Comparison Tohatsu M9.8BS vs HDX F9.8BMS

The duty cycle of the petrol engine (see "Engine type") installed in the boat.

— Duplex. Two-stroke engines have a good ratio of volume and useful power, besides, they are simpler in design and cheaper than four-stroke ones. On the other hand, they have a rather high fuel consumption and noise level, and gasoline and oil must be filled not separately, but as a mixture. Such a mixture must correspond to certain proportions, otherwise the engine will either wear out and heat up due to a lack of oil, or smoke due to its excess. However high-end motors can use automatic mixing systems (see below), eliminating the need for the user to manually prepare the mixture. However, even when perfectly proportioned, two-stroke engines burn a certain amount of oil along with gasoline, which is why they are considered dirtier than four-stroke engines.

— Four stroke. For the same working volume, four-stroke engines tend to have less power than two-stroke ones. They also require compliance with specific transportation rules. However, this is offset by a number of advantages — primarily relatively low noise levels and gasoline consumption. In addition, gasoline and oil are refueled separately into the engine — this is more convenient and economical than preparing a mixture; and during normal operation, the lubricant practically does not burn out, which also has a positive effect on the environmental frien...dliness of the engine. At the same time, such units are quite expensive, as a result of which the four-stroke cycle is typical mainly for premium outboard motors.

The working volume of a gasoline outboard engine (see "Engine type"). This term usually means the total working volume of the cylinders.

The larger this value, the higher the motor power, usually (see the relevant paragraph). At the same time, with an increase in the working volume, fuel consumption, weight and dimensions of the unit also increase; and power depends not only on this indicator, but also on a number of other factors — ranging from the number of strokes (see "Engine duty cycle") or the presence of turbocharging (see below) and ending with specific design features. Therefore, situations are not excluded when a smaller engine will have more power, and vice versa.

The diameter of a single piston in a gasoline (see "Engine type") outboard motor. In most cases, this parameter is purely reference; situations where data on the piston diameter is really needed are extremely rare — usually during the repair or maintenance of the engine.

The working stroke is the distance between the two extreme positions of the piston in a gasoline (see "Engine type") outboard motor. In most cases, this parameter is purely reference; situations where such data is really needed are extremely rare — usually during the repair or maintenance of the engine.

The type of cooling system provided in the design of the motor.

— Air. Cooling effected by contact of air with heating parts of the engine. Air cooling systems are extremely simple, they do not require the construction of complex circuits through which liquid must circulate — a fan is enough (and some models even get by with passive radiators — characteristic ribbed protrusions on heating parts). Another advantage is the ability to work effectively regardless of the presence of impurities in the water, which allows such engines to be used quite effectively in polluted and overgrown water bodies. On the other hand, the efficiency of such cooling is low, and it is suitable only for low power units — up to 15 hp. Also note that this option is usually indicated for electric motors (see "Motor type"): although the electric motor in them is often under water and cooled by water, not air, the key point in this case is the absence of a special cooling circuit in the design.

— Water. Cooling, carried out, in accordance with the name, with the help of water. Note that we are not talking about liquid, but specifically about water cooling: the water necessary for the operation of such systems does not circulate in a vicious circle, but is taken overboard and discharged there after passing through the circuit. This is the main difference between boat cooling systems and "land" ones. If we compare this type of cooling with air, then...water systems are more complicated and expensive, but much more efficient and suitable for motors of almost any power. Note that in inexpensive low-power units, water is supplied by gravity, due to the pressure created by the screw, and in more advanced models a special pump is used.

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.

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 reverse functi...on 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.