Your going to get a whole bunch of folks posting about not going over the max hp of the boat, bla bla bla.
so get ready for all of that
but down to the facts,
my uncle has a 22' lowe that had a 60 on it. 2 toons and was getting 25 - 26 mph with that set up, then added the center toon to make it a tritoon, it raised the back end up about 4" and the front about 2"and only gained 1-2 mph.
then we put on a 140 hp evinrude, (same controls,cables ect) and gained anoother 3-4 mph tried diffrent props and the fastest one is a 15 pitch,, wouldnt turn a 17 or 19 too low of rpms
He is more happy with adding the 3rd toon than the 80 more hp for what its worth
Rating is about how much weight the transom is designed to hold, more than anything else. I have seen MANY pontoons with 150's on the back. I'd say that the diameter of the logs comes into play as well, most of the toons I've seen with more than 100hp on the boat had 25" logs VS 20" logs.
I think the key to answering your question lies in how you intend to use the boat. Are you going to pull skiers or tubers or is it going to strictly be a fishing boat? I had a 21 footer with 40 hp motor and it was a little slow to me but I'm not normally in a big hurry. I wouldn't go over the rated horsepower as has been stated and remember those horses come at an added fuel cost.
1976 pontoon boat how much hp is suggested any ideas
It being a 76' model, it probably came with something in the 50 hp range.
As was posted above, higher hp on a pontoon doesn't make for much more speed. They'll only go so fast. More HP will tend to bust up the older pontoons.
When i got my boat, it had a 40 hp outboard and it is a 24 ft tracker fishing barge
the only outboard i had was a 115 hp mercury, I was conserened with the physical weight of the outboard more than the rated hp of the engine. Ive had it on for about 3 years and have not had any problems yet. I do check the transom bolts and pan for breaks and rips but good so far. i think the breaks and rips would come from viberation more than any thing.
So you might keep some of these in mind when you mount you outboard,good luck and happy boating...