Calculer la puissance administrative d'un moteur de bateau

In administrative horsepower (tax horsepower), horsepower or kilowatts, boat engine power is expressed in many ways. To calculate the annual registration and navigation tax (TAEMUP, formerly DAFN), only the engine power expressed in tax horsepower is of interest to us.

The pleasure boating experts at Bateau-immatriculation.com decipher for you all the ways to measure your boat's engine power and their usefulness.

Horsepower (cv in French) is a unit of measurement invented by James Watt, a Scottish engineer in the late 18th century. To assess the power of steam engines of his time, he estimated it based on the physical capabilities of a draft horse to pull a load.

Horsepower is commonly used but is not among the power units recognized by the international system of units.

This is why, on new pleasure boat registration certificates issued since 2019 in France, only powers expressed in Kw and CV (CV for administrative or fiscal horsepower, see below) are indicated.

The abbreviation for horsepower varies by country:

• cv for French-speaking countries
• hp for horsepower in English-speaking countries
• pk for Paardenkracht in the Netherlands, hence the unit used on ICPs (International Certificate of Pleasurecraft) issued by the Watersport Vetbond

This unit of real power, expressed in kilowatts (1kW = 1000W), is readily used for boat engines because it is the global standard.

The Watt is the international unit of power, named in honor of James Watt. One horsepower is equal to 0.736 kW, and 1 kilowatt (kW) is equal to 1.36 horsepower. Therefore, there is a possible equivalence between horsepower and kilowatts. However, there is no possible equivalence between power expressed in horsepower or kilowatts and administrative horsepower.

Expressed in CV (chevaux fiscaux), the fiscal horsepower (or administrative horsepower) is a unit of measurement used in certain countries for establishing the registration certificate of a land or sea vehicle.

Please note that the calculation of the fiscal horsepower for a car and a boat engine are completely different. Similarly, the formula used for calculating the administrative horsepower of a boat engine in France and in another country is also different. This is why the horsepower indicated on a "Dichiarazione di potenza" for a boat engine purchased in Italy does not correspond to the French calculation.

In France, for a boat engine, whether it's a sailboat or a motorboat, the fiscal horsepower calculation method takes into account several parameters: number of cylinders (N), bore in millimeters (A), and stroke in millimeters (C).

The bore is the internal diameter of the piston. The stroke is the distance the piston travels within the cylinder. These are multiplied by a different constant depending on the engine's fuel (diesel or petrol):

fiscal horsepower for a diesel engine = (315 x N x A2 x C) / 100,000

fiscal horsepower for a petrol engine = (45 x N x A2 x C) / 10,000

Taxable horsepower is used by French authorities to calculate the amount of the annual tax on pleasure boats, the official term for motorboats or sailboats. The result is systematically rounded down to the nearest whole number.

All engines, diesel or gasoline, installed on a sailboat or motorboat, whether inboard or outboard, are potentially subject to an annual registration and navigation tax, so their administrative power must be determined.

However, only boats longer than 7m hull length, or with an administrative power greater than 22 tax horsepower, are subject to the acte de francisation (today ship registration) and the payment of an annual tax.

Please note: the administrative power of your boat engine does not correspond to the actual power, displayed on the pleasure craft registration document.

You can find the fiscal power of your engine in the list that we update regularly. Feel free to submit a model to us, we will be happy to help you!

If you cannot find your engine model, you will need to obtain an engine technical sheet to determine the characteristics that interest us, namely the number of pistons, their bore and stroke.