Outboard rating question

jbouwman25

Recruit
Joined
Jun 8, 2008
Messages
2
My brother has a 17' aluminum deep-v that is rated for 150 hp. He needs a different outboard and is thinking of buying a new Evinrude E-tec 150hp. But he also has the possibility of buying a used '06 or '07 (can't remember) Evinrude E-tec 200hp from a relative. He would like to go with the 200hp as it would be cheaper but he doesn't know if he should exceed the outboard rating. Keep in mind that the 200hp and the 150hp are built on the same block so the dry weight is the same. Is it still not a good idea to go with the 200 hp? He's not concerned with insurance, whether it's legal or not, etc. He'll find that out later. He just wants to know if the power of a 200 hp will be too much stress on the hull?
 

5150abf

Vice Admiral
Joined
Aug 12, 2007
Messages
5,808
Re: Outboard rating question

The weight of the motor isn't what causes the problem it is the thrust.

The people that built the boat say that hull can reliably handle 150 horse.

The problem is by the time you figure out the motor really was too big is right after it gets really quite exept for the blurp blurp of the motor sinking after it rips the transom out.
 

tashasdaddy

Honorary Moderator Emeritus
Joined
Nov 11, 2005
Messages
51,019
Re: Outboard rating question

The United States Coast Guard has an opinion on this frequently asked question, and their answer from their website is reproduced below:
Can I use a bigger motor on my boat than what it's rated for?
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.
There are no Coast Guard regulations against exceeding the safe loading capacity, however, there may be State regulations or restrictions from your insurance company which prohibit this. There is a Coast Guard regulation that gives Coast Guard Boarding Officers the power to terminate the use of a boat (send it back to shore) if, in the judgment of the Boarding Officer, the boat is overloaded. There is no fine for this, unless the operator refuses the Boarding Officer's order. We certainly hope that you will abide by the rating, as overloading may lead to capsizing or swamping of the boat.
NOTE: The Coast Guard Capacity Information label is required only on monohull boats less than 20' in length. The label is not required on multi-hull boats, pontoon boats (catamarans), or on any sailboats, canoes, kayaks, or inflatable boats, regardless of length.
As the Coast Guard mentions, local regulations may apply. For example, in the state of Ohio one should be guided by this regulation:
Capacity Plates
(ORC 1547.39 & ORC 1547-40)
No person shall operate or permit operation of a watercraft in excess of any of the stated limits on the capacity plate. When no capacity plate exists, no person shall operate or permit operation of a watercraft if a reasonably prudent person would believe the total load aboard or the total horsepower of any motor or engine presents a risk of physical harm to persons or property.
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: Outboard rating question

Some folks will tell you that it doesn't have to be run at WOT. I agree, but I know boaters. . .it WILL be run at WOT and it will probably break the boat.

Urge him to stick within the maker's recommendations.
 

haskindm

Petty Officer 1st Class
Joined
Jun 12, 2008
Messages
255
Re: Outboard rating question

The people that engineered and built your boat say that the maximum power for it should be 150 horsepower. If you are not going to believe them, why would you pay any attention to what a bunch of people on a boating forum say?:confused:
 

SnappingTurtle

Lieutenant
Joined
May 4, 2008
Messages
1,251
Re: Outboard rating question

The people that engineered and built your boat say that the maximum power for it should be 150 horsepower. If you are not going to believe them, why would you pay any attention to what a bunch of people on a boating forum say?:confused:

Nice point. :)
 

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
16,313
Re: Outboard rating question

The people that engineered and built your boat say that the maximum power for it should be 150 horsepower. If you are not going to believe them, why would you pay any attention to what a bunch of people on a boating forum say?:confused:
I might agree with your statement if the maximum HP was decided using sound engineering principals. Unfortunately the maximum horsepower is determined using a dimensional formula that does not take into consideration the design or the materials used in the construction of the hull. A boat made of ?? plate steel and one made of 1/8? balsa wood have the same HP rating.

Does this make sense to you?


In response to a mandate from Congress contained in the Federal Safe Boating Act of 1972 (FSBA), the United States Coast Guard issued regulations covering small outboard boats and the maximum rated horsepower for them. The regulations bind the manufacturer to provide a capacity plate that shows the maximum rated horsepower for each hull.

The applicable regulations can be found in 33CFR183.53 The manufacturer must state the horsepower as no more than that computed under the formula, except, if the manufacturer conducts the performance testing procedure, the results of that testing can be used (with some qualifiers). However, the manufacturer is apparently free to state a lower rating if desired, and sometimes does.

The formula provided in the regulations reduces to:

(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.
 

Bob_VT

Moderator & Unofficial iBoats Historian
Staff member
Joined
May 19, 2001
Messages
26,064
Re: Outboard rating question

If the engine is such a good deal.... find out it's trade in value to buy it and trade for an e-tec or consider changing boats.
 

dajohnson53

Lieutenant Commander
Joined
Apr 28, 2004
Messages
1,627
Re: Outboard rating question

I might agree with your statement if the maximum HP was decided using sound engineering principals. Unfortunately the maximum horsepower is determined using a dimensional formula that does not take into consideration the design or the materials used in the construction of the hull. A boat made of ?? plate steel and one made of 1/8? balsa wood have the same HP rating.

Does this make sense to you?

I don't think that's necessarily true. It is true that many (most?) manufacturers go strictly by the formula. I know mine did - but my boat is made by a local, low volume boat builder and I don't think he has any other basis. Frankly, I'm not sure that the hull is actually strong enough for the rated HP, but that's a different story.

On the other hand, I don't believe manufacturers are required to use that formula: they can deviate higher or lower depending on how they design their hulls. I have heard that some manufacturers have a HP rating that is not necessarily consistent with the formula you included. Hopefully someone can chime in with examples.

In looking at the formula you listed - I thought that there were also factors in the formula for height at the transom and whether the hull was designed for tiller or remote steering? It's been a long time since I actually looked at the USCG site where the formula is listed, so maybe my memory is faulty... although plugging in the numbers for my boat (approximately 21 feet long, 7 foot beam at transom), it comes about right to my rated HP: 200.
 

JoeCrow

Petty Officer 1st Class
Joined
Nov 1, 2007
Messages
218
Re: Outboard rating question

(2 X L X W) -90 = rated horsepower

using the above formula, my 19' Bayliner should be rated for at least 175hp
2x19=38x7=277-90=176
My boat is only rated at 125
So someone either doing added engineering or they're doing a great job of covering their *****e$ from law suites
I'd stay with the plate recommendations
God forbid if you were ever involved in an accident or worse a fatality
They would hang you in a Civil Court
 

Kev144

Petty Officer 2nd Class
Joined
Oct 16, 2007
Messages
159
Re: Outboard rating question

(2 X L X W) -90 = rated horsepower

using the above formula, my 19' Bayliner should be rated for at least 175hp
2x19=38x7=277-90=176
My boat is only rated at 125
So someone either doing added engineering or they're doing a great job of covering their *****e$ from law suites
I'd stay with the plate recommendations
God forbid if you were ever involved in an accident or worse a fatality
They would hang you in a Civil Court

That formula cant be correct. According to it, my Charger woiuld be rated for a 90hp when it has a 150 on it (rated for) and soon to be 2.5L merc.
 

mthieme

Captain
Joined
Oct 6, 2007
Messages
3,270
Re: Outboard rating question

The quote from the USCG above is interesting considering they used to run 115 Johnnies on the back of 17' whalers....about 30 +/- over the rating!
 
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