Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

[hunterfab]

My 93 Thundercraft 156 SS 16.5ft is rated for a 90 horse outboard. I just picked up a real nice Force 125 outboard and would like to install it. I am worried about any potential problems with going past the rated engine size.. Has anybody ever done this and what kind of problems can I expect? Or is it just a stupid idea and should I just stick with what the factory says I should go with? Just looking for a little more power to tow tubes and to pull a skier. Hate to sound ignorant and ask a stupid question but I figured it would be best to ask before I just went and installed it.. Thanks in advance for your advice

 

[a70eliminator]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

I'm going to have to say no, your reasoning tells me you need a bigger boat with a bigger motor.
If you used the boat conservatively for fishing and cruising to and from spots than yea, just put batteries and fuel tanks forward for balance and watch your payload. But for doing watersports you'll more than likely compromise the transom and potentially sink your boat.

 

[md-lucky]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

Around here, the Sheriff checks for things like that..

I've never personally dealt with them, but a friend of a friend had his boat towed back to the boat ramp by the Sheriff for having 1 persona more than what the plate said in his boat. They wouldn't even let him turn the thing back on until he dropped off 1 person... I never found out if they ticketed him or not though.

Legality aside, it's your dime in the end.. But if you play with fire, never whine if you get burned.

 

[commander315]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

I would stay little more in the wheelhouse (no pun intended) of the rating. Depending on the hull, you might even run into issues with weight, etc..

 

[hunterfab]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

Fair enough.. I go by the rule of thumb that if ya dont know its best to ask someone who does! It does have a Merc 850 85 horse on it now and I am just looking to get a little more power is all. Nothing major and I am not interested in being the fastest on the lake just as I said a little more power is all. it seems to really struggle while pulling the kids on a tube or pulling bigger folks out of the water when doing the ski thing. Top speed is only about 30 also so it just seems a little underpowered to me.

 

[clarkbre]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

Although the difference would be a 40% increase in horsepower, how much more torque does that 125 motor have? Have you tried a lower pitch prop on your 90? That may be all you need to get what you?re towing out of the water.

I?d say stay within the recommended horsepower for a two reasons:

1. Insurance. If your boat is insured, your insurance company may drop you instantly.
2. Liability. If anything bad ever happened on the water while your boat was overpowered, and it was deemed your fault, you might as well just open your wallet?the other guy could easily sue you. Oh, and your insurance wouldn?t cover you.

 

[hunterfab]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

And it does have the factory prop on it.. And NO I am not pulling the kids on the tube at 30 MPH!!! Maybe the teenagers depending on what they tore up that day! LOL just kidding..

 

[Utahboatnut]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

To me the biggest factors are 1 if you are involved in an accident you will be liable no matter what due to your exceeding the mfg rating, also if ever boarded by the CG you could be looking at a ticket. 2 the weight difference is quite a bit and may really affect how the boat handles at higher speeds.
Is the current 90 the same year as the boat? if so it seems like it should be adequate to do what you are wanting to do. Its currently running in the correct WOT range and with the correct prop? Just seems like a good running 90 on that size boat should pull a skier along easily. If you do end up doing it take the 120 stickers off the cowl at a minimum. Yes alot of people have done it, am I reccomending it NO, but its your choice.

 

[Stachi]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

I would say go with a prop change, for a better hole shot....also , being a 1993 , any chance it is water logged ??

 

[Reel Kahuna]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

I hear what all are saying..."stay within the rated capcity, weight and hp".
However what does one do when there isn't any hp rating? On my Beachcraft by Reinell cuddy hardtop that I converted the I/O to an OB but the plate doesn't list max hp. I know I'm within the rated hp being that I removed a 4.3L OMC Cobra and replaced it with a 150hp Yamaha.

 

[BLU LUNCH]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

Common sense say no , worry about your safety and your passengers safety and your fellows boaters safety.......... enough said!

 

[H20Rat]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

1. Insurance. If your boat is insured, your insurance company may drop you instantly.
2. Liability. If anything bad ever happened on the water while your boat was overpowered, and it was deemed your fault, you might as well just open your wallet?the other guy could easily sue you. Oh, and your insurance wouldn?t cover you.

Used to work in insurance, had many boats insured. Not once did our agents, or underwriting company, ever care about rated power! TOTAL power mattered, as some engine sizes as well as a magic engine/length ratio were important (which did not match the OEM size recommendations) And even then, in most cases it just meant higher rates. The only things we wouldn't touch were the muscle PWCs. 200+ HP on a single or 2 seater was a no-go for insurance.

With all that said, yes we also paid out liability claims. Not a single one denied because of engine size.


Your insurance may be different, call and find out. Personally I'd probably say go for it. That force 125 isn't exactly known as a powerful motor, and probably is more than a couple shy of 125 anyway.

As far as issues with your local DNR/sheriff, just depends if they check. Personally I've never once had a check for engine size. (my current boat doesn't even list a HP rating, only capacity) Some lakes ban 10+hp engines, you are way past being concerned about that! (I'm guessing putting some 9.9 stickers on the cowl only works to a certain point.)

 

[wca_tim]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

put it on, try it and see how it handles. if you like it, paint the cowel and put 90 decals on it...

i have a 450 horse 383 in a 17 1/2 foot checkmate that was never made with anything bigger than a 185 horse 4.3...

my insurance agent didn't care, the local law doesn't care, it has great manners, handles great, pulls the biggest slalom skier up with 1/3 throttle, gets good fuel economy and will cruise all day at 50 or 60 without even breathing hard. it also surprises the crap out of pretty much everyone that's come alongside...

too much horsepower is never enough - just like sex...

 

[hunterfab]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

Well.... I figured being the steel fabricator that I am I could either make some angle braces that go to the floor stringers or form up a bent plate to fit over the transom to beef it up.. The boat is really damn clean and I got it from the guy who bought it brand new.. Its not my first by any means and am sure it wont be my last.. the boat I owned before it was a Glastron CV-16 with a 140 horse Johnson on it.. I traded it for a plow truck because I live in the mountains and could always use another! Aint looking for a total hotrod just want some better power is all! The boat has a new floor and stringers as well as new carpet and seats and is worth putting a little money in it.. Hell even the paint and gel-coat is real nice and not a thing is missing except a little more power!

 

[CHAWK46]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

Back when I was 15 I bought my second boat, lot of years ago. It was a 15' AreoCraft with a 50 hp merc. Would'nt pull me up on one ski. So the next year I bought a used 110 merc. Pulled 2 of us up in a water start on one ski in 2 seconds. The boat didn't plane, it jumped. Every time you punched it you could hear the transom crack. Kind of stupid but I was 16. By the way, the boat was rated for 80 max.

 

[bob johnson]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

I think common sense should rule the day....if the back end is sinking its too much motor....

they made many many cars today that will do triple the national speed limit....

its all in how you drive...how about a boat so underpowered it cant get out the way, when it should...

if they can put 300 hp on the back of a 17 foot bass boat, they can put anything on a 22 footer as far as i am concerned..
I dont know about anyone else here on the site...but I have never seen a boat accident......much less one where someone got hurt..

I bet I see an auto accident a week on the road..maybe more..

if some one is hurt in a boating accident..the power of the engine is way down the list of probable causes....

outside of a state that actually has a regulation dealing with what a tag on the boat says.. i think common sense rules the day..


just one mans view

bob

 

[Frank Acampora]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

Well, take everyone's advise under consideration and then look at my 14 foot hull with a nice Force 125. She has no bad habits and goes 60 but I don't use it on crowded days.

The photos actually show it a 55 with a 90 but the 125 does go 60 and this year I will try some modifications to try for 65.

BTW: it was probably originally rated for 35-40 with a 15 inch transom

 

[4JawChuck]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

Just put a 200HP motor on my 16.5' Walleye boat, the new motor is only 70pds heavier than the old 90HP.

BTW the boat is rated for a 80HP.

If you don't know what your doing I don't recommend it, its your life.

 

[Shife]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

The capacity plate is a guideline. Local or State law may require you to follow that guideline. Federal law does not.

The issue you have is that you don't know what load the hull was engineered to handle. Unless you are the NA who drew the hull, you're guessing. It could be fine, or it could be a really dangerous and stupid idea.

If you think you have enough knowledge and practical engineering skills to roll the dice on this one, go for it. Otherwise, look into a lower pitch prop for your current motor.

Actually, you really need to find out why the boat is a dog while being powered at darn near the max hp rating. Something is fishy. You could well be trying to throw extra HP at a waterlogged and weak hull. A very dangerous situation.

 

[roscoe]

Re: Bigger engine swap.. Want to exceed manufacturers rating..Advice please.

Its a waste of time. Its a Force 125, so it will only be running on 3 cylinders most of the time anyway. So you will only be getting 90 hp in the end. hehehe