Is a 25HP too big for my boat?

[bassin'frog]

Re: Is a 25HP too big for my boat?

Shoot, that motor looks like it just came off the show room floor. You shouldn't have any trouble selling it, once you get your 10 running.

I would measure the transom in the very center of the boat, from the top, to the keel. I seem to recall, that a short shaft transom is around 18" give or take a couple. I would have to measure one of mine, to know for sure. Short shaft is typical for jon boats anyhow, especially the style you have. If you see a long shaft motor, you'll know it, if you see a 5" extension between the lower unit and the mid section.

Just took some measurements: from bottom of transom bracket (where it rests on transom) to bottom of Skeg is 27"; Transom is 16.5"; Cavitation Plate is 3/4" below keel. I do have a 5" extension on it as well, you can see in the picture. So, with all that information, it makes me think I need a long-shaft for this boat? Thanks to all for your help.

 

[1946Zephyr]

Re: Is a 25HP too big for my boat?

The transome is indeed set up for a short shaft. The measurement for the motor should be taken from the inside of the transom clamp, to the cavitation plate. That should be close to the same length as your transom height. The cavitation plate should be at, or slightly below the keel. If you put a long shaft motor on there, the cavitation plate will be several inches below the keel.
Looking at your picture though, your motor is a short shaft, but the cavitation plate is a few inches below the keel. A long shaft, would have the 5" extension housing where the lower unit bolts up to the mid section. In later motors that were factory long shaft, they just built longer mid sections.

 

[striper89]

Re: Is a 25HP too big for my boat?

your boat could handle it just beef up the transom best you can and try to support the motor while ridding to and from your fishing hole its not always the motor running that tears the transom up but the bumpy riding to and from

 

[bassin'frog]

Re: Is a 25HP too big for my boat?

The transome is indeed set up for a short shaft. The measurement for the motor should be taken from the inside of the transom clamp, to the cavitation plate. That should be close to the same length as your transom height. The cavitation plate should be at, or slightly below the keel. If you put a long shaft motor on there, the cavitation plate will be several inches below the keel.
Looking at your picture though, your motor is a short shaft, but the cavitation plate is a few inches below the keel. A long shaft, would have the 5" extension housing where the lower unit bolts up to the mid section. In later motors that were factory long shaft, they just built longer mid sections.

Thanks Zephyr for the info. The cavitation plate is indeed 3/4" lower than the keel. For some reason I just assumed it was a long-shaft. It ran good yesterday on the lake, so I am assuming the motor is proper for the boat. Will be talking with the seller of the 18Hp later on tonite. If I can get that one I'll be all set. Will sell this 5.5, and rebuild and sell the 10Hp I got. Thanks again for everything.
Bob

 

[1946Zephyr]

Re: Is a 25HP too big for my boat?

Yea, 3/4" is about perfect. If youre cavitation plate was above the keel, then your motor wouldn't perform right. Those 18's are great motors. I think you'll love it. It won't be too much heavier than your 10 either. Maybe about 10 pounds difference. Personally, I wouldn't run a 10, unless it was a '57 or older. The older one's have much better lower units. The '58 and later had the same lower unit as your 5 1/2 and they didn't hold up as well. The 18's I believe are one of the top 2 best motors OMC ever built. I actually like the Big Twin class better, but that's only because the lower units are fully jewelled as well as the powerheads, whereas the 18's aren't. They're still every bit as reliable though and would take one, sooner than anything else.

 

[nwcove]

Re: Is a 25HP too big for my boat?

25 hp on that boat would be an interesting ride! but id love to have that lil 5.5 rude! too bad im so far away! road trip maybe??! lol (this "old outboard bug" ) is straining my marriage!)

 

[bassin'frog]

Re: Is a 25HP too big for my boat?

Hey Zephyr, picking up a '67 Fastwin 18Hp tomorrow for $220!!!! Runs, idles rough. Pick it up around 1pm.
Definitely excited.....

 

[1946Zephyr]

Re: Is a 25HP too big for my boat?

Cool. Those are great motors. It sounds like it may need be checked over if it's idling rough. Maybe points and/or carb.

 

[bassin'frog]

Re: Is a 25HP too big for my boat?

Picked up my new baby today!!! Pulled on starter rope a few times and it seems to have good compression. Will hook up compression gauge soon. Plan on replacing ignition system, plug wires, plugs, and carb rebuild. Haven't totally checked it over yet. Also gonna replace impeller (as a minimum) and inspect impeller housing. Think i will eventually install electric starter and may need some help with that.... Still have to finish rebuilding my 10 hp.... fun fun fun

 

[1946Zephyr]

Re: Is a 25HP too big for my boat?

You can get a visual of your coils and such, through the inspection hole on the flywheel.

 

[bassin'frog]

Re: Is a 25HP too big for my boat?

What does it take to install a starter? What, besides the starter do I need to purchase? Any help would be greatly appreciated... Thanks

 

[jasper60103]

Re: Is a 25HP too big for my boat?

What does it take to install a starter? What, besides the starter do I need to purchase? Any help would be greatly appreciated... Thanks

I'm not familiar with your motor, but you'll need the bracket, starter and solenoid. The bracket will be the hard part, but you can search ebay or salvage yards. If you're really lucky you'll find a parts motor dirt cheap with electric start.

 

[bassin'frog]

Re: Is a 25HP too big for my boat?

Thanks for the info. I saw a starter with bracket attached the other day on eBay, gonna check it out again. I assume you have to hook up a starter switch somewhere, what is the normal installation location for the switch?

 

[Daviet]

Re: Is a 25HP too big for my boat?

I just drilled a hole in the side of the lower motor cover and installed it there.

 

[bassin'frog]

Re: Is a 25HP too big for my boat?

I assume I hafta have a fuse between the solenoid and the battery?

 

[Daviet]

Re: Is a 25HP too big for my boat?

You don't have to go to the battery, pull the hot wire for the switch from the battery post on the solenoid. I didn't wire a fuse because there is nothing on that circut, from the solenoid to the solenoid, a couple feet of wire.

 

[bassin'frog]

Re: Is a 25HP too big for my boat?

Ok, got ya... thanks Daviet!

 

[clemsonfor]

Re: Is a 25HP too big for my boat?

I had a 1971 25 hp and my switch was on the lower cowl either on the front or the side, i cant remember. It was a homemade job. It worked good esp after i had starter rebuilt.