It 100% depends on your desired speed/weight capacities and what gear ratio you use. I've seen people use as low as a 1 or 2 hp, but they were geared to have a lot of torque and very little speed. If you use an electric motor with more hp you will probably need to run it on 220v not 110v. So keep that in mind.
Not sure about power but if ur building one urself, make sure u have an emergency brake. Can be dangerous if someone gets tangled up or something. Otherwise that sounds like a pretty sick project
Also wondering about this, the motors I've been looking at spin way to fast for a ropetow, would it be better to buy a gearbox or attempt to make my own? I would just use a old pitbike or something but my neighbors are assholes
I’ve seen one made out of a 5hp Honda pressure washing engine and a go cart torque converter. It wasn’t super fast or powerful with multiple people on the line but it got the job done