Maximum Outboard Horsepower Capacity (Guide and how-to)

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Country Dave
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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by Country Dave »

Check out Federal Boating Safety Act of 1971 (FBSA),

This has proven to be a hot topic for as long as I can remember and we don’t have any reason to believe that’s going to change anytime soon. It doesn’t seem to matter which side of the fence you’re on concerning this issue, what is clear is that people seem to be passionate about their opinion ”Whatever that is” and they are certainly initialed to that.

While I’m not trying to change anyone’s opinion what I am trying to do is make clear the facts and legalities of repowering any boat “above the manufacturing max HP rating” Through extensive research including numerous phone call to different governing bodies such as “local marine patrols” “Sheriff’s offices” and the “US Coast Guard” these are my findings.
Simply put “it is not illegal/against the law to repower above the manufacturing max HP rating” It’s not a criminal offence in the state of Florida.

This may be different in your state and with a little research you can easily find out. It’s certainly plausible that your state may have restrictions regarding this however; I really don’t see it as something they target or seem to be very critical about from people I’ve talked to in other states.

Let’s take a minute and look at what we do know about how a manufacture comes up with a max HP rating in the first place. There is a formula that is somewhat standard but it leaves much to the imagination and is open for interpretation. Length, with, transom thickness and height along with the hull materials all factor in. The one thing that is crystal clear is they are always going to error on the side of caution.

Safety first and being reasonable human beings we don’t disagree with that, however there is much more here to consider. What’s not so clear is, how the formula was conceived and constructed, again keeping in mind we don’t have any idea what their standards were. Was it 30% under estimated braking strength of the transom, or was it 10%? Was it 30% under a calculated do not exceed speed for the hull, or 10%? We just don’t know what the baseline criteria were for the said formula and that leaves us with more questions than answers.

From a manufactures standpoint yes safety first but believe you me they are looking out for number one and who can blame them. You can bet liability plays a huge factor when considering what they say should be the max HP motor you should but on a given hull. Any smart business will try and limit their liability as much as possible. So with that being said it’s at least reasonable to believe that there is a pretty good cushion/margin of error that favors a lower HP rating than what the hull could really handle.

In addition if you have a new boat that’s under the manufactures warranty and you over power it “ according to the max rated HP” there is a good chance the will void your warranty. How about insurance companies and your personal liability? I’ve had many boats and I’ve only insured one of them and that’s because I financed it and they wouldn’t to the deal without it. I’m just not a big fan of insurance, maybe you are but it’s a scam as far as I see it.
They will be more than happy to collect your premiums yet God forbid you have to make a claim and now you are the bad guy and it’s like pulling teeth to try and get anything done.

So before we get any further off track what do the insurance companies say about repowering above the max rated HP? Well it’s pretty diverse, no real standard form what I’ve been able to find out. It really all depends on what company you talk to. Some don’t seem to have an issue with it whiles others do and some just want a higher premium. Check it out first if you want to insure your boat and have a higher HP motor than recommended. Personally I wouldn’t tell them chit about my motor unless they asked me very specific questions and always read your policy closely. They will try anything to scam you if they can. LOL

Ok last but certainly not least what about your personal liability if you’re running a boat with a motor that has more HP than the hull is rated for? Let me say this. It’s a numbers game. Have you ever been in a boating accident? Have you ever been in a boating accident were there were injuries? Have you ever been sued over a boating accident? Yeah me ether. However some have and some will be but the chances are not likely from the data that I’ve been able to compile. The bottom line is, if you are involved in a boating accident that was a result of your negligence you may very well get sued and the layers couldn’t give a rats azz how many ponies your outboard has.
If the accident was a result of your negligent it doesn’t matter. Let me say it this way. If you get into a boat accident and it’s your fault you could be paddling it and it doesn’t change anything.

So let’s summarize.

#1 It’s illegal to put a motor on your hull that exceeds the manufactures max HP rating.” Not true in my state, maybe it is in yours. It’s not a criminal offence however you may be fined.

#2 You can’t get your boat insured or they will automatically drop you and or deny a claim based on engine HP alone. “Not true” I found that there are insurance companies that will insure you although you will pay a higher premium.

#3 You automatically assume responsibility and liability if you are involved in an accident or incident if your motor exceeds the manufactures max rated HP even if you were not negligent. “Not true” there is nothing automatic in criminal or civil law. ... 21&t=28342[/color] My Lowe 1752 Mod/rebuild
1999 Lowe 1752 Yamaha 115 HP four stroke.
1442 polar kraft 25 HP 3 cylinder Yamaha two stroke.

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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by Motv18 »

To ease some confusion don't forget to x by the modifier. .5 or .8 for hard or soft chine

230 x .5 = 115 bringing it close to the uscg tag.

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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by Y_J »

Thanks a bunch. This actually gave me a starting place. Wooot
My Fisher-Marine 1648 Build Thread ... 96#p434296

My Sears 1236 Build Thread: ... 21&t=34781

Happy Boating & Fishing,

1979 Fisher-Marine 1648
Minn Kota 35 lb thrust Bow Mount TM
Mercury 20 HP OB
1974 Ted Williams 4.5 HP OB

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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by onthewater102 »

federal regs. I can find only govern marking the max HP on the tag on the boat - it provides nothing to do with installing a motor in excess of that amount:

§ 183.53 Horsepower capacity. ...
I have a marriage license and a fishing license, but I only carry one in my wallet.

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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by thill »

You know, as I read this thread, there is one huge factor that really must be taken into consideration, particularly in an aluminum boat:


Transom construction, hull thickness, number of ribs, strakes, bunks, supports, and even the bottom contour. All of these have to factor into how much HP you put on a boat.

For instance, a 16' x 60" rowboat, made with very thin construction, 3/4" partial transom plywood, no strakes, and very few supports, may LOOK like it can easily handle a 50 HP motor, but the reality is, it will start breaking apart in short order if you start skipping across the lake in it.

Case and point, there are a lot of guys around here that will try to "soup up" their small aluminum boats by pulling the USCG plate off and adding a big motor. Sure, they will go fast, but when they go to sell it after a summer or two, you will see a dented transom, and cracks in the hull and supports. NOT the boat the innocent victim who buys it thinks it is.

Just something to think about...


1998 Crestliner 1650 Fish Hawk (Current Project Boat)
1967 Ski Barge 19' C.C, 1992 Evinrude 70 HP (Future Project Boat)
1995 Princecraft 16' - "Starfish 20", Evinrude 35 HP
1998 Sea Hunt Victory 215, Mercury 225 HP Optimax
1994 Offshore CC Bay Boat, 22' - Evinrude 150 HP

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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by onthewater102 »

I did eventually find it in the CT regs, no surprise there, if the nanny state can meddle it will...
I have a marriage license and a fishing license, but I only carry one in my wallet.

1985 Bass Tracker III

For Sale - Custom Hand Tied Jigs, Bladed Jigs,Custom Rods

2002 Alumacraft 1436LT (SOLD)

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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by earl60446 »

Yah, manufacturer rates mine for 60hp, this formula says 102 hp. It is plenty fast for me with the 48hp I got on it.
16ft 1989 Fisher SV-2 w 1988 48hp SPL Johnson "CIGAR BARGE"
(engine looks like a wreck but runs great)
Used to have 1972 14ft Lund w 1977 15hp Mariner
(engine looked great but always ran marginal)

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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by rednecknproud21 »

This helps alot. Plenty of good information on this site.

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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by DaleH »

... fairly close when checking my boats specs...
Way off ... as in 40% HIGH :shock: ... when assessing my 16' Starcraft specs.

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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by ppine »

Or look at the plate riveted to the hull with hp rating.

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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by RiverRoost »

Thanks. Good information.
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Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by gnappi »

Using my 2017 Lowe 1040 the calculations come out as shown if I measure the transom width as in the graphic below. The calculations either come out conservative or over but, failing not having factory specs this may help some with older boats or those where specs are not available.

Note: The 48" measurement was taken inside the boat.
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Gary (in South Florida)