Comparison Mercury F9.9M vs Mercury F8M

The maximum operating power of the outboard motor, expressed in horsepower.

Horsepower (hp) has traditionally been used primarily to refer to the power of internal combustion engines, including gasoline engines (see "Engine type"). However, in outboard motors, these units are also used for electric models (see ibid.). This is due to the fact that the majority of gasoline engines are on the market, and boat manufacturers prefer to indicate the maximum recommended engine power in “horses”.

The general patterns when choosing outboard motors in terms of power are as follows. On the one hand, a more powerful unit will allow you to develop more speed and is better suited for a heavy boat (see "Maximum boat weight"). On the other hand, weight, dimensions, cost and fuel/energy consumption also directly depend on power. Therefore, it does not always make sense to chase the maximum performance.

In addition, the choice of motor for maximum power also depends on the characteristics of the craft on which it is planned to be used. It is not worth exceeding the recommended power stated in the specifications — firstly, the boat transom may not be designed for a heavy large-sized unit, and secondly, the boat itself may not be suitable for acceleration to high speeds. There are also more specific recommendations. For example, from the point of view of efficiency and safety, the engine power at the level of 60 – 80% of the ma...ximum specified in the characteristics of the boat is considered optimal. Lower values may be useful if economy and low noise level are important to you, and higher values if high speed and acceleration dynamics are key points.

There is one more specific point associated with this parameter: most often, the characteristics indicate the power output directly to the propeller, however, some manufacturers (mostly east european) can go for a little trick, indicating the power on the main motor shaft. When power is transferred to the screw, losses inevitably occur, so the useful power of the motor in such a case will be less than claimed. Thus, when choosing and comparing, it's ok to clarify what kind of power is meant in the characteristics — on the propeller or on the shaft.

The maximum operating power of the outboard motor, expressed in kilowatts.

The practical value of motor power is described in detail in “Maximum power" is higher. Here we note that the kilowatt (derivative of watt) is just one of the units of power used in fact along with horsepower (hp); 1 HP ≈ 735 W (0.735 kW). Watts are considered the traditional unit for electric motors (see "Engine Type"), but for a number of reasons, outboard motor manufacturers use this designation for gasoline models as well.

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 gear ratio describes how fast the propeller of the outboard motor rotates relative to the speed of rotation of its shaft. For example, a gear ratio of 2 means that for each revolution of the shaft, the screw, in turn, makes two revolutions (that is, it rotates twice as fast). In modern outboard motors, this parameter, in fact, is purely reference, because. the practical characteristics of the unit (power, traction, etc.) depend on many design features and are practically not related to the gear ratio.

The design of the propeller supplied with the appropriate type of outboard motor (see above). In this case, the simplest division is used — by the number of blades.

This indicator actually refers to reference, and not practically significant, because. the practical characteristics of the propeller depend not only on the number of blades, but also on their shape and length, and a number of other indicators (power, thrust, etc.) affect the general characteristics of the motor. In addition, manufacturers tend to select propellers based on the best match with the desired capabilities of the motor.

The presence of the motor rev limiter.

This function is most often implemented in the form of an automatic system that prevents overloads and overheating of the engine: when the temperature rises critically, fraught with overheating, the automation reduces the engine speed, allowing it to cool down (or at least not heat up further). Of course, when the system is triggered, the speed of movement decreases, but this can hardly be considered a serious nuisance compared to a motor breakdown.

Types of indicators that can be connected to the motor. The indicators provide a variety of additional information about the operation of the motor and can be useful for various purposes related to the management of the boat. Note that compatibility with a particular indicator only means that the motor has the appropriate sensors — the indicator itself usually needs to be purchased separately.

— Speedometer. An indicator showing the current speed of the boat. Note that the speedometer data is based on the speed of the water flow relative to the vessel; in other words, it shows speed over the water, not over the shore, and in strong currents, the actual speed of movement can differ markedly from the data from the speedometer. However, for simple navigation tasks, this is quite enough, but for complex ones, there are more advanced methods for determining speed — for example, according to GPS data.

— Tachometer. An indicator showing engine speed. Allows you to control the mode of operation of the motor and prevent a critical excess of speed (fraught with increased wear and even an accident). The difference between the tachometer and the overspeed sensor (see below) is more detailed information — this indicator works constantly, providing the driver with information about the speed both in abnormal and in normal operation.

— Hour metre. A syst...em that counts the total operating time of the outboard motor. Hours data is extremely important for engine maintenance and failure prevention: for example, in many models, the frequency of oil changes, general maintenance and other similar procedures is tied precisely to the number of engine hours. In addition, the total resource of the motor is described precisely by the time of its operation.

— Oil pressure. Engine oil pressure indicator. A decrease in this pressure is a sign that there is little oil left or there is a problem in the lubrication system; the indicator provides early warning of such troubles, preventing situations where the engine is left without lubrication (which not only increases wear, but is also fraught with jamming and an accident).

— Oil temperature. The indicator showing the temperature of the oil in the engine. High oil temperatures are undesirable not only because the oil loses its properties — it is often a sign of serious problems in the engine.

— Oil level. An indicator showing the amount of oil remaining in the engine. Allows you to estimate the amount of lubricant available and, if necessary, take measures to replenish its supply.

— Battery charge. An indicator showing the battery charge level. It is most often found in electric motors (see "Engine type") and plays the same role in such models as the remaining fuel indicator (see below) in gasoline — that is, it informs the user about the energy reserve. However, gasoline units with an electric start system (see above) can also be equipped with a charge indicator — so that the user can monitor the condition of the battery and take timely measures to recharge it (otherwise, at the most inopportune moment, you can be left without the ability to start the engine).

— Remaining fuel. An indicator showing the amount of fuel remaining in the tank. This feature allows you to control the fuel supply and reduces the likelihood of being left with an empty tank at the most inopportune moment. However the information from such indicators is rather approximate — nevertheless, it is quite sufficient for successful application in fact.

— Fuel consumption. An indicator that displays fuel consumption in the current mode of engine operation. Allows you to evaluate the economy of the selected mode and determine how long the available fuel will last; especially effective in combination with the remaining fuel indicator described above.

— Engine overheating. An indicator signaling a critical increase in engine temperature. A similar phenomenon can be both a consequence of a malfunction in the motor itself, and the result of external influences (for example, a long stay in direct sunlight); however, anyway, overheating is fraught with various troubles (from jamming to fires and even explosions), and a timely warning about it will definitely not be superfluous.

— Engine overspeed. An indicator that provides warning of a critical increase in engine speed. Unlike the tachometer described above, it works only in emergency situations and does not provide data on a specific number of revolutions.

— Trim positions. An indicator that notifies the user of the current position of the trim (leg) of the engine. It is convenient because to clarify the position of the leg, you do not have to turn around and look at the engine every time.

— Throttle positions. An indicator that informs about the current throttle position — and, accordingly, the power that the motor should give out. It allows not only to control the engine operation mode, but also, in combination with other sensors, to diagnose various problems: for example, the lack of throttle response to the movement of the engine control knob indicates a malfunction in the remote control (see "Control system").

— "Water in fuel". An indicator that warns of the presence of water in the fuel entering the engine. The ingress of water into the fuel leads to a decrease in engine power and interruptions in its operation (since the water does not burn, the combustion energy in the cylinders drops), and a large amount of foreign liquid leads to the so-called water hammer, severely damaging the engine. The indicator warns of such phenomena, and in most cases it is able to work long before the described effects become visible to the “naked eye”. This allows you to take action in advance, before the consequences become dire.

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.