It's all about strength of wind and sea direction.
My 35 hp Volvo, operating at about 1700 rpm, easily towed a 35 ton fishing boat in the canal here. It's a while back, but we towed him quite a distance, perhaps 10 miles.
I would never have risked it on Loch Ness though, in anything other than flat calm.
If you yourself are being towed and there is a swell running, remember to buoy the two line. If the tow gets out of synch', it tends to wrap around rudders and tear them off, or bend them flat, and things like that.
And do not tie the tow line to the mast foot. Please don't. If the tow gets out of synch', and the tow line goes tight suddenly, and your rig is not that tight, you are going to risk pulling the mast down.
Line around the rudder is somthing I have not considered, good point.