I'm about to over power my boat with a Johnson.

[tal]

I didn't really want to start a thread like this but I feel it's the only way to get responses from people that may have experience in the matter. First off, I have read a few threads about people not recommending the overpower due to insurance, safety, liability, etc.

With that aside, I don't have insurance, but I am responsible for myself and others in my boat while on the lake operating my boat. I understand this part of owning and operating a boat, much like operating a motorcycle or sports car. Things can happen when certain variables exist.

All else aside, I have a 1989 Skeeter SD 80. It currently has a yamaha pro 50lf, which I've rebuilt the engine, rebuilt the carbs, gone over time and time again, and I'm done with it. It doesn't run worth a flip and is completely unpredictable. I have found a good deal on an older Johnson 115hp. My bass boat is a 16ft fiberglass boat weighing less than 1000lbs. The maximum coast guard rating for the boat is 80 hp. I'd be much happier with a 90 than a 115+ motor, but I can't find one in the price range.

Unless it's newer and in a different brand ($2000+) I can't find an inline 3 that would work well with my boat. So I'm stuck with a heavier and older motor, but one that lasts a long time. I almost had a local mechanic install a 115 johnson on the skeeter about a year ago, but backed out cause he didn't want liability incase things went bad. So I believe the boat would actually handle a 115hp. I just want to know what everyone thinks.

I'm afraid of the negative comments that might come. I just want to know if someone has first hand experience with this stuff.

 

[hamburgerman]

Re: I'm about to over power my boat with a Johnson.

I HAVE A 1986 115 ON MY 16 FT. CHARGER IT DOSE FINE
5200 RPM AND i GET ABOUT 48 MPH OUT OF IT FAST OUT OF THE HOLE

 

[Lion hunter]

Re: I'm about to over power my boat with a Johnson.

I really think your asking the wrong forum. When you take on a task such as this your kind of on your own. I really doubt that your going to find anybody that you can trust to say it's a good idea. The ratings are on a boat for a reason. It's not all about liability. If a manufacturer thought they could sell you a bigger motor for more money they would. This is not a simple question of 10% increase which could be a waffle factor in how the motor was rated. Your over powering by 50%. You can't really put safety aside when asking a question like this. Safety is the reason a boat is rated as it is.

 

[tx1961whaler]

Re: I'm about to over power my boat with a Johnson.

Won't go into the overpower thing, but the weight of the motor may make the stern of the boat sink lower than you'd like. Was it on the low side with the 50? Did you get alot of water over the back when coming off of plane?

 

[asdasc]

Re: I'm about to over power my boat with a Johnson.

I agree with TX1961Whaler, I would be more concerned about the weight than the power. While the power COULD get you in trouble, a little common sense will keep you at safe speeds, and without common sense your boat is dangerous to yourself and others anyway.

I would compare the weight of an 80hp from the same era as your boat with that of the 115 you are planning to mount. Maybe a little extra bow weight will compensate some for it. The other thing is the sturdiness of the transome. If it is at all rotted, this would finish it. I would definately look for any flexing during the mounting procedure. Can you hang on the back of your motor on the trailer or on the water, just to see what happens?

I am not telling you what to do, just telling you what I would be looking into if I were thinking about it.

 

[tal]

Re: I'm about to over power my boat with a Johnson.

The back of the boat sits easily 6 inches or more out of the water with the 50hp and 3 adults sitting towards the rear of the boat. The only time I had water come over the back is stopping abruptly with someone sitting on the rear swivel chair (which they shouldn't do anyhow) on the back deck. I was going slow and plowing then stopped and it splashed up a bit. The yammie is really pathetic on the back. It has to be trimmed so low to get on plane, the little motor looks like it's sinking foot under the boat. It's way under powered at this point, especially since it doesn't run right.

Besides using a bit more gas, the Johnson I'm looking at is a 1976 model. My father has a '75 on his glastron cv-16. Only thing that went wrong with it has been powerpacks and carb cleaning. I'm hoping to get the same results with the '76. It is completely rebuilt as well.

To the above post - I stood on the cavitation plate of the 50 horse out of the water and bounced up and down and the transom doesn't bulge or budge. Seems solid. No rot. I weight 160lbs and I think the 50 hp weights around 180-190. So pretty close for what I hear these older motors weight. If on the water and I do it, it will sink a bit, maybe a couple inches.

What I'm wondering is will it point straight up in the air like all the boats on youtube do when they're over powered?

 

[a70eliminator]

Re: I'm about to over power my boat with a Johnson.

That depends on the trim angle, with enough power and trim in the exact opposite can be achieved dunking the bow.

 

[bashr52]

Re: I'm about to over power my boat with a Johnson.

My 13ft whaler with a 40 horse will put the front end up in the air to the point you have to stand up to see over the bow if theres no weight up front and you take your time getting up on plane (not to mention having to start down wind and turn around once on plane if you want to travel into the wind). It was sold from the dealer with this engine, and its the max you can put on it. Once on plane the thing settles right onto the water nicely.

One benefit you may have with the bigger engine is not having to run it at full speed all the time to move around. Your gas consumption may be a wash considering you can now motor around at 1/2 to 3/4 throttle, where as you needed full with the smaller engine........

 

[JB]

Re: I'm about to over power my boat with a Johnson.

Excuses and rationalizations are irrelevant, overpowering a boat is a dumb and dangerous thing to do. That is even more true with a flimsy boat.

Stay under the 90HP.

 

[xxturbowesxx]

Re: I'm about to over power my boat with a Johnson.

your current motor weighs 164lb and the 115 will weigh 306lbs. I would say not to even try it.

 

[a70eliminator]

Re: I'm about to over power my boat with a Johnson.

I had reservations about putting an 80hp on my 60hp rated boat but it was either that or nothing at the time, basicaly the same engine just larger bore, weight difference only 3 lbs. I have no regrets whatsover, I wouldn't have even know the difference. Your swap is more drastic and with the weight difference you looking at you would have possibly a borderline dangerous rig, my opinion is not biased, I'm all for it under the right circumstances.

 

[tashasdaddy]

Re: I'm about to over power my boat with a Johnson.

put a 3 cylinder 70 on it. less weight, great power.

 

[kenmyfam]

Re: I'm about to over power my boat with a Johnson.

Plain and simply it is a bad idea. Stick within the boat's limits and make sure your set up is good.

 

[5150abf]

Re: I'm about to over power my boat with a Johnson.

Engine weight has NOTHING to do with the transom rating, it is the torque the engine puts on the transom that is rated.

My boat is rated for a 70 but I could hang a 350 yamaha on it and the transom would hold the weight BUT as soon as I hit the gas the engine would rip the transom right off the boat.

If you do this your transom will fail at some point, more than likely at full throttle since that is the highest stress then you have a 300lb motor running full throttle in the boat with you as you sink.

Sounds like a party to me.

 

[tal]

Re: I'm about to over power my boat with a Johnson.

Well I definately don't like the thoughts of it ripping through my transom. I would like to find a 3 cylinder 70 or 90 but there seems to be none around at a reasonable price.

I guess I'll reconsider the swap.

Thanks for the thoughts guys.

 

[crxess]

Re: I'm about to over power my boat with a Johnson.

I decided to wait and see what was said.

My turn -

Power increase is NOT your concern. common boating sense can overcome that point. Racers Overpower all the time for more speed through better component matching.(machining/tuning)

Your critical failure is NOT understanding structural integrity. If not right away, soon the weight of that motor will destroy your boat and unfortunately may take you/your passengers/others near by with it.

A motor Does Not push a boat in the way we all reason. In order to do so the prop woould have to be directly behind the transom.

The prop of the motor actually tries to drive itself under the boat with a tremendous twisting force against the transom. The energy is dissipated out through the transom into the hull lifting the front.

The added weight of the motor you want to use will greatly increase that twisting force eventually cracking and delaminating the transom.

If you don't accept this, ask yourself.
WHY is motor height so critical to GO FAST Boaters?

 

[Charlie in TX]

Re: I'm about to over power my boat with a Johnson.

Evinrude made a V-4 down to 80hp. If you put 80hp carbs on the 115 you would CG legal. Proceed at your own risk. If it were me, I would put the 115 on.

 

[Faztbullet]

Re: I'm about to over power my boat with a Johnson.

The 115 year model your looking at is not a prop rated engine as the newer ones are and is only putting out around 90 hp anyway. I would not be scared of it hp wise but more concerned due to weightand would lean more toward a 70/75 3 cylinder as suggested. Motor height has nothing to do with transom stress, it reduces drag of engine in water. Also boats are rated by a formula:
(2 X L X W) -90 = rated horsepower
Where:
L=boat length
W=transom width; if the boat does not have a full transom,
the transom width is the broadest beam in the
aftermost quarter length of the boat.

The rated horsepower may be rounded up to the nearest "5".

Also it is not a violation of Coast Guard regulations to install or use an engine larger than specified on the capacity label, but there may be state regulations prohibiting it, and restrictions from your own insurance company regarding this.

I run my overpowered boats for fun and sport and correctly set up have no transom cracking/damage or twisting as suggested.

 

[gazza2007au]

Re: I'm about to over power my boat with a Johnson.

50hp to 115hp is a big jump i recently brought a boat 17 foot runabout it had a 135hp evinrude on it yikes!!!!!!! i have down graded to a 70hp as i personally think the engine was way over the boats limit i never took the boat out while it had the 135hp on it i thought that was the most sensable thing to do nothing worse than hearing a loud crack at WOT to see your motor going faster than your boat
good luck

 

[bktheking]

Re: I'm about to over power my boat with a Johnson.

It's like putting a big block in a chevette. If you want to go faster buy a faster boat, they put ratings on these boats for a reason, why risk you , your friends and family and other boaters like me with my family out on the water just to go 10 mph faster, cars are one thing but boats are entirely different.