What size motor do you need on a pontoon boat to tow a tube??

my brother in law bought a pontoon boat, it has a 90 horse power motor, we wanted to attach a tow bar to it, but at a cuople of hundred bucks for the bar i really want to make sure that it can handle it.|||as in tube you mean innertube? the type you get in and float around? if you do you have plenty of horse power way more than enough|||as in tube you mean innertube? the type you get in and float around? if you do you have plenty of horse power way more than enough|||well you are gonna need a lot if you want a semi-descent ride. i would reccoment tubing on a speedboat because it is WAY more fun.