6, 9.9, 15HP on a 12ft tinner

perki307 · Dec 7, 2024

I've been running an old 6hp evinrude on a 19633 12' montgomery ward sea king and getting right about 15mph consistently. The motor is solid. Starts first pull almost every time! The weight/size/speed is 'fun' and I keep thinking, this will be perfect for the grandkids in a couple years so I don't really want to get rid of the motor. I just wish I could get a little further out the river a little faster.

Has anyone 'upgraded' a motor from a 6hp? Curious where folks ended up. Boat is rated at 10HP I believe.

Thanks for sharing your experiences/comments!

lckstckn2smknbrls · Dec 7, 2024

Are you thinking of staying with a 2 stroke or moving up to a 4 stroke?

Crazyboat · Dec 7, 2024

I'll give you firsthand numbers and opinion from back in the mid/late 70's. Me and a bunch of friends had about every motor you could think of back then. From a 3.6 merc all the way up to a 15 Johnson.
3.6 would barely get on plane in a 10' tin jon boat. Once it did maybe it hit 10 MPH
4 HP Sears pretty much the same.
4.5 Sears maybe 1 MPH faster and just as slow getting up.
7.0 HP from Western Auto and V bow about 14 MPH.
7.5 Merc on a fiberglass hull, 14 MPH.
7.5 Sears on a tin 12' "V" bow 14MPH
10 HP Merc really set a new standard at 28 MPH (Upgrade from the Western auto eng)
15 Johnson, 28 MPH. (Upgrade from the 7.5 Sears.)

Yes, the 10 merc and 15 Johnson ran neck and neck, I had the 15, friend had the 10. That merc was amazingly fast.

That said, I could pull a 140 pound skier, the merc could not.

May well have been the props. That speed for a young kid wil get them in trouble. I was 15 at the time.

airshot · Dec 7, 2024

10hp on a light weight tinnie will get an inexperienced boater in trouble quickly!! Any wake or other waves at high speed can cause a novice to loose control. If your set on moving up to a 10 hp, consider making a throttle limiter so the youngsters don't get carried away until they gain experience.

oilsmoke · Dec 8, 2024

I've had several 12ft V hulls over the years, the best was a Duranautic, the fastest was a Sears hull from 1970.
I ran everything from a 3hp Evinrude to an 18hp Johnson.
Anything under 10hp would not get on plane, 10hp and larger had freeboard issues at the transom due to weight.
With the 10hp (Evrinrude 2 stroke), I had to use a tiller extension and ride as far forward as possible when alone, or have a passenger ride up on the bow. The 18hp was scary, even with a 250 lb passenger up front the bow would raise up out of the water on take off unless I feathered the throttle.
The 9.9hp Evinrude would plane the boat with just me, but struggled with a passenger.
The Sears boat was more forgiving but I soon found a 14ft that made the 9.9hp the only choice, until I found a 15hp. The added couple feet of hull length both helped the freeboard issue and the planing issue.

The Duranautic 12 was more stable though, I could stand up in that boat with no issues but the 12 and 14ft Gamefisher hulls were a tippy as a canoe.

A lot has to with your own weight too when dealing with smaller, lighter boats and small motors.
Myself, at 350lbs, eventually made a 12ft hull a poor choice with anything but an electric trolling motor and forward mounted battery. I eventually sold all my 12ft and smaller 14ft boats in favor of a 16ft hull with a 35hp, and later a 50hp for a bit but ended up going back to the 35hp. The loss of freeboard with the 50hp was too much to overcome vs running lighter with the 35hp.

TriBull · Dec 9, 2024

perki307 said:
I've been running an old 6hp evinrude on a 19633 12' montgomery ward sea king and getting right about 15mph consistently. The motor is solid. Starts first pull almost every time! The weight/size/speed is 'fun' and I keep thinking, this will be perfect for the grandkids in a couple years so I don't really want to get rid of the motor. I just wish I could get a little further out the river a little faster.

Has anyone 'upgraded' a motor from a 6hp? Curious where folks ended up. Boat is rated at 10HP I believe.

Thanks for sharing your experiences/comments!

I started with an old 6hp 2stroke Yamaha that the wife of a very close buddy gave me when he died. It was a long shaft kicker he used as an auxiliary motor in his larger boat.
I accepted it with the notion of setting up a small boat for exploring Florida rivers, lakes and coastal areas. I hung it on jack plate mounted to a 12’ StarCraft. But it didn’t take long to snap the tiller completely off while trying to tilt it out of thick weed. That motor ran good, but barely got the boat up on plane… I replaced it with a new 9.9 4stroke Yamaha, which was a game changer! I think it’s the perfect set up. I get 23mph+ solo, and can still get on plane with a passenger or two… The new motor is a short shaft, but I still love having the jack plate.