With the advent of electric motors, whose commercial power output is expressed in watts (the multiple of which is kW or 1000 W) rather than horsepower, the question may arise as to whether, and over what power, a boat license is necessary. Being accustomed to associating the 40-hp limit with the maximum power of engines for which a license is mandatory and not being clear to everyone what these acronyms express, let us clarify.
Horsepower (HP) and watts (W): what they are and what they have in common
The horsepower is a unit of measurement that is used to indicate the physical power of motorized means of transportation. It originated at the beginning of the Industrial Revolution to get an idea of the productivity of powered machinery, that is, how much horsepower could be replaced by the machine. It is equivalent to lifting a weight of 75 kgf (kilograms force, what we call kilograms, although it is a misnomer) at a speed of one meter per second.
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Although in common use, horsepower is not a unit of measurement in the International System, and as its value in the past changed from country to country (British horsepower was calculated differently) and its symbol was different depending on the language, A European Council directive banned its use in favor of the watt (also of kgf, ed.). The watt is the unit of power in the International System; it owes its name to James Watt for his contribution in the development of the steam engine.
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The conversion of electric motors: from HP to W
Converting from HP to W is quite simple, just multiply the horsepower value by 0.735 (approximately). Thus making 40 hp is 29.4 kW. For the reverse operation, it will suffice to divide by 0.735. This helps us understand how powerful the electric motor will be, the value of which is normally expressed in kilowatts (kW).
When a boat license becomes mandatory
The Recreational Boating Code (Legislative Decree No. 171/2005), having to comply with the European directive, tells us in Article 39 paragraph 1 (b) that a boating license is mandatory “with power greater than 30 kW or 40.8 hp. “