5 1/2 hp Johnson on 14/36 Polar Craft

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Eddie Mullins

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Just got my first tin boat, 14/36 polar craft john boat. It has a 70ish 5 1/2 hp Johnson motor on it. Motor seems to be running great, and looks like it turning lots of water, but moves the boat SLLOOOOWWW.

Maybe I'm expecting too much. Is this motor just too small for this boat? What should I expect from this set up? I have a larger fiberglass boat and I actually think the trolling motor on it moves it faster than Johnson is pushing this little guy.

Could a different prop help? or is this combo only gonna move at a snails pace?
 
what's fast for me could be slow for you. do you have any GPS readings so we have an idea how slow your boat is?
search youtube for videos of similar rigs to get an idea how fast it should be going.

the HP on earlier model johnson motors are rated at the shaft, the actual HP at the prop would be lower..

small motors are not meant to get you anywhere fast. but even my 2hp yamaha pushes better than up to 50lb electric motors. a small gasoline outboard has better power to weight ratio compared to an electric motor if you consider the weight of the battery.

here's a few things you can check to get the most out of small motors:
1. trim should be set correctly, set it so the boat runs at displacement mode. trying to plane with a small motor will only put stress on the engine.
2. see if the foam is waterlogged, adding unnecessary load on the boat.
3. you can monitor the rpm, if it over revs, then you need a different prop. but i doubt this because the big motors are the ones prone to over revving.
 
Thanks for the reply. Just watched a couple of youtube vidoes of the same / similar motor and they were easliy moving twice the speed I achieved. I also saw they created more of a defined wake where as I was just seeing water boil up behind the boat.
 
Maybe the shear pin is busted or the gears are bad. Put the motor in gear and put a little pressure on the prop to see if it will turn either way. You may want to disconnect the plug wires before doing so though. Hope it is the shear pin.
Tim
 
earl60446 said:
Maybe the shear pin is busted or the gears are bad. Put the motor in gear and put a little pressure on the prop to see if it will turn either way. You may want to disconnect the plug wires before doing so though. Hope it is the shear pin.
Tim

It want turn in gear by hand. I may not be describing this right, but its definitely turning and moving lots of water, but it not creating a wake, it like its just churning the water behind the boat.

Another suggestion I have gotten is to look at the depth of the cavitation plate and prop to the boat. Maybe its no mounted at the correct height / depth .

I'll break out the gps the next time I put it in the water so I can give more info.

Any tips on how to tell if the mounting location (height) is correct? or on adjusting the trim?
 
The cavitation plate should be right at the bottom of the transom, give or take a little. So the whole prop is getting water below the boat. Adjust the trim so your lower unit is perpindicular to the bottom of the keel of the boat. That 5.5 is not gonna get your boat on plane although I have to admit I am always surprised at the claims made on this forum concerning hp and mph.

Lets see some pictures of this setup, lower unit, prop, boat, etc..

Tim
 
You mentioned seeing a defined wake on videos vs your water just boiling up behind the boat. I don't think your boat is planing compared to the ones in the videos you are watching. If you are a really large person then this may never happen but lets try. Move your tilt pin to the slot nearest the hull thereby trimming the engine all the way in or down. Second, move as much weight forward as you can and see what happens. You also may have a high speed adjustment on the front of the carburetor. Turn this adjustment clockwise arond 1/8 turn at a time until the RPMs peak out then begin to sag a little. Back the adjustment up to peak then richen it (counter clockwise) around 1/8 turn. See if this improves your performance before you start looking for all kinds of mechanical issues. By the way, your shaft should not be perpendicular, on that set up you want the engine tucked under as far as possible.
 
Tried to post pic, but can't get on photobucket at work to upload (darn firewalls LOL).

The caviation plate is 3 inches +/- below the boat.

Pappy, don't know what you define as really large, I'm about 210 lbs : ) . One of the videos I saw was a 5 hp motor, with 2 grown men in a boat bigger than mine, definitely moving faster than just me and a couple of coolers in mine.

I should be able to get out this week end. I'm going to bring along my gps and the 50 lb thrust trolling motor off my other boat, and just see if I'm crazy, but I'm betting the trolling motor out perfoms the Johnson as is right now.
 
Trimming the motor as close to the transom will definitely help with that little motor. I had a 5 hp on my 16' semi-v and if I moved the pin just one extra notch out from the transom, my speed really went down (with identical load and placement). You might want to try a spacer under the motor mount to raise is up a couple of inches, as that should help too. The cavitation plate should be near to the same level as the bottom of your transom.
 
Raised the motor up a couple inches, shifted some weight forward and achieved a more defined wake, picked up speed quite a bit. Little rig will fly at 6 mph now LOL. Little motor runs like a top but I don't know if this set up is going to suite me.
 

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