How much a outboard motor weighs is often a crucial question when buying a boat, especially if you plan to often pull it ashore or transport it on the roof of a car. Many beginners mistakenly focus solely on power, forgetting that the physical weight of the unit directly affects the differentiation of the boat and overall safety on the water. A heavy motor can require strengthening the transom, and too light will not be able to compensate for the weight of passengers in the bow.
The current market offers a wide range of solutions, from ultra-light electric tractors to powerful four-stroke giants that can weigh hundreds of kilograms. Understanding the difference in design and materials allows you to find the best balance between performance and ease of use. In this article, we will discuss all aspects that affect the weight of the engine in detail and help you make sure you do not make the wrong choice.
Factors affecting the total mass of the engine
The first thing to consider is the type of engine. Two-stroke engines It is traditionally lighter than its four-stroke counterparts of the same power, as they are simpler in design and do not require a complex lubrication system with a crankcase, but the difference in weight becomes less noticeable at low power and increases significantly with increasing cylinder volume.
The second important factor is the number of cylinders: a single-cylinder unit will always be lighter than a three-cylinder or four-cylinder unit of the same power, but the latter will provide a smoother run and lower vibration levels. yamaha and tohatsu Multi-cylinder circuits are often used even at medium power to reduce noise, which inevitably adds kilograms.
The third aspect is the electric starter system, and the battery pack adds 3 to 5 kilograms to the total weight, and although this seems small, when you carry it around often, every extra kilogram feels very strong.
- 🔧 Engine type: two-stroke or four-stroke cycle.
- ⚙️ Block design: number of cylinders and body material.
- 🔋 Additional systems: availability of an electric starter and generator.
⚠️ Note: The weight listed in the catalogs is often "dry" and does not take into account the weight of oil, fuel in the carburetor and lower unit, which in total can give an additional 2-3 kg.
When calculating the load capacity of the boat, always add at least 10% to the passport weight of the engine for unforeseen loads and attachments.
Weight categories of outboard motors
For ease of classification, all engines can be divided into several weight groups. Superlight engines (up to 10 kg) are typically up to 2 to 3 hp and are designed for small inflatable boats or as auxiliary engines, easy to operate with one hand, and transportation does not require powerful machinery.
The middle class (10 to 40 kg) covers a power range of 4 to 15 hp, the most popular category among anglers and recreational enthusiasts. Honda BF20 or Mercury 15They can already be equipped with a long-range lower unit series, which also affects the mass.
Heavy class begins where the weight exceeds 40-50 kg, there are powerful four-strokes and two-strokes with a volume of more than 40 cubic centimeters, Manual control of such units becomes difficult, and often requires the installation of a hydraulic lift or the use of a winch.
When choosing, it is worth remembering that The critical threshold for comfortable carrying by one person is considered to be 25-28 kilograms.Anything heavier requires either physical training or mechanization of the process of climbing the transom.
Comparative table: two-stroke vs. four-stroke
The difference in weight between the two main types of engines is due to design features: four-stroke engines have a gas distribution mechanism, an oil crankcase and often a more massive cylinder block. Two-strokes are lighter due to the absence of valves and the use of a mixture of oil and gasoline.
Below is a table showing the average weights for popular power classes, and the data is averaged by models from leading manufacturers, such as: Yamaha, Suzuki and Hidea.
| Power (hp) | Weight of two-stroke (kg) | Weight of four-stroke (kg) | Difference (%) |
|---|---|---|---|
| 2.5 - 3.5 | 9.5 - 10.5 | 12.0 - 13.0 | ~20% |
| 5.0 - 6.0 | 19.0 - 21.0 | 24.0 - 26.0 | ~25% |
| 9.8 - 10 | 26.0 - 28.0 | 34.0 - 36.0 | ~30% |
| 15 | 35.0 - 38.0 | 48.0 - 52.0 | ~35% |
As you can see from the data, as power increases, the weight gap increases. If for 5 hp the difference of 5 kilograms is not yet so noticeable, for a 15-horsepower engine, an additional 15 kg is already a serious argument against a four-stroke for owners of light PVC boats.
Why are 4-strokes heavier?
The four-stroke engine contains a full-fledged HRM mechanism (camshaft, valves, pushers), an oil pump and a crankcase designed for a large amount of oil. The two-stroke motor is structurally simpler: the mixture burns in a crank chamber, and the lubrication occurs directly in the working mixture, eliminating the need for heavy knots.
The influence of weight on the driving performance of the boat
Motor weight is not just a number in the passport, it is a factor in the behavior of the boat on the water. stern-sideIn this case, the bow of the boat is up, the visibility deteriorates, fuel consumption increases and the maximum speed decreases.
On the other hand, an overly lightweight engine on a heavy metal or composite boat will not allow for planing. The boat will dig a wave with its nose, choking and consuming huge amounts of fuel in transition mode. The balance of weight of the boat, passengers and engine should be perfect.
- 🌊 Otheriation: the correct weight distribution along the length of the body.
- 🚀 Gleaning: Minimum power and weight to enter mode.
- ⚓ Stability: The effect of weight on the roll of the boat when cornering.
⚠️ Warning: Installing a motor heavier than the boat recommended by the manufacturer can lead to the destruction of the transom and flooding of the boat at full speed.
The optimal weight of the engine allows the boat to go to plane at 2/3 of the maximum power, leaving a reserve for maneuver and movement against the current.
Transportation and installation: practical advice
If you plan to change outboard motors frequently or keep them separate from the boat, transportation is a big deal. Lightweight models up to 15 kg can be carried with one hand, holding a rample or a special handle. However, even 12 kg for 10 minutes cruising on rough terrain seems weighty.
For medium-duty motors (20-35 kg), it is strongly recommended to use wheeled wheel wheel bogies, which allow you to roll the engine directly to the transom. Installation of the motor on the transom requires a certain skill: you need to grab the motor behind the bumper (if it is rigid) and by the bracket of the lift, or use a winch.
☑️ Preparation for engine installation
When transported in a car, heavy motors should be placed only in an upright position or on a special side, so that oil does not get into the combustion chamber or air filter. Four-strokes are more demanding to be stored than two-stroke analogues.
How to safely lift a heavy motor by yourself?
There's a throw method, which is that the motor is placed between the legs, grabbed with two hands by the lower unit and the hummel, raised to the waistline, then turned and placed on the transom, but it requires good physical shape and is dangerous for the back, it's better to use mechanical assistants.
Hidden weight: what manufacturers are silent about
Often, customers are surprised to find that the actual weight of the engine differs from the stated in the catalogue. The fact is that manufacturers often indicate the weight without a lower unit (legs), without a screw and without oil.
Also worth considering is the weight of the screw. Aluminum screw is lightweight, but if you switch to stainless steel to improve driving performance, an additional 1-2 kg will be added. The remote control cable, if it comes complete, also has its own mass, which falls on the shoulders when carrying.
When choosing between brands, pay attention to the details: miccat often makes lighter housings, but heavier lower units, while tohatsu It is famous for its compactness and dense layout, which sometimes allows you to save a couple of kilograms on the overall length.
- 📏 lower unit: Standard or extended series (L, X, U).
- 🌀 Screw: The material and step affect the final mass.
- 🔗 Component: availability of cable, tools and Manuals.
So, when planning a boat's load capacity, always take the maximum possible weight. It's better to have a safety margin than to overload the boat. Remember, the water and fuel in the tank are also dynamic loads that add up to the weight of the motor.
Frequently Asked Questions (FAQ)
What is the maximum weight of the engine for an inflatable boat?
For most inflatable PVC boats with a length of 3-3.5 meters, the weight limit is 30-35 kg. Exceeding this value requires the presence of an inflatable keel and a hard transom, otherwise the feed will be immersed in water even in the parking lot.
How much heavier is a four-stroke two-stroke of the same power?
On average, a four-stroke engine is 20-30% heavier than a two-stroke analogue. For example, 9.9 hp in two strokes weighs about 27 kg, and in four strokes - already about 36-38 kg.
Does the length of a lower unit affect the weight of the engine?
The switch from standard lower unit (S) to long (L) adds 3 to 5 kg to the total engine weight due to the lengthening of the lower unit pipe and intermediate shaft.
Can I put a more powerful, but lighter, engine on an old boat?
You can, if the transom can withstand the load on the break, but you need to watch for differentiation. Too light and powerful motor can lift the nose of the boat, which is dangerous on the wave, often requires moving batteries and passengers closer to the nose.