Choosing the right powertrain for an inflatable vessel is not just a matter of buying the most powerful engine you can afford, it is a complex engineering trade-off between weight, cockpit dimensions, bottom design and desired speed. A miscalculation can cause the boat to scour the course, choke on the wave, or, worse, deform the transom at the most inopportune moment.
In this article, we will discuss the key parameters that affect the selection boat-engineThe right boat-motor bundle will not only provide a comfortable walk, but also economical fuel consumption, and will also prolong the life of your boat.
The first thing to start with is to carefully study the technical documentation that comes with your boat, where the manufacturer gives the maximum allowable power and recommendations for crew weight, and ignoring this data often leads to loss of warranty and the creation of accidents on the water.
Analysis of the specifications of the boat and transpant
The basis for the choice is the design of the boat itself, namely the type of bottom and the quality of the transom. low-pressure inflatable floor (LDPB) They have excellent seaworthiness, but require more careful handling of powerful engines due to the peculiarities of load distribution. The rigid solder bottom (plywood or aluminum) creates a more stable platform, allowing you to reach high speeds without risking damage to the structure.
The tranx is a critical node that senses all the thrust of the engine, can be rigid or removable. In the case of a removable transom, it is important to make sure that it is securely fixed and has no backlash. The loaded transom is a guaranteed vibration that will quickly destroy not only the mountings of the motor, but also the mounting itself. lower unit engine.
⚠️ Attention: Never install a motor above the engine specified in the boat's passport, and exceeding the limit can lead to the rupture of cylinders or the tearing off of the transom at full speed, which is deadly.
Plywood transverses, even laminated ones, can be layered over time from constant contact with water and vibration. Aluminum inserts or fully aluminum transverses are less common, but they are much more reliable when used with powerful power plants. two-stroke or four-stroke engines.
Power calculation: 2 hp vs. 10 hp and more
The main question that the owner faces is: what power to choose? There's a rule of "middle ground." Too weak engine will not lead the boat to the boat. gellingIt's going to be a waste of power, and it's going to be too powerful to overload the structure and make the control dangerous.
For small boats up to 3 meters long with an inflatable floor, a motor with a capacity of 2-3.5 hp is often enough. Such units weigh about 10 kg and allow you to comfortably move together at a speed of 10-12 km / h. However, they are not designed to go into plane with full load.
If your goal is high-speed cruising and fishing at long distances, you will need power from 5 hp and above. boats with a length of 3.2-3.6 meters with a hard bottom confidently plane with engines 9.9-15 hp It is important to consider that with increasing power, the weight of the engine increases, which is critical for inflatable boats.
For boats with a length of 3.2-3.6 meters, the optimal choice is often a 9.9 hp engine with the possibility of stretching up to 15 hp This gives a power reserve and saves fuel when cruising quietly.
When calculating power, you also need to consider the number of people and equipment. If you plan to walk alone, you can save on power. For family exits with a load of gear, tents and anchors, a power reserve is mandatory.
Two-stroke or four-stroke: the choice of engine type
The eternal confrontation of the two types of engines is especially important for owners of PVC boats. Two-stroke engines (2T) is traditionally lighter than its four-stroke counterparts of the same power, a key factor, as every extra kilogram on the transom of an inflatable boat has a significant impact on the differentiation and handling.
Four-stroke (4T) motors are quieter, more economical and more environmentally friendly. They don't require a fuel mix, which makes life easier for the fisherman. However, their weight often becomes an obstacle. For example, a four-stroke 5 hp can weigh as much as a two-stroke 9.9 hp.
| Parameter | Two-stroke (2T) | Four-stroke (4T) |
|---|---|---|
| Weight. | Easy, 20-30%. | Harder, harder to carry |
| Fuel consumption | Higher, need a mix. | Down 20 to 30 percent, clean gasoline. |
| Noise | High, sharp sound. | Low, flat hum |
| Transportation | You can put it on your side. | Only vertically (or oil drain) |
For PVC boats, which often have to be carried by hand to the water or lowered from the sloping shore, the weight of the engine often becomes the decisive argument in favor of a two-stroke. If you have a ladder or walk from an organized parking lot where the engine can be left on the boat, the 4T will be more comfortable.
The myth of "butter consumption"
Modern two-stroke engines with E-TEC or similar technologies inject oil dosed, which reduces its consumption and smoke almost to the level of four-strokes, while maintaining low weight.
The influence of boat length on motor choice
The length of the hull is the main limiter. For boats up to 2.8 meters long, using motors more powerful than 5-6 hp often makes no sense, even harmful. Short base does not allow you to effectively plane with a heavy motor on the transom, the boat begins to peck with its nose or, conversely, pushes it too high.
The optimal range for engines 9.9-15 hp begins with a length of 3.2 meters. Boats size 3.6-4.0 meters are already considered full-fledged high-speed boats capable of carrying motors with a capacity of 20-30 hp and more, but here already raises the question of the strength of cylinders and transom.
As the boat length increases, the surface area increases, requiring more thrust to enter the plane, but a long boat with a low-powered engine will simply sail slowly, consuming fuel inefficiently.
⚠️ Attention: When installing a heavy motor on a short boat (less than 3 meters), be sure to check the trim. you may have to move the seats or load forward to compensate for the weight of the engine on the transom.
Rule of conformity: for every 30-40 kg of total weight of the boat (with crew and cargo) in the planing mode should account for about 1 hp of engine power.
Motor weight and its impact on driving performance
The weight of the power unit for an inflatable boat is not just a number in your passport, it's a factor that determines your back when you go down and how you behave on the go. A heavy motor causes the stern to sink deeper, increasing the resistance of the water.
To compensate for the weight of a heavy 4T engine, owners often use the engine. sink-tank It's a fuel-based solution, and it's a bow-based solution that helps to level the gap, but it adds to the complexity of handling and takes up useful space in the cockpit.
There are special models of motors with shortened lower unit or lightweight cylinder block, created specifically for small inflatable vessels, which allow you to get the desired power without a critical stern advantage.
- 🎣 Lightweight motors (up to 12 kg) are ideal for fishing alone and frequent carry-on.
- ⚓ Average weight (12-20 kg) requires careful balancing of the boat or the help of a partner.
- 🚀 Heavy motors (more than 25 kg) on PVC boats require mandatory check of the strength of the transom and the presence of assistants.
Transport and installation of the engine
Installing the motor on a transom is a procedure that requires attention to detail. The motor must be strictly centered. A skew even a few degrees will lead to the boat drifting aside and uneven wear of the lower unit. Use robust rods, preferably with rubber pads, to keep the transom coloring intact.
The most important parameter of the installation is the height of the suspension. If the anti-cavitation plate is too high, the screw will grab air on the turns. If it is too low, the water resistance will increase. Optimally, the plate is 1-2 cm below the bottom of the boat.
☑️ Check before the first launch
When transporting in a car, it is better to remove the engine if possible. Constant vibration and jerks when driving on the roads can damage the lower unit or mounts. If you can not remove the engine, be sure to use the transom wheel drive to relieve the load from the cylinders and transom.
⚠️ Attention: Always use a safety rope (sturt), run through a special ring on the tiller or engine body and fixed on the boat, this will save the engine from loss in the event of its falling overboard.
Frequently Asked Questions (FAQ)
Can I put a motor more powerful than the boat's passport allows?
Theoretically, it can, but it's dangerous and illegal. Excessive power leads to overloading of trans and cylinders on the wave. In the event of an emergency, the insurance company will refuse payment, and GIMS can write a fine for violation of the rules of operation of small craft.
Which motor is better for fishing: 2T or 4T?
For trolling and long standing at a point, 4T is better because of the silence and economy. For quick transitions between points and if ease of carrying is important, modern 2T is better.
Do I need to develop a new engine before the first trip?
It is usually 10 hours or 2 tanks of fuel, during which you can not give a full load (more than 70-80% of the gas) to the engine parts to rub together.
Why doesn't the boat go out on plane with a powerful engine?
There may be several reasons: improper installation of the engine in height, overloading the boat (too many people or cargo in the stern), blunt or damaged screw, or overgrown lower unit algae.