Choosing the right engine for a sailing or purely cruising catamaran is not just about buying equipment, but finding the balance between speed, weight and efficiency.
Unlike monochulous vessels, catamarans have a specific hydrodynamics, where excess power can lead to inefficient fuel consumption, and its lack - to the impossibility of going to plane or overcome a strong current.
Many beginners make the mistake of focusing only on passport power, forgetting about the length of the lower unit and the weight of the unit itself, which is critical for inflatable or collapsible structures.
In this article, we will discuss all the nuances that will help you make an informed decision and enjoy safe navigation.
Key parameters of engine selection
The first and most important criterion is engineIt must strictly conform to the specifications of your inflatable or rigid design.
Catamaran manufacturers always indicate the maximum permissible power on the transom, and exceeding this value can lead to the destruction of cylinders or a fracture of the transom board.
However, it is important to consider and real-time If you are planning long expeditions with a lot of equipment, it makes sense to take a motor with a small margin of thrust.
⚠️ Warning: Installing a motor that is too powerful on a light catamaran can lead to yaw and loss of controllability at high speeds, which is dangerous in narrowness.
The second critical parameter is lower unitIt is short (S), long (L) and ultra-long (XL).
Catamarans often require a long lower unit, as the distance from the transom to the water they have more than conventional boats, and a short motor will constantly capture air, losing traction.
Gasoline vs. electric motors
The debate over which engine type is best has been going on for years, and the choice depends solely on your tasks and operating conditions.
Gasoline two-stroke Traditionally popular due to its low weight and high specific power, which is ideal for light inflatable catamarans.
They are easier to transport, as they are not afraid of slopes, but require preparation of the fuel mixture and make more noise.
Modern. four-stroke It is quieter, more economical and more environmentally friendly, but their weight can be critical for small craft, requiring careful balancing.
Electric motors are gaining popularity for quiet fishing or cruising in protected areas where noise is prohibited.
Their main disadvantage is the limited working time and the need to carry heavy batteries, which on a catamaran with limited carrying capacity becomes a serious problem.
- 🚤 Gasoline: high autonomy, refueling anywhere, high speed.
- ⚡ Electricity: no exhaust gases, silence, minimal vibration, but low speed.
- 🔋 Hybrids: the possibility of using solar charging in parking lots to replenish energy.
⚠️ Warning: When using an electric motor, be sure to take into account the weight of the batteries, as their placement on the nose or stern can disrupt the catamaran's differentiation.
Features of installation on the catamaran transom
Installation of the engine on the catamaran requires a special approach to the organization of the transom assembly, since standard solutions from PVC boats are often not suitable.
You'll need it. cross-board, which must be rigidly fixed between cylinders or on the frame to withstand the emphasis of the screw without deflection.
Often a system of two boards is used, clamping cylinders, which allows you to adjust the height of the suspension of the motor.
It is important to ensure that strub-fixationSince the vibration of two-cylinder motors can gradually weaken the puff.
☑️ Checking the engine installation
For safety, it is recommended to use an additional safety falter, which will prevent the loss of the engine in the event of an unexpected slip.
The height of the anti-cavitation plate installation should be selected experimentally: too deep immersion will increase resistance, and too high will lead to cavitation.
Comparative table of popular models
To simplify the choice, we have prepared a comparison of the specifications of popular engines, which are often installed on catamarans of different tonnage.
Pay attention not only to horsepower, but also to weight, as for portable catamarans, every kilogram counts.
| Model | Power (hp) | Weight (kg) | Type | Recommended size of catamaran |
|---|---|---|---|---|
| Tohatsu M5BDS | 5 | 25.0 | four-stroke | Up to 3.5 meters |
| Yamaha 2CMHS | 2.5 | 12.5 | two-stroke | Up to 3.0 meters. |
| HDX T 9.8 BMS | 9.8 | 26.0 | two-stroke | 4.0 - 5.0 meters |
| HDX F 15 BMS | 15 | 35.0 | four-stroke | Over 5.0 meters. |
| Nissan Marine NS 9.8B | 9.8 | 25.5 | two-stroke | 4.0 - 5.0 meters |
When choosing a specific model, always check with maximum power specified in your catamaran passportThis is a safety requirement, not a recommendation.
Heavyer four-stroke engines may require reinforcement of the transom part or redistribution of the load to the bow of the vessel.
Operation and maintenance of the motor on water
The aquatic environment is aggressive, especially if you walk on salty water bodies or polluted industrial rivers.
Regular cooling-wash fresh water after each exit is a mandatory procedure that prolongs the life of the pump and the cooling shirt.
Catamarans are characterized by higher clearance, which increases the risk of screw strikes against floating objects or the bottom in shallow water.
What do you do when you're screwed?
If you feel a blow, immediately turn off the gas and turn off the engine. Examine the screw for cracks and check if the fishing line has wound on the lower unit, which may damage the glands.
Always carry a set of spare candles and splints for the rumpell checks, as the vibration on the catamaran is higher than on keel boats.
Keep an eye on the condition. transom-weed: if the motor starts to pick up the nose at full speed, it may be necessary to install a hydrofoil or adjust the angle of inclination.
⚠️ Warning: Never leave the motor in the water for a long time unnecessarily, especially in the fouling water, this will lead to corrosion and overgrown algae.
Safety and management of the catamaran
Control of the catamaran with the engine has its own specifications due to the wide body and sailing.
In the case of side winds, the boat can be very heavy, so maneuvering It requires early start of turns and inertia.
Always use. tether (check), tying it to a life jacket so that in the event of a person falling overboard, the engine automatically deafens.
The distribution of crew weight also affects handling: shifting people to one side can improve or worsen course stability depending on the situation.
Frequent mistakes in choosing and buying
One of the most common mistakes is to buy an engine "for growth" without taking into account the actual carrying capacity of the vessel.
People often forget that loading capacity The catamaran includes the weight of passengers, equipment, the engine itself and fuel.
If you buy a heavy 15-horsepower motor for a small catamaran, you may simply not have the buoyancy margin to safely get out on the water with a full tank.
Fuel quality is also often ignored: modern engines are sensitive to octane and water in gasoline.
Choosing the right motor is a compromise between the desired speed and the actual carrying capacity of your catamaran.
Buying a used engine without a compression diagnosis and a spark check can turn into expensive repairs in the first season.
Always check the availability of documents and the correspondence of the number on the lower unit to the number in the documents to avoid problems with registration in the GIMS.
Can the engine be more powerful than the manufacturer recommends?
Excessive power leads to overloading of the transom board, destruction of the cylinder anchorages and loss of stability of the vessel at speed, which can cause rollover.
Which screw is better to choose for loaded catamarans?
For heavy, full-load catamarans, reduced-stroke propellers are better suited to provide better acceleration and traction, although the top speed may decrease slightly, but the motor will not run in overload mode.
Do I need to register a catamaran with a motor?
Yes, according to the rules of GIMS, any boats with an engine power of more than 3.68 kW (5 hp) are subject to mandatory registration, regardless of the length of the hull.
How to store the engine in winter?
You need to completely drain water from the cooling system, develop the residues of fuel from the carburetor or preserve it, remove the battery and store the engine in a dry room in an upright position.