The ability to tow is not a HP issue, rather a brakes and suspension issue. Can you stop the extra weight? Can you properly support the extra weight so far back on the car?
The braking issue, well that has to do with the size of the brakes, the weight of the car not including the trailer and the tires. You'll know pretty quickly if your braking ability is up to snuff.
For the suspension, that has mostly to do with how you balance your trailer, i.e. how much tounge weight you have.
I've pulled some heavy monos around with a 25hp lawn tractor.
More important than your engines HP is it's Torque. Since HP = Torque x RPM, you want that Torque for the boat ramps and other slow speed grades. Otherwise, you wil lhvae to rev the engine to increase the RPM to get more power.
I've flown about a third of the way across the country in an airplane with only 65 hp.
In the market
Previous boats owned
'74 Pearson 30
'82 H18 Magnum
St. Louis, MO