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Author Topic:   Over-powered boats
Dr T posted 09-03-2001 02:11 AM ET (US)   Profile for Dr T   Send Email to Dr T  
In reviewing the thread on Boat Speed (, it strikes me that there are quite a few of the minor Cetaceans running around with more than their rated horsepower.

The notion of hanging a 50 on the back of my 13 is interesting, since I am running up here in the Rockies (where my '82 Johnson 35 may actually be putting out more like 15 HP). It would be nice to have more power, and it may be easier to find a 50 than a 40.

As I understand it, the rated horsepower is based largely on the strength of the transom.

What are the expected long term effects on the hull that will result from running a motor more powerful than the rated horsepower (besides more bugs in the teeth)? If one decides to go this route, what other factors will come into play?

Tom W Clark posted 09-03-2001 06:04 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Dr T,

The horsepower rating of a given boat has nothing whatsoever to do with the strength of the transom. It has little to do with demonstrated performance either, rather, its origin is formulaic.

The strength of a given boat's transom may have a lot to do with the wisdom of a boat owner's decision to overpower. If the transom on your 13 is suspect, then perhaps it is wise to avoid overpowering. Unless you have reason to suspect your boat has a problem then I wouldn't worry about it. The 13' Whaler is one of the most commonly overpowered boats in the world. Most of those have 50 hp motors on them. Being at high altitude means, as you have observed, that you will not be achieving the rated horsepower anyway.

Whether an overpowered, or rated-powered, boat withstands the stress of the motor mounted to its transom has much more to do with how it is driven than anything else. A 50 hp motor only generates 50 hp at WOT. If one has an overpowered boat but rarely uses full throttle, then the boat doesn't know the difference.

I can assure you that a teenager running around in a 13' Whaler with a 35 hp motor, jumping boat wakes, water skiing, and generally horsing around all day long will put far more stress on the boat's transom than a boat with a 50 hp driven by a sensible adult who is averse to getting his butt pounded on a choppy day.

SuburbanBoy posted 09-03-2001 02:22 PM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     
All I can say is, I wish my 15' was over-powered. I miss the punch of an overpowered boat. That said, I would not trade my security, safety or confidence inspiring stability for any of my older, non-Whalers.


Dr T posted 09-03-2001 11:45 PM ET (US)     Profile for Dr T  Send Email to Dr T     
This inspires a follow up question.

I noticed that on that the maximum motor weight is 210 lbs for the 13. Does this mean that a engine like the 4-stoke Yamaha 50 hp (at about 235 lbs)cannot be used? If I get an engine that heavy, how much am I going to tempt fate?



Flipper posted 09-04-2001 01:05 AM ET (US)     Profile for Flipper  Send Email to Flipper     
I was worried at first about putting
a 90 on my 15, but my decision on going
ahead was based on : 1) I was going to be
the only driver and 2) I am at the age where I can put wake jumping, etc. behind me, so
stress on the transom was a non-issue.

I agree with Tom about conducting yourself accordingly.

Bigshot posted 09-04-2001 04:20 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Buddy saw a 17' Montauk yesterday with a 200hp evinrude. It was named Attitude Adjuster. He said she sat way low.
Flipper posted 09-04-2001 09:37 PM ET (US)     Profile for Flipper  Send Email to Flipper     
That's terminal!Is Chuck Yeager still alive?

Eric posted 09-06-2001 10:58 PM ET (US)     Profile for Eric  Send Email to Eric     
Bigshot: a 200 on a Montauk? Was that here in Bradenton? I'd like to see it, but not from too close!
Bigshot posted 09-07-2001 10:30 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Beer can beach at long boat pass. That is what I hear. When you coming out there?
Buckda posted 09-07-2001 06:39 PM ET (US)     Profile for Buckda  Send Email to Buckda     
Dr. T
The other aspect you should think about is the fine you might incur if you overpower your boat. I believe it is a $150 fine in Michigan for the first offense, and rises sharply from there. That said, I have seen plenty of boats (Whaler and non-Whaler) that have more than the recommended horsepower hanging off the transom, which leads me to believe that if you're driving your craft in a sensible manner, most coasties and law enforcement will take a more lassaiz-faire attitude. I suspect that if you're caught for misbehaving, though, they'll probably tack the overpowering fine on to your tab.

That's MHO.

Tom W Clark posted 09-07-2001 11:09 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Dr T is in Colorado, so it's federal and Colorado state law that he needs to be concerned with.

I have never heard of it being illegal to have and run an overpowered boat. I know there are no laws against it in Washington State nor are there any federal laws against it, so the Coasties won't be able to fine you for being overpowered. If Michigan has such a law it is the first one I've ever heard of.

Having said all that, if you choose to run your 13 footer at 60 m.p.h. and kill someone in the process then it may not work to your favor that you exceeded the maximum horsepower rating of your boat.

Dick posted 09-07-2001 11:24 PM ET (US)     Profile for Dick  Send Email to Dick     
Another thing to take a look at is your insurance policy. Most insurance companies take a dim view of an overpowered boat. Keep in mind that if something should happen and you have no insurance because of overpowering, $$$$$$$$$ out of your pocket.
sorcerer posted 09-08-2001 06:26 AM ET (US)     Profile for sorcerer    
Do a search on "outboard motor regulations" by state, I used Goggle. A lot of states have laws directly prohibiting the use of motors rated higher than the boat manufacture's rating, some with fines.

In the case of Washington State the this is somewhat an arbitrary decision based on conditions, and circumstances. Reference 79A.60.180

Tom Clark is correct as far as the USCG, however if it is a state law they can enforce it.

sorcerer posted 09-08-2001 06:30 AM ET (US)     Profile for sorcerer    
I am sorry the "url" above will not work. For your reference please look up the regulation here: using the number listed above.
Dr T posted 09-09-2001 01:23 AM ET (US)     Profile for Dr T  Send Email to Dr T     
Thanks for the feedback.

The situation in Colorado on maximum power is a bit obscure. It says that the Maximum power is to be permanently displayed. I cannot find in my review of the Colorado boating regs where the maximum power is not to be exceeded.

There are also regs about operating in a manner suitable to the conditions.

The real issue is not pushing the maximum power beyond 40, but how to operate efficiently at a wide range of altitudes. A 50 HP motor is one approach to this (more horsepower would give a greater margin for error). For the time being, I will probably be content to play around with the old 82 Johnson 35 HP (change the jets, etc.) Eventually, however, the engine will probably blow.

What I really need is a light (~200 lbs), EFI 4 stroke 40 hp engine that will produce close to its rated horsepower at 9000 feet.

Any suggestions?

Dr T posted 09-11-2001 11:03 AM ET (US)     Profile for Dr T  Send Email to Dr T     
A discussion of the philosophy of this issue is found at

The post from Peter gives a link to the formula.

The basic formula for maximum power for a boat with a steering console is

(Length in feet x transom width in feet x 2) - 90

with rounding down on the calculation to the nearest 5 (and I suspect rounding down on the mearsurements as well).

Without the rounding (and using my handy tape measure), the sport 13 comes up with

(13.5x5x2)-90 = 45.

If the transom was 3 inches wider (which the boat is at the beam), then the calulation would be 52.


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