Comparison Tohatsu M5BDS vs Mercury 5M

The highest shaft speed that the outboard motor is capable of developing.

Theoretically, the speed of rotation of the propeller (or turbine — see "Motor type") depends on the engine speed, and, accordingly, the speed that the boat is capable of developing. However, in addition to this indicator, many other factors also affect the performance of the motor — engine power (see above), gear ratio (see below), propeller design, etc. As a result, situations are quite normal when a more powerful and high-speed motor has lower revolutions than the weaker one. Therefore, this parameter is, in fact, a reference one, and has almost no practical value when choosing. Unless it can be noted that high-speed motors are more susceptible to noise and vibration than low-speed ones; however, this moment can be compensated by the use of various technical tricks.

The design of the exhaust system in a gasoline outboard motor (see “Engine type”), more precisely, the method of exhaust gases used in this system.

— Above the screw. This category includes two types of engines. The simplest option is when exhaust gases are emitted directly into the air. Such systems are extremely simple and cheap, but the exhaust can create a noticeable inconvenience for people in the boat (not only because of the gases, but also because of the rather high noise level); therefore, they are found only in the simplest outboard motors, and even then quite rarely. A more common option is to release exhaust gases into the water above the propeller (most often through the so-called anti-cavitation plate — a flat ledge above the propeller). Such systems are more comfortable than "air" ones, while they are simpler and cheaper than propeller exhaust (see below), although they are still considered less technically advanced.

— Through the screw. In systems of this type, the exhaust is led into the water directly through the propeller hub; in fact, the position of the exhaust pipe coincides with the axis of rotation. This reduces the noise level compared to systems using exhaust over the propeller, and also slightly increases power and traction characteristics. The downside of these advantages is the design complexity and, accordingly, the high cost.

Possibility to use a petrol engine generator(see "Engine type") to power an external load.

The generator is an indispensable element in the design of any petrol engine — it is responsible for creating the spark necessary for ignition. However, not every outboard motor has the ability to power an external load from this generator — therefore, if such an opportunity is important to you, you should choose a model where it is directly stated. And the generator system can come in handy, first of all, if you plan to use additional equipment on the boat — power from the generator is in a number of ways more convenient than from autonomous batteries, and it is for it that many navigation systems, echolocation, radio communications and other instruments and equipment are made . In addition, if necessary, devices outside the boat can also be powered from the generator — for example, a starting charger for a car.

The supply voltage supplied by the generator system installed in the outboard motor.

Almost all such systems work with a voltage of 12 V — this is a standard widely used in modern automotive and water technology, it is under it that the electrical systems of the engines themselves, and electronic devices for cars and boats are made. There are practically no exceptions to this rule.

The highest current that the generator system installed in the outboard engine is capable of delivering (see above). The characteristics of the load that can be connected to the generator depend on this indicator: its total current consumption should not be higher than the maximum current of the generator, otherwise the latter will work with overload, which is fraught with malfunctions and even accidents. Also, this information is useful if you plan to use the generator to charge batteries (car or boat): each battery has its own charging current, and the power source must match them.

The total volume of the fuel tank provided in the design or delivery set of the outboard motor (depending on the type of tank — see "Fuel tank").

The larger the capacity of the fuel tank, the longer the engine will be able to work without refueling, the less often it will be necessary to replenish the fuel supply in the tank. On the other hand, volumetric tanks have appropriate dimensions and weight, especially when filled; the latter is especially critical for motors with built-in tanks (see above).

The type of gasoline recommended for use in an internal combustion engine outboard (see "Engine Type"). In fact, this paragraph indicates gasoline with the lowest octane rating that is allowed to be used in the engine; higher rates are allowed, lower ones are highly undesirable, if not outright prohibited.

The octane number is an indicator that determines the resistance of a particular brand of gasoline to detonation (self-ignition during compression in the cylinder). Detonation is a very undesirable phenomenon, because. it leads to an increase in engine loads simultaneously with a decrease in its power and an increase in the amount of harmful substances in the exhaust gases. And this phenomenon occurs in cases where the engine uses gasoline with lower octane numbers than those for which the unit is designed.

Automobile gasoline, which is also used for refueling boat engines, is marked with the AI or RON index; the first option is used in the characteristics of east european motors, the second — in foreign ones. However, in both indexes, the number after the letters means the octane number. The higher this number, the more demanding the engine is on fuel quality. Thus, for example, a unit under AI-92 will be able to work normally with AI-95, but AI-90 or AI-87 cannot be filled into it. "Record holders" for unpretentiousness today are engines that can work even on the AI-76; but they are a rare exception to the general rule.

The types of gears provided in the design of the outboard motor are, in fact, the direction in which it can move the boat.

— Front. Standard gear for forward movement. Available in all outboard motors without exception, by definition.

— I'm neutral. In this case, neutral gear means the mode of operation of the motor, in which its shaft rotates idly, without transferring rotation to the propeller or water jet. Thanks to this, you can completely remove the thrust without turning off the motor and without lifting its “leg” out of the water. Considering that starting after a shutdown can be a rather troublesome procedure (especially if you have to do this often), and removing a spinning propeller from the water is generally undesirable — having a neutral gear is a very useful feature, and most gasoline engines (see "Engine type") have this mode. But in electric models (see ibid.), stopping and starting do not constitute a problem, so the role of the “neutral” in them is played by turning off the power and completely stopping the motor (and the neutral gear itself is not indicated in the specifications).

— Back (reverse). A mode of operation in which the engine pulls the entire vessel backwards; in propeller motors, it is implemented by rotating the propeller in the opposite direction, in jet engines, by using reverse dampers. The rever...se function greatly facilitates both manoeuvring in narrow spaces and emergency braking on the water, so it is found in the vast majority of gasoline engines and almost all electric ones.

Note that electric motors (see “Engine type”) can have several gears of the same type — for example, 5 forward and 3 reverse. In such models, each "gear" is a separate switch position corresponding to a certain engine power. In gasoline engines, power control is carried out smoothly, using a throttle, so they have less than one gear of each type.

The total weight of the outboard motor. This parameter is indicated, usually, only for the unit itself, without taking into account the fuel in the tank and the tank itself (if it is external, see "Fuel tank"), as well as additional equipment. Motor weight data can be useful in order to estimate the overall balance of the boat and the change in its payload capacity.