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I'm not a boat guy type of question re: HP

1981K20

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Yea I know, not a boat site. But boat forums suck

I have a 12ft 1968 aluminum boat w/ 15hp Johnson. Markings to indicate max HP are long gone. Goes ok, but is a '76 Johnson and leaks out propeller, sputters at mid range rpm and is simply just old and tired.

Anyway, picked up a nice 20hp Yamaha for cheap but now I'm hearing that some people don't think that's a great idea whatsoever and it's a good way to cap size or drown.

So I guess my question is what's the biggest size motor you've ever had on a 12 foot aluminum and how did it work out for you?

Worth noting that I go on inland lakes for the most part and the boat will never see open water
 

Alpine4x4

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You'll be fine. Its probably over the rating, but a 20hp isnt going to make you kill a bus load of nuns. We always ran 9.9's or 15's. Usually ran 9.9's so you could avopid having to register the vessel. Neat trick is most 15's are just bored and tuned 9.9's so the cowlings swap...:grinpimp:
 

Arickvan

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i looked into some tiny bass boat stuff and that is on the larger size for a motor

but take it easy on the turns and it should be fine right? :homer:
 

TRINDU

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Never had an aluminum boat, but a 14ft skiff with a honda 50, because the Yamaha 30 wasnt enough powah.

If its magable weight wise, I'd run it. Right now my 19ft is "rated" for a 140. But I have a 150 merc hanging off the back... which is the same block/motor as the 225. Love it.
 

Rerock

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I had a fresh 9.9 on my 12'. Based off that 20 would be fine, but be mindful of wave size and turning radius.

Just because it has power, doesn't mean you need to use all of it...
 

woods

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40HP on the 13' Whaler. If its calm enough, it moves right along. :cool2:
 

Ebs

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As long as they weigh close to the same you are okay. See youtube for big dumb outboards on tiny boats, pretty much does nothing but 5 mph wheelies.
 

Deuce 40s

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Around here a lot of guys weld on flotation pods to the transom for more stability. They swear by them.
 

WTF?

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20 hp on 12' will be completely fine. adjusting the mounting height of the motor will have huge gains on that size boat. if the outdrive is too long/ mounted too deep, your leaving speed & efficiency gains on the table.



I agree, boat forum people are dumb.

So much this^

Boat people make the towrig section rating nazis here seem like reckless wildmen. they're a bunch of pearl clutching bitches when it comes to modifying anything or pushing ratings etc...
 

ConwayMuddy

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I hang a 35 off the back of a 14x48 flat bottom aluminium. I'd go bigger but I'm afraid the boat will fall apart. Pretty sure it was only rated for oars.
 

Snowbird13

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Not the sane thing, but I had a 25 on a 12 foot rubber raft. That was fun:smokin:
 

The Beens

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Do you have the title to the boat? If you do, it should have the manufacturer/dealer where it came from listed on it. Assuming they are still in business, you can contact them with the Serial No. and they will be able to send you a new loading/HP placard. You're going to need that on the boat anyway if you ever get checked by fish and game. (<- Missouri Rules, your state may differ.)

Secondary beg off clause....ignore completely if canadian.

If the 20hp is approximately the same size and weight distribution with approximately the same center of gravity...you'll be fine.
 
Last edited:

87manche

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Never had an aluminum boat, but a 14ft skiff with a honda 50, because the Yamaha 30 wasnt enough powah.

If its magable weight wise, I'd run it. Right now my 19ft is "rated" for a 140. But I have a 150 merc hanging off the back... which is the same block/motor as the 225. Love it.

this. chances are newer 20 horse is lighter than ancient 15, so it'll be fine.
 

RobC

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FYI, you may not find a tag on it most likely. Had a ‘72 richline that didn’t have one. I think ‘73 was when the gubment made it mandatory. I called the highway patrol thinking I was going to have problems before registering it and they didn’t even know that info.
 

Rockbuggy84

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Sell it and do a jetski conversation on it.

Huh?

Back On topic, weight shouldn’t matter if it’s like newer outbaoards. Many manufacturers use the exact same engine and change the tune or carb for hp.

For example, my Tohatsu 9.9 kicker is identical to the 15 and 20hp. I can order a 20hp ecm. Tohatsu, Honda, mercury and many more do this.
My 225 Honda is identical to the 200 and 250 other than the tune.
 

Shortthenlong

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I run a 25hp 2 stroke on my 12ft. It replaced the previous 25. Yes you don't need full throttle all the time but it is nice to have. Mine is quite a deep V by tin boat standards so the hp helps. Just need to be a bit aware of weight distribution

Matt
 

kf4zht

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40HP on the 13' Whaler. If its calm enough, it moves right along. :cool2:

I've got a 35 on a 13 whaler. Can confirm, it scoots. Picked up a new prop and hydrofoil, going to try and squeeze a few more mph out of it. Maybe the wake will hurt less faster.

Have heard of guys running up to 60s on the 13'
​​​​​​
 

Chevy_man

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That old 15 probably weighed more than a new 30.

Run it, it'll be fine.


I run my 14 (empty aluminum with a few wood seats) off a trolling motor. It'll turn around on itself, so you may want to adjust the steering stops so you can't get too stupid.
 

tracyb

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I've got a 35 on a 13 whaler. Can confirm, it scoots. Picked up a new prop and hydrofoil, going to try and squeeze a few more mph out of it. Maybe the wake will hurt less faster.

Have heard of guys running up to 60s on the 13'
​​​​​​

i had 35 on a 35 whaler for one crabbing season. i thought it was horribly underpowered.

now i have a 20hp on some freebee 12' aluminum. once i got the mount height, trim dialed its perfect for the crabbing and fishin i do. Deception pass area Wa
 

1981K20

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Do you have the title to the boat? If you do, it should have the manufacturer/dealer where it came from listed on it. Assuming they are still in business, you can contact them with the Serial No. and they will be able to send you a new loading/HP placard. You're going to need that on the boat anyway if you ever get checked by fish and game. (<- Missouri Rules, your state may differ.)

Secondary beg off clause....ignore completely if canadian.

If the 20hp is approximately the same size and weight distribution with approximately the same center of gravity...you'll be fine.

Yep, Canadian so no clause or anything. It's a Harbor Craft, has a tag but it's really worn. Weight is pretty close but newer motor is huge compared to it. Should be fun, trying it Sunday and will post a reply if I'm still alive

thanks to all for the encouragement, one doesn't simply make irrational or dangerous decisions without some positive reinforcement from random people on the interwebz
 
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