What determines the MAX HP rating for a boat?

[paulmillerplu]

Have the chance to get a 2006 225 johnson outboard.

I have a 1977 Glastron SX192 rated for 175. It currently has a 1977 Johnson 175 on it. Is there a reason I could not put the newer 225 on it? What woudl I have to do to be able to upgrade to the newer engine? Strengthen the transom or whould I have to do anything?

Is it the transom that limited the size of engine? Would that apply to a new higher horse engine that weighs the same amount?

Looking for some quicj answers as I have only two hours to decide if my boat will be able to handle the new engine or not?

Thank you for your help and input.

 

[Huron Angler]

Re: What determines the MAX HP rating for a boat?

(length x width{beam} x 2)-90=HP rating ballpark figure

For example my boat:

(16' x 5.47' x 2) -90=85.04 and my rig is rated for an 85 horse.

Hope this helps

 

[CATransplant]

Re: What determines the MAX HP rating for a boat?

There's nothing you can do to increase that rating. Going from 175 to 225 will be overpowering the boat. It may be illegal in your state, your insurance company won't like it, and it will add to your liability in case of an accident.

Don't do it. That's my advice.

 

[Silvertip]

Re: What determines the MAX HP rating for a boat?

The boat manufacturer has already done the calculation for you as the plate indicates. Boat handling is part of the reason for the HP limit. A 225 at WOT may create some serious handling issues. As pointed out, have any sort of incident regardless how serious and an attorney will have you by the short hair whether the incident was your fault or not. Your insurance company likely will balk at insuring you if they know the boat is overpowered. Not telling them it is overpowered is a guaranteed they will not cover you in the event of an accident. It is simply not worth the risk.

 

[paulmillerplu]

Re: What determines the MAX HP rating for a boat?

So it is not the weight of the outboard that determines it then?

I am doing a complete remodel of the boat when I get back from Afghanistan and there is an auction for a 2007 Mercury 225 XXL (put the wrong engine on the original post) that I could get for a song (<$1000)! Would be nice to put a new engine on her since I making her new anyway.

So it would be bad to do it then?

 

[CATransplant]

Re: What determines the MAX HP rating for a boat?

So it is not the weight of the outboard that determines it then?

I am doing a complete remodel of the boat when I get back from Afghanistan and there is an auction for a 2007 Mercury 225 XXL (put the wrong engine on the original post) that I could get for a song (<$1000)! Would be nice to put a new engine on her since I making her new anyway.

So it would be bad to do it then?

Yup. It would be bad. I thought that's what everyone already said.

 

[paulmillerplu]

Re: What determines the MAX HP rating for a boat?

Thanks for the input....I guess I will let the new engine go then...

 

[Huron Angler]

Re: What determines the MAX HP rating for a boat?

If I were you I'd get a 2-stroke Evinrude E-tec 175hp and hit the water. It only weighs 418lbs compared to a four-stroke 175 Mercury at 510lbs.

The 175 will give you plenty of speed. I ran a 60hp etec on a 17' alumnum boat and it shoots out of the hole like a banshee.

 

[mrcool]

Re: What determines the MAX HP rating for a boat?

I have a chance to buy a new cowling for my 90 hp Evinrude,(it's in like new condition) but it has 140 hp decals on it, That wouldn't be a problem would it? it's still a 90 hp even tho the cowling says 140. would the lake police be ok with that? or am I looking at a ticket or trouble from the insurance co?

 

[oops!]

Re: What determines the MAX HP rating for a boat?

hi mr cool.....

allways best to start a new thread.....but this one was over any how....

as long as the motor is rated for the boat its ok....you can put 1600 hp stickers on the side and it wont mean squat....

you wont get into any trouble from the lake cops....
on the insurance just as long as you are in the boundaries of the contract.

its when you try to put 90 hp stickers on a 175 hp motor and get into trouble that the insurance companies take offence

 

[tx1961whaler]

Re: What determines the MAX HP rating for a boat?

So it is not the weight of the outboard that determines it then?
So it would be bad to do it then?

Not the weight. The HP is what determines it. The torque produced by the prop thrust is what rips the transom off.

 

[H20Rat]

Re: What determines the MAX HP rating for a boat?

Insurance rarely will have an issue with engine size. You may pay extra for engines over a certain HP, but beyond that, they really don't care that much. (used to work for insurance, can't remember a SINGLE time we ever cared about the ratings plate.) There were certain engine/hull combinations that were deemed uninsurable, mostly high power racing PWC's and hydrostreams.

Your local law enforcement might have other issues, depending on area.

 

[Bob_VT]

Re: What determines the MAX HP rating for a boat?

It is the USCG regulations that govern the formula for boat builder's to use. It is based on the max it will safely handle.

Overpowering is not recommended........

You do realize that a 225 xxl is a very very long shaft motor

 

[Hogger]

Re: What determines the MAX HP rating for a boat?

I am in need of a new outboard , and was curious on the little HP suggestion calculator, so I punched in my numbers.
According to the calculations, my boat can take a 170hp motor, but my plate says max 90hp. That's almost double. Why the big difference?
It's a 1991 Bayliner Capri 1800.
18x7.25x2=261-90=171

 

[Bob_VT]

Re: What determines the MAX HP rating for a boat?

That formula is only one of many please do not take that answer as gospel. If you have a rating plate ....the plate is correct

 

[Hogger]

Re: What determines the MAX HP rating for a boat?

Ya, I know. Huron Anglers' was so close I was just hoping I might be able to get a bigger motor.
I'll stick with the 90.

 

[DonHof]

Re: What determines the MAX HP rating for a boat?

14.75 x 7.1 x 2 - 90 ? 119.45 So I can put a 120hp motor on a 14 foot boat?

 

[tx1961whaler]

Re: What determines the MAX HP rating for a boat?

14.75 x 7.1 x 2 - 90 ? 119.45 So I can put a 120hp motor on a 14 foot boat?

No. You really have a 14 foot boat with 7 foot beam?

 

[trendsetter240]

Re: What determines the MAX HP rating for a boat?

14.75 x 7.1 x 2 - 90 ? 119.45 So I can put a 120hp motor on a 14 foot boat?

No. Additional requirements to use the formula are that the boat have a 20" or greater transom and that it has remote steering.

When the actual plate rating takes place the boat is run at WOT throttle towards a floating pylon then turned all the way to one direction. This test is performed (among others) with increasing levels of HP until the boat can no longer maintain control during their tests.

So if your USCG plate rating says 90hp then that was the largest HP engine the boat could safely maintain control with.

 

[H20Rat]

Re: What determines the MAX HP rating for a boat?

No. You really have a 14 foot boat with 7 foot beam?

I was thinking the same thing... That has to be one ugly boat! I'd love to see a pic of it. I know there are some 15 foot mini-pontoons out, but even those don't have a 7 foot beam.

(didn't think it would be possible to get women like that on a 15 foot pontoon, with a trolling motor on the back, but i guess so!)