The idea of doubling the power of a power unit on a swimming vehicle is not new, and many aquatic motors, once they reach the limit of one engine, start thinking about a more radical upgrade. Spark outboard motors It is a technical solution that allows you to significantly increase the thrust and acceleration dynamics, but requires deep knowledge in the field of hydrodynamics and mechanics.
There's a common misconception that putting two engines automatically doubles the speed of the boat. It's not. In reality, the speed increase will be 10 to 15 percent, but the thrust and the ability to plane at full load will increase multiples. Tandem diagram Or a paired unit is the choice of those who value reliability and power reserve, not just top speed on an empty tank.
Before you start a project, you have to weigh the pros and cons. Installing a second engine is not just about buying another engine. It's about redesigning the transom, changing the weighting, reconfiguring the fuel system and, of course, the financial investments. In this article, we'll go into detail on how to implement the spark correctly, what schemes exist and what difficulties you will face.
The feasibility and physics of the Sparky process
The big question that the boat owner has is, why is it necessary? If your goal is purely speed, then buying one more powerful engine is often more profitable and technically competent. motor-spark It becomes justified.
The physics of the process says that water resistance increases exponentially. It takes a disproportionate amount of energy to increase speed by several knots. Two mid-range engines often run more economically than one motor squeezed to the limit of their capabilities. In addition, having two engines increases safety: if one fails, you can make it to shore on the other.
⚠️ Attention: If you don't do a good calculation of the differential, the boat can lose stability or become unmanageable at high speeds.
It's important to understand the difference between tandem (one by one) and parallel (two by one). Parallel circuit is a classic spark where both motors hang on a transom. Tandem circuit where the second motor is ahead of the first. The second circuit is difficult to operate and requires special shafts or elongated lower units, so it's almost not found in amateur shipbuilding.
Installation schemes: parallel and tandem
When designing a project, sparks often consider two main layout options: the choice depends on the design of the boat hull, the width of the transom and the owner's budget, each scheme has its own unique features of installation and operation.
Parallel is the most popular option, and two motors are attached to the same transom line or on a special platform, and it's critical to keep symmetry. lower unit If installed with a skew, the boat will be constantly led aside, which will require constant steering and increase fuel consumption.
- ✅ Advantages of the parallel scheme: ease of maintenance, uniform weight distribution, standard control system.
- ✅ The ability to use motors of different power (although this is not recommended for beginners).
- ❌ Difficulty with width: two motors take up a lot of space, which can interfere with the passage in the stern.
The tandem circuit (one motor in the kilvater of the other) is less common, and it keeps the width of the transom free and improves streamlinedness, but it requires a complex system of synchronization of the control of the rumples or the presence of an electronic control system (ESS), because physically pulling two tubes behind each other is impossible.
Technical nuances of tandem installation
In tandem installation, the rear motor operates in "discharged" water (aerated stream of the front motor), which reduces its efficiency by 10-15%, so the rear motor is often put more powerful than the front one.
Power calculation and selection of screw pairs
One of the biggest mistakes in sparking is the wrong screw selection, and if you use a single engine with a particular pitch, the flow geometry changes when you install two engines. Hydrodynamic resistance A pair of screws is different from the resistance of one.
Often, owners are faced with the fact that the boat does not get on plane or, conversely, the engines "twisted", this is a signal that the screw pitch is chosen incorrectly. Sparky often requires an increase in the pitch of the screw compared to a single installation to load the engines and reach optimal speed.
Let's look at the approximate ratio of the parameters for different types of boats, and the data here for reference, the exact calculation requires the weight of the crew and the cargo.
| Type of boat / Weight | Power of motors (2 pcs) | Recommended screw step | Expected speed gain |
|---|---|---|---|
| PVC 3.6 - 3.9 m | 2 x 9.9 hp | 11-12 inches | 5-7 km/h |
| Aluminum 4.5 - 5.0 m | 2 x 15-20 hp. | 13-14 inches | 8-10 km/h |
| Boat 5.5+ m | 2 x 40-60 hp. | 15-17 inches | 10-15 km/h |
A difference in pitch or diameter, even a half-inch, would cause one motor to overload and the other to idle, a direct route to overheating and breakage. gearbox.
Buy propellers from the same batch and from the same manufacturer, and even minor differences in blade geometry across brands can disrupt traction balancing.
Technical requirements for transom and fastening
The boat's tranny is the foundation of your power plant. The standard transom is often not designed to weigh two motors and the dynamic loads they create. The magnification of the transom is a must-have, and if you neglect that, there's a high risk of engine tearing off at full speed or cracking the hull.
Motor squashing is often done with a special motor bank or transompanes, which allows the motors to spread out wider, improve stability, and lower the mounting point lower, which has a positive effect on driving performance. AMg Or stainless steel.
Mounting motors should be made with a margin of safety. Bolts should be of a strength class not lower than 8.8, but preferably 10.9. The use of conventional construction bolts is unacceptable due to vibration loads.
☑️ Checking transance readiness for spark
Synchronization of control and fuel system
Controlling two motors is a separate topic to discuss: If you have rumpled motors, you'll either have to install a cable control system (like cars) or use electronic synchronization systems (ESS), pulling two tubes with one hand is physically difficult and uncomfortable.
If you use electronic control (gas/shifting cables or electric drive), you need to make sure that both motors respond to the movement of the handle at the same time. Dissynchronization will lead to yaw boats. Modern systems allow you to customize the sensitivity of each engine individually.
The fuel system also needs to be redesigned, you need two fuel tanks and a switching system or a dual fuel filter separator, and it's critical that both engines get fuel at the same pressure.
⚠️ Warning: Never connect the fuel hoses of two engines into a single tank without special valves, which can cause fuel to flow from one tank to another or create a vacuum in the system.
Fuel hose tees are often used to implement a reliable system, but it is better to install separate highways with the ability to switch, which will empty the tanks sequentially, keeping the boat balanced, or turn off one motor if necessary.
Perfect synchronization is achieved only when using a remote control system (D-box or analogue) even on engines with rompets.
Operation, maintenance and security
Operating a boat with a fleet of engines requires discipline from the owner, and now you need two engines to service, which doubles the time and money spent on fuel, candles and filters, but the reliability of such a system is worth it.
When driving, you need to constantly monitor the temperature of both engines. If one of the engines starts to warm, it must immediately shut down and continue to move on the second. The failure of one water pump (impeller) in the spark occurs more often due to possible blockage, so to carry spare impellers is the rule of good manners.
Spark maneuvering has its own peculiarities: at low speeds, the boat can be more prolific if you only gas with one engine to turn. At high speeds, on the contrary, the control becomes very clear, but any asymmetry in thrust (for example, an overgrown screw with grass) will be immediately noticeable.
- 🔧 Regularly check the tightening of the motor mount bolts - vibration from the two engines weakens the connections faster.
- 🔧 Keep an eye on the anodic protection status at both dayswoods.
- 🔧 Check the oil level in the gearboxes before each exit.
In conclusion, it is worth noting that boat-motor It's a journey for enthusiasts and professionals who lack standard solutions, and it's a journey that requires engineering, but gives you unique freedom to operate on the water.
Can I have two different engines of different power?
Technically possible, but not recommended, the motors will operate in different modes, resulting in desynchronization of traction, difficulty in driving and uneven wear, a difference in power of no more than 10-15%, provided that the screws are properly adjusted.
Will the fuel consumption increase significantly?
Yes, the combined consumption of two engines is always higher than one. However, if you run a boat at medium speed, you don't double the flow rate. Often two engines are 50 percent more efficient than one is 100 percent more efficient.
Do I need to register a second engine in the GIMS?
Yes, each engine with a capacity of more than 8 kW (about 10.88 hp) is subject to registration. If both engines are more powerful than this threshold, you must have documents for both, and the total power is taken into account when calculating the transport tax, if it applies in your area.
How does the spark affect handling in a storm?
Two motors provide better course stability. The boat is less susceptible to demolition by lateral wind and wave. However, the sailing of the structure (two dayswood) increases, which can create additional drift.