear-gap (should be 3-5 mm).

    Can I use a trimmer nozzle for a boat?

    For a boat or hard boat with a length of >4 m homemade trimmer motor wrongReasons:

    • 🔹 Insufficient power (needs at least 5-10 hp to get on plane).
    • 🔹 High risk of shaft failure due to increased load.
    • 🔹 The lack of a reverse makes maneuvering more difficult.

    Exception - aluminum boats up to 4 m with a flat bottom (for example, Kazankah-5M), but it is better to use the factory engine here.