Yes, electric boats have horsepower, it is just usually expressed in kilowatts (kW) instead. The two units measure the same thing: power. The conversion is simple: 1 kW is about 1.34 HP, so a 3 kW electric motor is roughly 4 HP.
An electric motor often feels stronger than its raw number suggests. It delivers full torque the instant it spins, with no need to rev up, so a modestly rated electric motor can push a boat as well as a larger petrol engine in everyday use. This is why manufacturers quote an “equivalent HP”: treat it as a rough guide rather than an exact match.
The practical takeaway: do not simply copy the horsepower of your old petrol engine. Electric power is used differently, and most boats need less than people expect.
For how to size a motor properly to your boat, read electric boat motor power: how many kW do you really need.