One of my buddies has a 12ft jon boat that's rated for a 6hp. It's only a year old and in great shape. Our other friend just bought a 9.5 johnson (64 model totally redone on the inside). Do you experienced guys think it'd be ok to use the 9.5 on the 12ft jon boat? Thanks for any advice in advance!!

Sure, if you want to go 60 mph in a jon boat.

Seriously... the transom might not hold up.

with the 64 yr. model engine, it won't be a horsepower to weight ratio problem.

it might be more of a weight problem of that older engine.

there's a reason they rate to boat

You should not have too much of a problem. Just watch the out how much weight you load in the back of the boat. Keep the weight spread out. Do'nt get on the engine too fast. Get into it slowly and get it under control before you show how fast it will go.

I have a heavy old 1955 10hp Johnson on my 12 flat bottom with a semi V on the front. Not really a jon, but flat on the bottom. I don't have any problems, but can't always go wide open. When the water is flat it will go 18 mph by the GPS. Have the trolling motor battery close to the middle to help with weight. Just take it easy and you should be fine. I replaced my transom that was rotten (boat is a 70's model bought from Gibsons back in the day)with a plywood sandwich. The middle brace broke many years ago and I just put a 2 X 4 between the transom and rear seat. Doesn't flex the transom. I also ran my buddies 64 9.5HP on it the other day with no problems. The same speed as my 55HP wide open.

'Nother tip- relocate your gas to the front of the boat if you run by yourself a lot.
We run our battery in the back and fuel in the front of our duck boats. Makes shallow water easier to access and if we are alone it keeps the nose down and the back up.

thanks so much for all the information guys!

Doubt that old '64 is still making 9.5HP anyway. I'd try it.